Jagadish Chandra Bose

“ For the accurate measurement of deviation, the effect produced by radiation on the receiver should undergo an abrupt variation. When the radiation passes from a dense to a light medium, at a certain critical angle of incidence, the radiation is totally reflected. ”

“ The Refracting Substance.—For substances which can be cast, the molten mass is poured into a cylindrical mould with a thin partition in the middle. In this way two equal semi-cylinders are obtained at each casting. Substances like wood or stone are turned, and the cylinder sawn into two equal halves. In my experiments different sized cylinders were used. I have successfully used small ones with a radius of 8 cm. only. But when the cost of the material is not prohibitive, it is advisable to use fairly large cylinders. The cylinders used in the following experiments were 27·4 cm. ”

“ The angle of incidence is thus gradually increased, till the rays just undergo total reflection. When this is the case the receiver ceases to respond. Let A be the corresponding reading of the platform index. A stationary index I′ is now placed opposite the reading A of the graduated circle. When the cylinder is rotated in the opposite direction a second reading B for the critical angle is obtained. It is obvious that, neglecting errors, A–B is equal to twice the critical angle.
The platform index is now clamped and the circle as a whole is rotated till B comes opposite to the fixed index I′. ”