Abstract: A device for detecting dental caries has an illumination device which emits radiation of a pre-determined wavelength towards a tooth. A filter accepts radiation returned by the tooth in a pre-determined spectral range. The accepted radiation is evaluated for caries detection. The illumination device has at least one light guide, by means of which the radiation can be supplied to the tooth. The illumination device emits radiation in the spectral range from 360 to 580 nm. The filter accepts the returned radiation in the spectral range above 620 nm. The device can be used in a flexible manner and enables a low level of caries to be identified.

Abstract: A fire alarm system which radiates light towards a smoke detecting space. Scattered light resulting from smoke that may exist in the smoke detecting space is judged by a receiver with respect to the type of smoke that may prevail in the space. The presence of a fire is judged by comparing the light that has been received with a set threshold level. The threshold level is set to different levels in accordance with the type of smoke detected.

Abstract: Disclosed is a method and apparatus for measuring particles in a fluid by irradiating the fluid containing the particle with a laser beam and deriving particle characteristics such as diameter and size distribution from the intensity of the light scattered by the particles. Based on the value of the output of a photomultiplier used to detect the scattered light, it is determined whether a particle is a fine particle, which is a particle with a photoelectron pulse count that does not exceed a prescribed value, or a large particle, and these particles are counted separately. Fine particles are processed using photon counting, and large particles are processed by an analog process, in which case the threshold values used to discriminate particles are varied in accordance with pre-stored data on the refractive index of each fluid.

Abstract: A mixture is prepared by mixing carriers to which a substance specifically reacting on an object substance adheres with a sample containing the object substance. The mixture is irradiated by light having an intensity gradient to concentrate the carriers at and near the irradiated positions by the optical pressure of the light. The efficiency of an agglomeration reaction of the carriers is thereby increased. A qualitative or quantitative measurement of the object substance is performed by detecting a state of agglomeration of the carriers within the mixture.

Abstract: A method for detecting the presence or absence of microorganisms in a liquid test sample is provided without need for withdrawing an aliquot or destroying the sample. The method comprises taking near-infrared spectra of the sample and comparing it visually or mathematically to the spectra of a standard, which may be the values of the spectra known to the operator or may be a standard sample that is provided and run side-by-side.

Abstract: An apparatus and method are provided for the noninvasive and nondestructive detection of microorganisms within a liquid product contained within a sealed vial. The apparatus includes a near-IR light source that produces both incident and reference beams having a wavelength between 800 and 2500 nm and, more preferably, 1100 and 1360 nm. The apparatus also includes an integrating sphere having incident and reference beam ports and a sample window opposite the incident beam port. A detector is mounted in the integrating sphere substantially adjacent the sample window. A substantially U-shaped mirror is provided to hold the vial. The U-shaped mirror is of a size substantially corresponding to the diameter of the vial. In operation, the incident beam is directed through a sample window so as to enter the vial adjacent a sidewall of the mirror. In this way the U-shaped mirror reflects the incident beam so that it passes through the vial three times before returning to the detector.

Abstract: Methods and apparatus using the principles of time-resolved spectroscopy are disclosed. The present invention employs incident light pulses of sufficiently short duration to permit the rate of the rise and decay of such pulses to be measured. Consequently, the rate of decay, u, permits a determination of the concentration of an absorptive pigment, such as hemoglobin. The present invention also allows the precise path length the photons travel to be determined. Using this path length information and by measuring changes in optical density using known continuous light (CW) spectrophotometry systems, the methods and apparatus disclosed allow changes in the concentration of an absorptive pigment to be correctly be measured. From these data, the oxygenation state of a tissue region, such as the brain, can be accurately determined in real time.

Abstract: A device of measuring a blood coagulating time, the device being constructed such that when the specimen is placed in a detecting section in which it is maintained at a desired temperature, the measuring initiation time is set, followed by the transmission of a series of measuring data to a memory through an arithmetic circuit until a saturation is reached in response to which the measuring operation is stopped. On presumption that the saturating value is 100%, arithmetic operation is conducted, the results of which are stored in the remaining space of the memory. The device includes a keyboard switch whereby a time corresponding to particular percentages, such as 20%, 50%, and 80%, is previously set so as to enable the time to be easily recognized and accurately reproduced.

Abstract: An oximeter that measures both the total hemoglobin concentration in whole, undiluted blood and the percentage of the hemoglobin saturated with oxygen. The oximeter uses red and infrared light-emitting diodes to illuminate a capillary tube filled with a sample of whole, undiluted blood. Light scattered by the blood travels a short distance down the length of the capillary tube and reaches a photodetector, the output of which is amplified, digitized, and fed to a microprocessor. The microprocessor computes the total hemoglobin concentration as a nonlinear monotonic function of the infrared light intensity. Oxyhemoglobin saturation is computed from the ratio of the logarithms of the intensities of red and infrared light. The invention provides a measurement of oxygen saturation without calibration shifts present in other oximeters due to fluctuations in total hemoglobin concentration.

Abstract: Laser-warning method and a laser-warning arrangement, which laser-warning arrangement is intended to warn of laser light from a laser beam source which is used for guiding projectiles, missiles and the like, for example laser light from a pulsed laser beam which is directed towards a target area. The time for the laser beam to reach the laser-warning arrangement, the so-called impact time, is calculated from a first amplitude value, measured at a first point in time, of the scattered light from the laser beam and a second amplitude value, measured at a second point in time, of the scattered light from the laser beam, and the measured time difference between the said first and second points in time on the basis that the amplitude raised to a constant is proportional to the distance to the laser beam according to the equation D=K.multidot.A.sup.n, where K and n are constants, D is the perpendicular distance to the laser beam and A is a measured amplitude value.

Abstract: A method of immunoassay for analyzing a bodily fluid for the presence of an analyte relies on observing substantially the entire course of a precipitin reaction from initiation to substantial completion of the precipitation, defining a mathematical function which represents the amount of precipitation versus time and contains constants which can be adjusted so that the function matches the observed precipitation versus time curve, and fitting the observed data to the mathematical function by adjusting the constants so that the mathematical function matches the observed precipitation versus time curve as closely as possible. Values for the maximum rate of precipitation and for the time interval from initiation of the precipitation to the time of maximum rate of precipitation are calculated from the mathematical function. A reference curve is generated using standard containing known concentrations of analyte according to conventional analytical procedures.

Abstract: The method of the present invention employs an enzyme immunoassay for measuring the concentration of an analyte in a sample by indirect colorimetric detection. An incident light beam at a plurality of wavelengths is directed into a liquid solution containing an analyte of interest. The solution is capable of attenuating the amount of light at a first wavelength received from this solution as a function of the increasing concentration of the analyte present. A light signal from the solution at the first wavelength is detected, and light at a second wavelength, at which substantially no attenuation of light signal occurs as the concentration of the analyte increases, is also detected. The ratio of the two respective wavelengths is formed and that ratio is compared with ratios of known amounts of the analyte to determine the amount of the analyte in the sample.

Abstract: The invention relates to a device for detecting the presence of extraneous substances in a medium in the vicinity of a wall separating two mediums.The device provides in the medium I illumination of a wall under a radiation corresponding to the transparency of the semi-transparency of the material of the wall on a reference illumination zone. Directional detectors permit covering of the reference illumination zone, the mean direction of the reception cone having with respect to the mean direction of the beam an inclination such that the intersection volume of the beam and of the reception cone is a minimum.Application to the aid of driving of automobiles or airplanes and the control of industrial chemical processes is disclosed.

Abstract: In an optical instrument for measuring particles in the size range of 0.5 microns to 300 microns, a laser beam is caused to pass through a sample stream of liquid containing particles to be measured. A photodetector detects a portion of the direct laser beam passing through the sample stream and the amplitudes of the pulses generated by this first photodetector provide a measurement of particles in the size range of 10 to 50 microns. A second photodetector detects forward scattered light from the laser beam passing through the liquid sample stream. The amplitudes of pulses generated by the second photodetector provide a measurement of pulses in the size range of 0.5 microns to 10 microns and the durations of pulses generated by the second photodetector provide a measurement of pulses in the size range of 50 to 300 microns.

Abstract: The peak verify time for kinetic nephelometric measurements of reactions between antigens and antibodies is adjusted as a function of the magnitude of the peak rate order to reduce the time required for peak verification. The scatter signal is zeroed following the end of the peak verification period and the reaction is tested for antigen excess. Reactions during the antigen excess check having rates that exceed a threshold value are accepted as being valid, and no additional measurements are made for such samples. Reactions during the antigen excess check having rates that are less than the threshold value are rejected as being in antigen excess. Samples found to be in antigen excess are diluted and then reanalyzed.

Abstract: A coherent laser light flux is projected into a cell made of transparent quartz and light scattered from particles suspended in an antigen-antibody reaction liquid contained in the cell is detected by a photomultiplier by means of a collimator. An output electrical signal from the photomultiplier is sampled at different time instances and samplings are supplied to a fast Fourier transformer to derive a plurality of power spectrum desnities of fluctuation in intensity of the scattered light. A plurality of power spectrum densities are averaged to generate a mean power spectrum density. An amount of antigen contained in the reaction liquid is measured in accordance with the mean power spectrum density.

Abstract: A system for detecting contaminant particles in a liquid, such as used for processing wafers during the manufacture of integrated circuits, distinguishes non-contaminant bubbles generally found in liquids from contaminant particles. The system provides a controlled laminar fluid flow of the liquid through a pipe, and the substantially spherical bubbles in the flow path are detected by symmetrically spaced photodiodes. The irregularly shaped contaminant particles are detected, whereas the presence of bubbles are negated by the detection system by virtue of the balanced photodiode assembly.

Abstract: A coherent laser light flux is projected into a cell made of transparent quartz and light scattered from particles suspended in an antigen-antibody reaction liquid contained in the cell is detected by a photomultiplier by means of a collimator. An output electrical signal from the photomultiplier is sampled at different time instances and samplings are supplied to a fast Fourier transformer to derive a plurality of power spectrum densities of fluctuation in intensity of the scattered light. A plurality of power spectrum densities are averaged to generate a mean power spectrum density. An amount of antigen contained in the reaction liquid is measured in accordance with the mean power spectrum density.

Abstract: A biological microparticle inspection apparatus has a reactor in which blood containing T cells is mixed with latex-labeled antibodies and T cells are coupled with the antibodies to form complexes. A particle size measurement unit is provided for measuring the size of the particles contained in the blood, including the complexes. A signal processing unit processes the measured sizes of the particles outputting signals only when the measured sizes fall within a range of the size of the complex, and counts the number of the output signals. The number of the output signals corresponds to the number of the complexes and hence the T cells.

Abstract: In order to eliminate equipment-generated fluctuations during the periodic determination of a quantity to be measured which is effected by forming the difference between a measuring signal which has been altered relative to a source signal by the measurement variable and a reference signal which has remained unaffected relative to the source signal by the measurement variable, a base signal level is determined for each measuring cycle as the difference between the reference level and a zero level in the absence of a source signal, subsequent to which each actual reference signal level and each measuring signal level is compensated with the previously determined reference signal level. By amplifying the compensated reference signals prior to difference formation and standardizing the signal difference to the base signal level, a high degree of accuracy may be achieved even if the attenuations of the measuring signal caused by the quantity to be measured are very small.

Abstract: A method of renewing a used liquid for reuse of the same includes establishing a body of a reference liquid for comparison with renewed used liquid, and establishing a separate body of the used liquid adjacent the body of reference liquid. An incident light beam is produced for consecutive traversal of the body of used liquid and the body of reference liquid, the particles in the two liquid bodies thereby diffusing the light beam to provide respective luminous fluxes off the axis of the incident light beam. The two luminous light fluxes are separately detected and compared. This procedure is automatically terminated when the detected luminous light fluxes are substantially equal to each other.

Abstract: An automatic analyzing apparatus for effecting chemical analyses for various sample liquids such as blood, urine, and the like, comprising a sample delivery pump for metering a sample liquid into a reaction cuvette, a reagent delivery pump for delivering to the reaction cuvette a given amount of a given reagent selected from a plurality of reagents contained in a reagent cassette, to form a test liquid, a feed mechanism for successively supplying reaction cuvettes along a circular reaction line, a plurality of photometering sections arranged along the reaction line for effecting a plurality of photometric and/or nephelometric and/or fluorometric measurements for each test liquid at different time instances to produce a plurality of photometric results, and circuitry for receiving the photometric results and selecting therefrom given quantitative analytical data of a given test item.

Abstract: Method for the measurement of the difference in the optical properties dependent on the light direction of two samples (1,2), in which method one or several sources of light (3 to 6) as well as one light detector (7) are used. According to the invention, both of the samples (1, 2) are illuminated simultaneously and from both samples (1, 2) the light is passed simultaneously to the light detector (7). The lights to be measured from the samples (1, 2) have different directions in relation to the sample. The directions of the lights to be measured from the samples (1, 2) are alternated with each other at an appropriate frequency, such as a frequency within the range of 1 c/s to 10,000 c/s. The AC signal given by the light detector (7) is used as a measure of the difference in some optical property dependent on the direction of light between the samples, such as, e.g.

Abstract: The disclosed methods improve conventional agglutination processes for assaying immunoreactive and like substances, primarily by improving the measurement of the agglutination itself. Suspensions containing agglutinated particles are automatically inspected, preferably intermittently during the agglutinating reaction, and the resulting data are processed to identify individual particle aggregates of a selected limited class, which may, for example, comprise aggregates having sizes within a limited size interval. The numbers of such aggregates are compared with corresponding reference values obtained with standard solutions and suitable controls to evaluate the concentration of one of the reactive substances, or other information. The aggregate size intervals and other parameters which are used to define aggregate classes are preferably selected with attention to the detailed behavior of each test system.

Abstract: A steam wetness measuring apparatus comprises a light source, a part defining a measuring space when the apparatus is inserted into a wet steam flow, an optical fiber bundle for transmitting the incident light beam from the light source to the measuring space, and optical fiber bundles for transmitting to a photo-electric converter element a plurality of scattered light beams of different scattering angles obtained by radiation of the incident light beam on the measuring space. The fact that the intensity of the scattered light beam changes with the wavelength of the incident light or changes with the scattering angle of the scattered light beam, in accordance with the particle size distribution of water droplets in the wet steam is used to determine the particles size distribution. The steam wetness is determined from the particles size distribution and the physical properties of the wet steam flow.

Abstract: A method and apparatus for detecting the presence of caries in human teeth using visible light. The tooth is exposed to light of relatively narrow bandwidths. The light from the tooth is preferably examined by two photomultipliers or visually each examining a different wavelength. Caries are detected when the difference in the intensity of the light from the tooth at those two wavelengths changes in a predetermined manner.

Abstract: A technique for measuring the degree of an antigen-antibody reaction by preparing a suspension of insoluble microscopic carrier particles of at least one type carrying an antigen, an antibody or a hapten, forming an agglutination promoting or inhibiting reaction system among the insoluble carrier particles based on an antigen-antibody reaction using the suspension and one or more antigen, antibody or hapten, irradiating the solution of the reaction system with laser light and detecting the light scattered from the reaction system at one or more specific angles, detecting a signal indicative of one or more specific frequency bands from the resulting scatter spectrum, and thenceforth calculating the quantity of antigen, antibody or hapten in a specimen on the basis of the detected signal. The intensity spectrum output of filter 11 for frequency band selection is in the form of a square root and is converted into the original intensity spectrum by means of a squaring circuit 12.

Abstract: Two embodiments of the visibility meter are disclosed. In the first embodiment, light transmitted from the light transmitter and light received by the light receiver is propagated in a conical beam. The beams are so oriented that they include an obtuse angle. In the first embodiment, a partition blocks all direct transmission of light from the light transmitter to the light receiver. In the second embodiment, direct transmission of light from the light transmitter to the light receiver takes place through the partition, but is limited to a predetermined level.

Abstract: A liquid flow photometer for fluorescence light and/or scattered light measurement, having a measuring area (37) where particles (38) flow through. The device comprises a first objective (3) focussing excitation light (5) in the measuring area (37) and also collecting fluorescence light emanating from the measuring area (37). The first objective (3) is modified by a slightly transparent central stop (39) placed in the rear focal plane of the objective. The device further comprises a second objective (23) collecting the light falling within the conic sector (40) obscured by the central stop (39). This light contains partly scattered light and excitation light. The corresponding photo-electric signal is divided in a pulsed (AC) component and a constant or slowly varying (DC) component. The DC component serves to correct one or both of the AC components representing the fluorescence and scattered light intensity in order to make them independent of variations in the excitation light intensity.

Abstract: A laser light beam is projected through a fluid measuring cell having a fluid accommodating chamber and inlet and outlet pathways for the fluid. The light is separated into transmitted light and scattered light. Separate light detectors sense the transmitted light and scattered light. An electric control circuit uses the variations of the intensity of the transmitted light to compensate for fluctuations in the intensity of the scattered light to provide an output related to the intensity of the scattered light.

Abstract: A method for measuring substantially spherical particles, such as dust. Two signals are formed, one of which is an approximately linear function of the particle concentration independently of the particle diameter and the second one is an approximately linear function of the particle diameter independently of the particle concentration. In order to obtain these signals the particles are illuminated with light in a direction different from their direction of flow. At least two detectors are arranged in such a way that the light in the beam path from the light source (3) to the first detector (6) is substantially only influenced by scattering and by light absorption of the particles and that the light in the beam path from the light source to the second detector (7) passes substantially only via reflections against the particles. The two signals are formed by definite relations between the d.c. voltage components of the output signals of the detectors and the average value of the squared R.M.S. value of the a.

Abstract: A nephelometric immunoassay and a nephelometer therefore, characterized in that light is projected on a sample to-be-measured containing an antigen-antibody complex, that at least two light scattering intensities at different angles with respect to the incident light are measured, and that a true antigen concentration is discriminated by comparing the light scattering intensities.

Abstract: An automated pipette employing a device to ensure exact volume pickup and delivery. An optical device senses the presence of a liquid in the tip of the pipette. By intaking the volume past the optical device stream continuity is determined.

Abstract: A nephelometer and method for measuring optical quality of a marine atmosphere and particularly characterizing its aerosol particle size distribution, visual range and aerosol optical effects in the visible and infrared. There is provided a housing for entrapping a momentary aerosol sampling, a laser source for providing a narrow collimated beam of radiant energy (usually light) through the sample, and plural spaced-apart cosine sensors facing across the radiant energy illuminated sample, with one reading a slightly greater angle than the other, for receiving aerosol particle scattered light. Integrated outputs from the sensors when compared with laser output intensity as a reference signal provide an indication of aerosol particle size distribution and concentration.

Abstract: Light operative apparatus is located inside electro-optical instrument viewing window, such as that used by a radiation pyrometer or dimensional gage in a steel mill environment, to detect and compensate for optically attenuating objects which may accumulate on the outside surface of the viewing window. Light beam irradiates viewing window from inside and optics collects light radiation backscatter which varies as a function of light-scattering attenuating objects that have accumulated on the viewing window outside surface. A light backscatter detector feeds display, alarm and instrument compensation functions.

Abstract: The concentration of a selected gas specie at a situs determined by directing a laser beam at the situs, the beam including a wavelength within the resonance absorption band of the gas specie, and measuring the intensity of the laser beam energy scattered from two spaced volumes along said beam at the situs. The ratio of measured intensities is a relative measure of the concentration of the gas specie at the situs.

Abstract: In the smoke opacity monitor disclosed herein, a measurement of opacity is obtained by measuring the proportion of polarized light from the background sky which is detectable through the smoke plume. Compensation and normalization is provided to minimize errors generated by illumination of the plume itself and for the overall intensity of the background sky light.

Abstract: A device for measuring the visibility, or diffusion coefficient, of atmosre air, including a light source for directing light onto a volume of air and a receiver capable of measuring the flow of light diffused by the volume of air. The source is surrounded by ambient air and furnishes a beam diverging in essentially all directions except within at least one dark cone. A receiver opening is directed toward the source, but is located in the dark cone so as to receive only diffused light. The apparatus is for use in meteorological installations, notably in airports.

Abstract: Precise quantification of turbidity is obtainable through multiple determinations of the light attenuation coefficient of the particulate-bearing medium at a plurality of path lengths in the attenuating medium, and through multiple determinations of the scattering coefficient of the particulate-bearing medium at a selected angle of incidence and at a plurality of path lengths in the attenuating medium. In the preferred apparatus, these determinations employ a common light source and a common detector. In the present system, there are eliminated such adverse factors as light-source instability, detector instability, variations in particulate deposits on windows, and other problems, through the use of the ratio of the intensity measurements at different locations in the medium.

Abstract: The invention relates to the measurement of the shade of a particle. The particle is illuminated with light of variable intensity and viewed against a background level of illumination. A measurement is made of the ratio of time for which the intensity of light from the particle exceeds the intensity of the background to obtain a measurement of the shade of the particle.

Abstract: A method of determining the concentration of antigen in a rate nephelometric immunochemical analysis wherein an observed maximum rate of change of a nephelometric signal is used to determine the antigen concentration by employing a mathematical expression derived on a semi-empirical basis.

Abstract: End point detection in developing photoresist is accomplished by monitoring the output of a photodetector and sensing a plateau in the output.

Abstract: According to the invention, the instrument for measuring the sizes and quantity of particles in a fluid medium comprises a light-sensitive device which converts light scattered by particles in a flow of a fluid medium which crosses a beam emitted by a light source, as well as some part of the light of that beam, arriving from an element whose purpose is to simulate a calibrated particle, to electric pulses. The light-sensitive device is connected via a divider, whose purpose is to distribute pulses according to the sizes of particles, to signal inputs of respective threshold devices whose outputs are connected to inputs of counters with indicators. The element which simulates a calibrated particle is adapted to periodically change, in the course of measurement, the brightness of light received by the light-sensitive device.

Abstract: A method of determining the need for post-addition of antigen or antibody to an antigen-antibody reaction to ascertain whether the reaction is in an antigen excess or an antibody excess condition. The time rate of change of a nephelometric signal developed from the reaction is monitored to generate a rate signal having a peak value providing a measure of antigen concentration. The post-addition step is performed only if the peak rate value is ambiguous--, i.e. if it indicates one antigen concentration value for a reaction in antigen excess but another value for a reaction in antibody excess. The need for the post-addition step is determined from measured qualities of the rate signal including one or more of (1) the peak rate value, (2) the elapsed time from the start of the reaction to the peak rate, and (3) the product of the peak rate and the elapsed time. When required, the post-addition step may be performed during progress of the antigen-antibody reaction after measurement of the peak rate value.

Abstract: An optical concentration measuring apparatus and method which provides an output signal which is a substantially linear function of the concentration. The apparatus includes a chamber for containing a fluid sample and a source of optical radiation which develops a beam which is transmitted through the chamber and the sample. A first photoelectric cell is disposed to receive the transmitted beam for generating an electrical signal commensurate with the intensity of the beam after passage through the chamber and the fluid sample, and a second photoelectric cell which is disposed at a selected angle with respect to the direct beam for providing an electrical signal commensurate with the light scattered in a direction corresponding to the selected signal. The signal commensurate with the scattered beam and the signal commensurate with the direct beam are applied to a signal processor which develops a ratio of these signals, one of the signals being multiplied by a constant.

Abstract: Method and apparatus for determining the concentration of any of a wide range of antigen or antibody molecules with a high degree of specificity, accuracy and sensitivity. Antigen or antibody concentration is determined by effecting an agglutination reaction between carrier particles in a liquid medium, exposing the liquid medium to a beam of light, and measuring the ratio of the intensities of light scattered at two different angles as a function of antigen or antibody concentration. The unknown concentration of antibody or antigen is determined by comparison with similar measurements of the anisotropy ratio using known concentrations of the molecule being tested for. The agglutination reaction is performed using carrier particles coated with an agglutinant. The carrier particles should be fairly uniform in size and their diameter can be less than or comparable to the wavelength of light.

Abstract: A system for the detection of precipitate-forming antigens by means of the reaction with their corresponding antibodies is disclosed. The reaction of precipitate-forming antigens with their respective antibodies produces a precipitate in proportion to either the antibody concentration or the antigen concentration, depending on which is present in excess. The method does not require formation of actual precipitate, but measures the formation of "scattering centers" -- i.e., molecular aggregates of sufficient size to produce measurable scatter of light. The quantity of scattering centers formed is measured by nephelometric means and the measuring system performs an immunonephelometric analysis. In particular, the rate of change of the nephelometric signal with respect to time is measured and the peak rate and time to the peak rate established. From these simultaneous measurements both the antigen/antibody concentration and the condition of antibody or antigen excess are determined.

Abstract: Optical apparatus for measuring the amount of light reflected and/or scattered by particles suspended in a fluid, such as scrubber carryover appearing as a spray of dispersed water droplets. The amount of light reflected and/or scattered is an indication of the volume and mass of the suspended particles. A beam of light is caused to pass diagonally across a stream of purging gas used to keep the optical components clean and is directed onto the suspended particles at a point outside the purging gas stream. The light reflected back through the purging stream is then measured in intensity to determine the total volume of the particles from which mass may be determined. The invention overcomes the disadvantages of prior art devices in which the purging gas can disrupt the environment in which particle density is to be measured.

Abstract: Apparatus for the measurement of hair-like particles, such as measurement of the amount of asbestos fiber in air. Apparatus including a source of a polarized beam of radiation directed to a scattering zone and a detector for detecting radiation of the beam scattered from the zone. A device at the zone, typically a pair of spaced parallel plates with an electric field therebetween, for orienting the hair-like particles parallel with each other and substantially perpendicular to the incoming beam of radiation, and a drive mechanism for rotating the polarized beam relative to the oriented particles to a first position with the polarization of the beam parallel to the particles and to a second position with the polarization of the beam perpendicular to the particles.

Abstract: A condensation nuclei counter for measurement of the concentrations of Aitken particles in gases by measurement of light scattered in a cloud chamber by water droplets formed on the particles in successive samples of a gas wherein the counter provides for sequential high speed sampling of the photodetector output during the cloud chamber growth of the droplets of each gas sample tested as a way of measuring the rate of increase of total droplet cross-section and wherein the counter provides for automatic ranging for particle population coordinated with the timed sampling during particle growth.