Abstract: Apparatus for monitoring gaseous pollutants (e.g. on a chemical plant) produces two infra-red laser beams having different wavelengths (one corresponding to an absorption line of the gas to be monitored, the other being a reference) which are modulated with different frequencies or phases, and then combined into a single scanning beam. The scanning beam is continuously displaced angularly so as to scan the area to be monitored. A portion of the beam is returned to the apparatus by scattering or reflection, and is measured. By correlating this with the direction of the beam, a plan of the monitored area superimposed with a continuously updated indication of the amount of gas can be displayed e.g. on a VDU.

Abstract: An electrostatic spraying nozzle, particularly for agricultural use, provides for a high rate of liquid delivery, up to 6 or 7 mL/s, while maintaining uniform charging of the atomized spray by means of a low-current supply. Atomization is produced centrifugally from a conical rotor and the liquid is charged by contact with an electrically isolated conductive coating on the surface of the rotor. The coating is raised to the potential of a high-voltage needle electrode by conduction through one or more air-gaps between the needle point and the conductive surface. The conductive surface is of sufficient extent in relation to the position of the electrode to shield the electrode from any external surface at earth potential and thus to ensure that only the required charging current is passed by the electrode. A shielding action is produced by a relatively deep conical form which also allows a high flow rate. For a frustro-conical surface of apical angle 60.degree. a ratio of end radii in the range 0.85 to 0.