Page:Collected Physical Papers.djvu/93

Rh It will thus be seen that the direction of absorption is also the direction of greatest conductivity, and the direction of transmission is the direction of least conductivity.

My anticipations being thus verified, I proceeded to make further measurements with other specimens. From the perfect specimen of nemalite in my possession, I cut two square pieces, A and B. The size of piece A is 2·56 × 2·56 cm., with a thickness of 1·1 cm.; B is 2·76 × 2·76 × 1·2 cm.

For the determination of resistances I used a sensitive Kelvin galvanometer, having a resistance of 7000 ohms. With three Leclanché cells, 1·4 volt each, and an interposed resistance equivalent to 55,524 megohms, a deflection of 1 division in the scale reading was obtained. The table below gives the results of the measurements which I carried out. They clearly show how the difference of absorption in the two directions is related to the corresponding difference in conductivity.

I then proceeded to make measurements with chrysotile. The specimens I could obtain were not very good. I cut two from the same piece, and a third specimen was obtained from a different variety. The ratios of conductivities found in the three specimens were 1 : 10, 1 : 9, and 1 : 4 respectively. In every case the direction of absorption was found to be the direction of maximum conductivity.

A fibrous variety of gypsum (CaSO4), popularly known as satinspar, also exhibits double absorption; and in this case, too, the conductivity in the direction of absorption is found to be very much greater than in that of transmission.