TRANSACTIONS OF SECTION A. 725 
4, On a Complete Apparatus for the Study of the Properties of Electric Waves. 
By Professor JaAGADIs CHuNDER Boss, I.A., D.Sc. 
A complete electro-magnetic radiation apparatus was exhibited with which the 
following determinations may be made :— 
A. Verification of the laws of reflection. 
1. Plane mirrors. 
2. Curved mirrors. 
B. Phenomena of refraction. 
]. Prisms. 
2. Total reflection. 
3. Opacity caused by multiple refraction and reflection. 
4, Determination of the indices of refraction. 
C. Selective absorption. 
1, Electrically coloured media. 
D. Phenomena of interference. 
E. Double refraction and polarisation. 
1. Polarising gratings, 
2. on crystals. 
3. Double refraction produced by crystals. 
4. A y other substances. 
5. a " strain. 
Ms Need aioe eas 4 Experiments still in progress. 
8. Electro-polariscope and polarimeter. 
The complete apparatus consists of (1) A radiating apparatus emitting electric 
waves of short length ; (2) A receiver used as a detector of electric radiation ; and 
(8) Various accessories for the study of the different phenomena. 
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 beam of electric radiation. To obtain a parallel beam, a 
cylindrical lens 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. 
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. 
5. Report on Meteorological Observations on Ben Nevis. 
See Reports, p. 166. 
6. Report on Solar Radiation.—See Reports, p. 241. 
7. Report on Seismological Observations.—See Reports, p. 180. 
8. Report on Meteorological Photographs.—See Reports, p. 172. 
