Jagadish Chandra Bose

“ It is very troublesome, in the middle of an experiment, to be obliged to take out the radiator for polishing. The flash of radiation produced by a single break is enough for an experiment, and it is a mere waste to have a series of useless oscillations. In my apparatus for quantitative measurements I have therefore discarded the vibrating interrupter in favour of a simple break-key. ”

“ The funnel has two hinged side-doors, by which its area—and, therefore, the amount of radiation collected—may be varied. When angular deviation is to be measured, the doors are made parallel and perpendicular to the layer of spirals. The aperture is reduced, and the receiver then only responds when the funnel points to the direction of the deviated ray.
In polarization experiments it is necessary to adjust the receiver carrying the analyser in a crossed position. This is done by a tangent screw, the rotation of the analyser being measured by means of an index and a graduated vertical disk. ”

“ An electric current enters along the breadth of the top spiral and leaves by the lowest spiral, having to traverse the intermediate spirals along the numerous points of contact. The resistance of the receiving circuit is thus almost entirely concentrated at the sensitive contact-surface, there being little useless short-circuiting by the mass of the conducting layer. When electric radiation is absorbed by the sensitive surface, there is a sudden diminution of the resistance and the galvanometer spot is violently deflected. ”

“ The difficulty was still further enhanced when the radiator and the receiver had to be enclosed in narrow tubes to enable angular measurements to be made with any accuracy. It seemed to me that the frequent loss of sensibility might be due to the particles getting jammed together, and the fatigued condition of contact surfaces. In order to avoid this I used a layer of narrow spirals of steel, lying side by side, and rolling on a smooth surface. The points of contact are numerous, and fresh surfaces can be brought into action by a slight rolling of the spirals. ”

“ Electric oscillation is produced by sparking between two beads of platinum and an interposed sphere of the same metal. The discharge ceases to be oscillatory when the ball is roughened, and a platinum ball resists, to a great extent, the disintegrating action of the sparks. ”

“ The index of refraction of commercial sulphur is = 1·73; that of a specimen of pitch = 1·48.
Indices for Liquids.—A cylindrical trough is filled with the given liquid; two thin parallel glass plates enclosing an air-space are vertically placed so as to divide the liquid cylinder into two halves. The readings for total reflexion are taken as in the last case. The index for a specimen of coal-tar I found to be 1·32.
Selective Absorption.
A substance is said to be coloured when it allows light of one kind to pass through, but absorbs light of a different kind. ”

“ A fairly thick piece completely absorbs vibrations parallel to the fibres, and transmits vibrations perpendicular to the fibres. Ordinary radiation, after transmission through a thick piece of serpentine, would be plane-polarized, the vibration taking place perpendicular to the fibres. A thick piece of serpentine thus acts as an efficient polarizer. ”