Arrangement of the Apparatus.
The radiating apparatus and the receiver are mounted on stands sliding in an optical bench. Experiments are carried out with divergent or parallel beams of electric radiation. To obtain a parallel beam, a cylindrical lens[1] of sulphur or ebonite is mounted in a square tube. This lens-tube fits on the radiator-tube, and is stopped by a guide when the oscillatory spark is at the principal focal line of the lens. The radiator-tube is further provided with a series of diaphragms by which the amount of radiation may be varied.
Fig. 4.—Arrangement of the Apparatus. 110 nat. size.
R, the Radiator. T, the Tapping Key. S, the Spectrometer-Circle. M, the Plane Mirror. C, the Cylindrical Mirror. p, Totally Reflecting Prism. P, the Semi-Cylinders. K, the Crystal-Holder. F, the Collecting Funnel attached to the Spiral Spring Receiver. t, the Tangent Screw, by which the Receiver is rotated. V, Voltaic Cell. r, the Circular Rheostat. G, the Galvanometer.
For experiments requiring angular measurement, a spectrometer-circle is mounted on one of the sliding stands. The spectrometer carries a circular platform, on which the various reflectors, refractors, &c. are placed. The platform carries an index, and can rotate independently of the circle on which it is mounted. The receiver is carried on a radial arm (provided with an index) and points to the centre of the circle. An observing telescope may also be used with an objective made of ebonite with a linear receiver at the focal plane. But an ordinary receiver provided with a funnel is all that is necessary for ordinary experiments.
- ↑ See Lodge and Howard, Phil. Mag. July 1889.
