Abstract: A machine tool for sequentially machining workpieces with different tools which may be clamped in a spindle of the machine tool, comprising a magazine in which the tools are disposed in a ring pattern and held in holders such that the holder of the tool to be clamped in or unclamped and removed from the spindle is in alignment with the spindle axis during the tool change, is characterized in that the holders of the magazine are distributed about the spindle axis, that each holder is provided with its own drive which moves it into a position where it is aligned with the spindle axis (clamping position) and into a position outside the spindle axis (magazine position) and that the holder remains aligned with the spindle axis while the tool held therein performs a machining operation. This permits a very quick tool change.

Abstract: A multilayer structure comprising a Si layer/ a refractory metal oxide layer/ a refractory metal layer/ is subjected to annealing in an atmosphere of hydrogen or an inert gas mixed with hydrogen, thereby converting the multilayer structure into a multilayer structure comprising a Si layer/an inner SiO.sub.2 layer formed by internal oxidation of Si/a refractory metal layer. The inner SiO.sub.2 layer is selectively formed only on the surface of the refractory metal layer, since Si is internally oxidized from the side of the refractory metal layer. In case of gate electrode of a MISFET, the gate electrode and a contact hole for source or drain electrode are positioned in self-alignment with each other via the inner SiO.sub.2 layer. The distance between the gate electrode and the source or drain electrode is determined by the thickness of the inner SiO.sub.2 layer. A semiconductor device with a high density and a high speed is realized.

Abstract: A solar cell fabrication procedure is described in which a hydrogen ion passivation step is used to form, inter alia, an altered silicon substrate surface layer to which immersion plated nickel will not readily adhere. The altered surface layer is formed by shadow casting an ion beam in a pattern corresponding to the desired front surface interelectrode configuration.

Abstract: A polyphase winding of ladder-like configuration for a linear motor is installed into a prearranged inductor assembly having a plurality of parallely arranged grooves, the inductor being attached to the underside of a T-shaped type carrier; a vehicle runs on that carrier carrying a drum for storing the winding (cable assembly), and there is a deflection system which runs the winding from the drum towards the underside of the carrier in near-tangential disposition whereby a tool resiliently mounted on an outrigger causes rungs of the ladder to be sequentially forced into the grooves of the inductor and, possibly, locked therein.

Abstract: A method of manufacturing transformer cores of either the continuously wound or cut wound type using electrical steel strip having approximately a linear taper. By selecting a suitable taper, a hexagonal (or higher order) approximation of a circular cross section for the legs of the cores is produced. Two complementary core strips can be cut from a single rectangular stock strip in a scrapless manner. The product produced by the method is also disclosed.

Abstract: An apparatus for accurately aligning an information-containing-disc stylus and assembling the stylus to a stylus holder. The apparatus transfers the stylus from a magazine holding a plurality of such styli into a rotary collet which is then rotated by an operator until a laser beam of light is reflected off a known surface of the stylus and impinges on a fixed target. The apparatus then causes the point of the stylus to pierce the stylus holder to a specific depth whereby the stylus is held firmly by the stylus holder.

Abstract: Apparatus for securing a set of beams on a stationary assembly for a dynamoelectric machine. The apparatus has means for locating one end frame with an opposite end of at least one beam being seated thereon with tabs on the opposite ends of the beams being received in apertures of the end frame in spaced apart relation therefrom, respectively. Means is provided for biasing another end frame against the other opposite ends of the beams with tabs thereon being received in other apertures in the other end frame in spaced apart relation therefrom, respectively. Means is for simultaneously welding at least a part of the tabs to a part of the one and another end frame, respectively.

Abstract: Automatic system and method for compressing coil turns and insulators in stator core slots. Stator cores initially provided with end cuffed slot liners and a set of loosely inserted windings are loaded by the system operator sequentially into holding stations in a circular indexing, rotatable worktable. Each holding station comprises a cuff support assembly that serves simultaneously to precisely position and irremovably hold the stator cores as the worktable indexes the cores through a plurality of work stations. Automatic apparatus is provided at the work stations to initially press the turns into the slots, insert phase insulators, insert slot separator wedge insulators and further compress both the coil turns and insulators in the slots. A plurality of phase insulator work stations are gang operated to maintain high speed production rates despite relatively slow reloading of phase insulators into the insertion arbor of each work station.

Abstract: A plurality of electrically conductive heads for bending the leads of components mounted on a printed circuit board are coupled to an apparatus for testing the component prior to bending and soldering the leads. The heads electrically contact the leads of the component prior to and during bending. A testing apparatus indicates that the component is present and can also test one or more electrical parameters of the component. The test apparatus indicates whether the component is good or bad prior to the bending of the component leads to facilitate replacing the component before it is soldered in place.

Abstract: A clinching plate for supporting a circuit board to be loaded with electrical connectors by means of a robot or a pick-and-place machine, comprises a plurality of clinching units set in openings in the plate. The units comprise pairs of slides having clinching ears for clinching a pair of posts at each end of each connector to the board to hold the connectors in place while the board is transported to a soldering station. One clinching unit is provided for each connector and each unit is operated by means of an individual drive cylinder under the control of the microprocessor of the mother machine.

Abstract: Apparatus for applying insulating sleeves to electrical terminals, comprises a frame having a horizontal surface on which is a terminal locator for locating in front of a sleeve applicator ram, a terminal on a lead transported horizontally by a conveyor. A lead capturing and terminal positioning member is moved towards the terminal locator to position the terminal therein and the applicator ram is advanced to apply a sleeve to the terminal. When the sleeve has been applied to the terminal by means of the ram and the ram has been retracted, an ejector throws the terminal with the sleeve thereon, vertically out of the terminal locator, and a sleeve feed ram feeds a further sleeve between the applicator ram and the terminal locator. The above operations take place during a dwell period of the conveyor.

Abstract: An automatic wire end arranging system includes a wire holder for holding one ends of the wires, a wire feed device for feeding the wire ends one by one from the wire holder, and a transport device for transporting each wire end from the wire feed device to an arranging device. The arranging device includes a fixture having a plurality of parallel receptive sections, and a table mounted adjacent to the fixture and having a slit, a probe device operable to make electrical contact with the wire end, fed to the table by the transport device, to feed a probe signal, a first drive device operable to move the table, a second drive device operable to bring the wire end on the table into alignment with the slit, and a third drive device operable to urge the wire end, disposed in alignment with the slit, into a selected one of the receptive sections through the slit.

Abstract: Molded case circuit breakers having rear mounted line connectors are provided with retainer clips and plates to prevent easy removal of the breakers from electric panel box load stab connectors. The breakers can be removed for replacement however, without disassembling the entire electrical panel box.

Abstract: A tool for automatically assembling electrical terminals with a box insulator comprising a piston-activated jaws assembly for securing a wire in place in a work station so that press-driven tools can crimp the wire to a metal connector, after which a piston-activated slide forces an insulated box over the metal connector and its crimped connection thereby completing the assembly.

Abstract: A hand tool for cleaving optical fibers including an elongated body having a longitudinal axis extending lengthwise thereof. A fiber support surface is attached to the body and extends in a plane which is transverse to such longitudinal axis. Fiber clamping means are provided which are pivotally attached to the body for clamping or holding the optical fiber in place upon the fiber support surface and for subjecting the optical fiber to tension. Cutting means are also attached to the body and are moveable in the general direction of such longitudinal axis towards the fiber support surface for severing such optical fiber such that the end face of the fiber is smooth and lies in a plane perpendicular to the axis of the fiber.

Abstract: A hair cutter for thinning hair which includes a stationary blade, a movable blade, a comb member adjacent to either the movable blade or stationary blade, and a hair pressing member disposed on the side of either the stationary blade or movable blade where the comb member is not located. This arrangement permits hair to be thinned easily and accurately even when used by individuals lacking a barber's hair cutting skill.

Abstract: The invention relates to a cutting machine, in particular a fabric cutting machine, comprising a bearing table for the material and a supporting structure, which is displaceable along the table, for a cutting tool rotatable about a vertical axis and comprising drive means for driving the cutting tool relative to the table. In the case of a cutting machine of this type the invention has a first angular position detector associated with the cutting tool, this first angular position detector generating signals corresponding to the angular position of the cutting tool. In addition, a guide handle is provided on the cutting tool, this handle having associated signal generating means for producing additional control signals such that, on the basis of the signals from the first angular position detector and the additional signal generating means, control signals may be generated for the drive means of the cutting tool, which enable the cutting procedure to be servo-assisted when the cutting tool is guided by hand.

Abstract: A mowing machine is provided with its cutting head employing one or more flexible cutting lines such as Nylon cords which serve to cut grasses during rotation of the cutting head. The free end portions of the cutting lines extend radially outwardly from a casing through openings in an annular inertia shifter which is housed in the casing for vertical and angular movements relative to the casing.

Abstract: A mushroom slicer. An open-ended cylindrical tube has at least one lengthwise slot therethrough and a rectangular opening spaced from the slot. At one end is a cutter comprising a series of parallel wire passes across the tube adjacent that end. A piston freely movable inside the tube has a handle attached to it and extending out through the slot. In operation, a mushroom is placed via the rectangular opening into the tube between the piston and the cutter. The piston is rapidly moved manually toward the cutter to propel the mushroom through the cutter.

Abstract: A chain saw bar having a central groove along the top and bottom edges to guide the chain about the bar, and a bar nose structure at the end of the bar to guide the chain from the top edge to the bottom edge. The nose structure including an extension of the bar on one side of the groove and a roller rotatably mounted on the extension to form the other side of the groove at the nose of the bar. The roller and extension having arcuate peripheral faces to guide the chain about the nose of the bar.

Abstract: The present invention relates to a rainbow image projector adapted to project a vivid rainbow image from a relatively small light source onto walls of a stage, a store, places for various parties, and like. Specifically, light rays emitted from the linear incandescent light source are converted by a cylindrical condenser lens into parallel light rays which are, in turn, obliquely incident on a triangular prism over whole area of its first refraction plane. Thus, it is possible to project a vivid rainbow image of a large curvature radius from the small light source of small power consumption and heat generation. A housing containing therein said linear light source, cylindrical condenser lens and prism and provided with a projection window is inclination-adjustably mounted an inclination adjustment screw on a support leg so that a direction in which the rainbow image is projected may be variable.

Abstract: An electronic angle indicator providing a digital indication for a desired angle comprises a pivotally suspended gravity responding pendulum retaining a ring magnet, a reference angle dial retaining a ring magnet and two magnetic field sensors, one for sensing magnetic field change of said pendulum and the other one for sensing magnetic field change of said reference angle dial. The output of said pendulum magnetic field sensor is compared with the output of said reference angle dial magnetic field sensor and causes the indicators display attainment of a desired angle orientation selected by said reference angle dial, or greater or lesser angle than the angle orientation selected by said reference angle dial.

Abstract: A stream dryer comprises in addition to the control bypass which bypasses the heat source a second ready-use bypass which is in parallel with the control bypass and bypasses the heat source. In the event of short-duration interruptions in working, the supply of steam is interrupted and the circulation of the hot gas is maintained substantially only through the ready-use bypass, so that the temperature of the circulated hot gas substantially does not change when the relatively small heat losses due to surface and exhaust gas losses are compensated. Temperature regulation is effected through the agency of the control bypass in this state of readiness also.

Abstract: A drum type laundry dryer has an outer frame, a drying drum rotatably supported by the outer frame and adapted to receive laundry to be dried, a fan for introducing air into the drying drum, a heater for heating air to be introduced into the drying drum, air outlet ports in the drying drum and a filter device adjacent to the air outlet ports. The filter device is formed by a net and a lint collector disposed in opposite relationship to the net. The lint collector is annular and spaced from the net a distance which is smaller in the inlet section of the lint collector than in an inner section thereof.

Abstract: An athletic shoe having a sole bottom which is contoured in the region of first foot strike along the lateral border to provide an arcuate landing surface which curves upwardly toward the lateral side edge of the sole and away from the ground surface and which is radiused about an axis coinciding with an effective, average subtalar axis. The sole may additionally be contoured along the rear heel portion in the region of first foot strike for straight heel strikers to provide another arcuate landing surface which curves upwardly toward the rear edge of the sole and which is radiused about a transverse axis coinciding with an average ankle axis. The sole bottom is formed with separate sets of gripping ribs which are oriented in such a manner that traction is enhanced for a range of toe out angles in the toe off range, is maximized for an average toe out angle along the lateral border and is maximized for a zero toe out angle in the rear heel region.

Abstract: An insole for a sports shoe comprises an insole body of foam synthetic resin having recesses formed therein at the forefoot and heel areas. Corresponding pieces are of material having higher durometer hardness than that of the insole body and inserted in the recesses to provide good properties required for various kinds of sports.

Abstract: According to the invention a boot is provided which includes a shell base having an inner sole mounted therein. Additionally, the boot includes a foot retention system positioned within the shell base; the foot retention system including at least one support element positioned between the shell base and the area in which a foot is to be inserted. The support element is adapted to at least partially cover the foot. An adjustable tightening apparatus serves to tighten the support element around the foot. The tightening apparatus includes pressurization means for pressing the support element against the foot and adjustment means for adjusting the pressurization means. The boot apparatus is such that the pressurization means exerts pressure directly on a front portion of the foot, and extends generally from the inner sole of the boot to the upper portion of the foot.

Abstract: A form-fitting cover for use on an ironing board having nose and heel envelopes formed with a pad sheet attached to the lower surface of an ironing surface sheet whereby the ironing surface sheet is automatically properly positioned when the nose and heel envelopes are fitted onto the ironing board.

Abstract: A sign holder for a packet of planar members bearing characters for display. Deformable material having a sheet portion has a pocket for receipt of the packet. The pocket has a front retaining wall formed from the sheet portion to prevent the packet from moving out of the pocket in a front direction. The pocket also has, pressed from the sheet portion in a direction away from the front direction, the following: First and second opposed and spaced apart side walls, and a third side wall located in the pocket intermediate the first and second side walls. The first, second and third side walls retain the packet in directions transverse to the front direction. First, second and third backing walls are connected, respectively, to the first, second and third side walls. The first, second and third backing walls inhibit movement of the packet in a direction opposite to the front direction. At least one gap substantially separates the first, second and third backing walls from each other.

Abstract: A plastic display card holder for receiving and gripping a card for display purposes comprises interconnected spaced-apart parallel wall portions. The wall portions are connected in a manner to provide an entrance for insertion of a display card. A plurality of resilient plastic projections are provided on the holder which flex as the display card is inserted into the holder through the entrance. The flexed projections grip the inserted display card as the resilient projections attempt to recover to their normal unflexed position.

Abstract: An improved fishhook and lure includes strands of serrated sharp toothed filaments or similar material adjacent the hookeye, extending in a trailing direction coveringly around the shank and barb of the hook. Each of the serrated filaments presents a repeated extension of barbed teeth, where the barbs point toward the eye of the hook. The reversed engaging barbed sections on each of the filaments are flexible but have a relatively sharp edge and point. When the lure is engulfed by the mouth of a fish the action of the plurality of barbs will retard disgorgement and cause the lure to be readily ingested, so that the main hook will be ingested by the fish and may then be set. The improved fish lure will primarily be for still fishing, trot-line fishing or long line fishing; it may also be cast.

Abstract: A trapping device is disclosed for animals such as rats, mice and other types of animals. One particular design disclosed herein entails a tomb type trap especially designed for rats and mice which is disposable and of a simple and inexpensive monolithic or integral construction. This trap includes a spring loaded conical door that is actuated by the animal itself to move to a closed position and which effectively seals the disposable trap and causes the rats, mice or other animals to suffocate. Once the animal is trapped within the tomb type trap, the same may be discarded.

Abstract: An animal trap comprising an elongated housing having open and closed ends, a door pivotally mounted at its lower end on the housing adjacent the open end and movable between an upright closed position wherein it closes the open end and an open position wherein it is disposed within the housing in a substantially laterally extending position near the bottom of the housing. The door is biased to the closed position. A panel is pivotally connected at one end to the housing and extends generally laterally within the housing near the bottom thereof toward the closed end. An elongated pawl member is pivotally connected at one end with the adjacent end of the panel opposite to the one end thereof, and is pivotally connected at its opposite end to the housing. The pawl member has a tooth at its opposite end and is urged in an upward direction. The tooth is positioned to engage the door when it is moved to the open position to retain the door in the open position.

Abstract: A padded leghold trap of the pivoting jaw type includes recessed portions of the jaws in which respective pads are disposed. The pads each have concave facing surfaces with an inner edge that barely touches the inner edge of the other pad in the sprung position of the jaws, leaving the remainder of the concave facing surfaces mutually spaced. A trapped animal is held between the padded jaws which spring closed and traps the animal's leg without breaking the leg or causing edema. Attempts by the trapped animal to pull its trapped limb from between the jaws causes the radially inner pad edges to roll over toward the limb and thereby increase the retention forces. A retainer for the pad is disposed over an access slot in the pad, which access slot is provided to deploy the pad on the jaw. The retainer includes a bent lip which deforms the pad toward the jaw to prevent the pad from being pulled off the jaw by a trapped animal.

Abstract: An insect trap arrangement, kit therefor and method of making the same are provided, the trap arrangement comprising a lure unit for attracting insects thereto and causing the attracted insects to fall by gravity therefrom, an insect storage container having an inlet for receiving the falling insects therethrough whereby the storage container is adapted to store the falling insects therein, and a conveying unit disposed intermediate the lure unit and the storage container and having an inlet operatively associated with the lure unit to receive the falling insects therefrom and having an outlet operatively associated with the inlet of the storage container for discharging by gravity the falling insects from the conveying unit into the inlet of the storage container.

Abstract: An inner plant pot for holding a living plant, soil and hydrophilic inert material and supported within an outer container. Openings in the bottom and side of the plant pot provide passages for water and air to a large area of the roots of the plant.The inner and outer containers are dimensioned to provide minimal water storage. Water is forced into the inner container through openings and the water is retained by the inert material and the soil.

Abstract: A watering and feeding system for plants, comprising a container enclosing a platformed water reservoir, housing a water supply unit, a fertilizer dispensing unit, a nutrient conveying wick and a water level indicator unit, all of which are interacting to provide automatic and adequately measured amounts of nutrients to the plants, embedded in soil on top of the platformed water reservoir.

Abstract: In a door arrangement (20) for the control panel (14) of an apparatus (12) with a door leaf (26) movable by motor, on the inside of which leaf a sensing arrangement is arranged, the sensing element is formed by a contact strip (40) extending over the total length of the closing edge (30) of the door leaf (26), which strip is movably guided on the inside of the door leaf at an acute angle .alpha. to the plane of the door leaf in such a way that in its first position it at least approximately touches or intersects the plane of the outer face (26) of the door leaf. The contact strip (40) is guided in a guide strip (32) which extends over the total length of the closing edge (30) and is fastened to the door leaf (26), which guide strip shows a guide groove (38) for receiving the contact strip (40).

Abstract: The present invention concerns a revolving door device having arcuate screens arranged on diametrically opposite sides of the passage space constituting part of the revolving door closely adapted to the fixed outer walls of the device. Said screens being connected with each other through a partition wall divided up in three sections having the central section openable. The respective outer sections is aligned along a chord of the circular space so that when said screens are in a position for access to the respective passage spaces, a free through path may be obtained from entrance opening to the outer through the openable central section in case of emergency.

Abstract: The undulate cutting edges of knives on a rotary knife holder in a tobacco shredding machine are ground by a grinding wheel whose profile is complementary to that of the cutting edges and which is moved stepwise in parallelism with the axis of the holder and thereupon radially or tangentially of the holder toward and from engagement with successive portions of the knives so that the grinding wheel treats a portion of a previously treated section and an untreated section of each knife while it is held close to the path of orbital movement of the knives. An advancing mechanism is provided to shift the grinding wheel stepwise in parallelism with the axis of the holder, and a moving mechanism is provided to displace the grinding wheel toward and away from the path of orbital movement of the knives during each interval between successive advances.

Abstract: An apparatus for shaping a three-dimensional workpiece by inducing the following relative motions between an abrading die member and the workpiece: a feed motion, periodical retract and advance motions in a z-direction, and a planetary or orbital motion in the x and y directions. The mechanism which generates the planetary or orbital motion is provided with means for infinitely adjusting the eccentricity of this motion and is provided with means for selectively and releasably fixing the chosen amount of eccentricity. An assembly is provided to adapt the following process values to conditions within a gap between the die and the workpiece such that the abrading process is optimized: (i) feed pressure between the die and the workpiece during an abrading period of a work cycle; (ii) speed of the feed motion; and (iii) speeds of periodical retract and advance motions.

Abstract: The machine grinds the rims of spectacle lenses in accordance with data from an electronic data memory containing the circumferential configuration of the spectacle lens. The grinding machine is controlled by a computer.

Abstract: An optical projection profile-grinding machine with a workpiece holder that accepts the workpiece to be machined, a grinding wheel that may be positioned in relation to the workpiece, a projector for displaying an enlarged image of the point of engagement between the workpiece and grinding wheel on a projection screen, and a nominal profile line arranged on the projection screen, characterized by the workpiece being capable of rotation around the optical axis of the projector and of fixation in different angular positions in unison with the projection screen and its nominal profile line. The projection screen, or a carrier screen that accepts a nominal profile line and is arranged on the projection screen, is rotatable around the optical axis of the projector, in synchrony and at the same angular velocity as the workpiece.

Abstract: The grinding wheel is first dressed by a dressing tool and is thereupon sharpened or finished by particulate material which is introduced into a gap between its working surface and a pressure applying roll. The latter is thereupon ground by the grinding wheel. The controls of the grinding machine are used to feed the grinding wheel toward the dressing tool and the roll to different extents in order to compensate for the fact or possibility that the wear upon the roll during finishing is or can be more pronounced than the wear upon the dressing tool during dressing of the grinding wheel. This also ensures that the width of the gap can be maintained at a given value during each of several successive finishing operations.

Abstract: Apparatus for blast-cleaning the interior surface of a pipe includes a main housing that travels the length of the pipe, and rotatably supports a blast nozzle. A nozzle support shaft carried by the housing rotates freely, reactively to air carrying abrasive media and forced through the nozzle under high pressure. Since the air is directed through a non-rotating conduit to the shaft, a gasket is interposed between the rotating and non-rotating components. To prevent the abrasive media from penetrating the shaft support bearings of the housing with obviously destructive effects, a gap is maintained between the housing and a junction housing in which the non-rotating conduit is mounted. Leakage that does occur past the gasket is dispersed to the ambient atmosphere through the gap, before it can impinge upon the bearings. The non-rotating conduit is threadedly advanceable within the junction housing, so as to correspondingly, selectively adjust the extent to which the gasket is compressed.

Abstract: Improved automatic seating for a telescopic system includes stancheons for mounting individual chairs. Each stancheon includes forward and rear frame members which are pivotally mounted to a bracket and arranged to pivot between a raised use position when the rows are extended and a lowered storage position when the rows are retracted for storage. A coil spring is connected between the stancheon frame members and biases them to the raised position so that the seating raises automatically when the rows are extended for use. Each stancheon is secured in the raised position by a self-tightening latching mechanism which is actuated independently of all other stancheon latches so as to compensate for tolerances in an individual stancheon assembly and to latch it securely in the use position, whereas all latches are disengaged in unison by movement of the next lower row to its storage position.

Abstract: A roofing structure is disclosed having a layer of blocks of insulating material supported on a roof deck and featuring a hermetic seal encapsulating a limited part of the insulating material layer and which completely envelopes selected insulation blocks covering at least portions of the deck periphery to effect wind uplift resistance.

Abstract: Apparatus for covering relatively wider building structure expansion voids which includes a cover panel, base member extrusions for opposite side support and a lazy tong centering assembly for both supportive attachment to the cover panel and maintaining proper alignment and relative positioning to said void in tolerance of orthogonal relative displacements between adjacent structures.

Abstract: In an extensible arm having a reticular lattice structure with a polygonal cross-section, particularly for space modules or vehicles, each longitudinal side of the lattice structure includes first and second kinematic pantograph chains each constituted by a plurality of rods articulated together so as to define a series of aligned X-shaped elements. The rods of the second kinematic chain are shorter than the rods of the first kinematic chain, and the articulations between the X-shaped elements of the second kinematic chain located on one side of the latter coincide with the articulations between the X-shaped elements of the first kinematic chain located on the same side.

Abstract: Energy efficient houses are built with concrete outer walls underground in thermal contact with the earth temperature, which is at a comfortable level for human use and varies little from summer to winter. Thus, the inner concrete walls are made active energy transfer surfaces of a year around temperature control system, which in its simplest form comprises a fan circulating interior building air in a thermal exchange relationship over substantially the entire concrete inner wall surface. For even better thermal efficiency, the outer concrete walls are thermally insulated on the upper portions nearer the earth's surface, where a larger variation of temperature is encountered from summer to winter. Therefore the entire inner concrete wall thermal exchange surface may be kept typically at a temperature of 77 degrees F plus or minus 2 degrees throughout the year and thus constitute a most efficient primary source of thermal energy.