Page:Collected Physical Papers.djvu/94

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One of the strongest polarising substances I have come across is the crystal epidote. The crystal I have, is very small in size, and I could not get with it complete absorption of one of the two rays. But it exhibits very strong depolarisation effect, even with a thickness as small as 0·7 cm. This is, undoubtedly, due to strong selective absorption in one direction. I cut a square from this crystal 0·7 × 0·7 cm. with a thickness of 0·4 cm. Using an E. M. F. of 14 volts the deflections obtained (proportional to the two conductivities) were 105 and 20 divisions respectively. The conductivities in the two directions