220 R. Straubel : Experiments on the 



about 6 h the differences E — W were even less. The com- 

 parison of the two hours serves to check possible errors, 

 e. g. of a magnetic character, such as might be caused by the 

 magnetism of the Ruhmkorff coil, if insufficiently distant. 



It seems certain that at neither hour does the difference 

 E — W actually amount to ^L f a degree, i. e. to * of 

 the whole rotation. In all probability the influence of the 

 reversal is much less, if indeed it exists at all. 



P.S. — Since the above observations were made, I see from 

 the Amsterdam Proceedings (May 28, 1902) that Lorentz 

 maintains his opinion against the criticism of Larmor. 

 Lorentz 's theoretical result contains an unknown quantity 

 which might be adjusted so as to make the influence of the 

 earth's motion evanescent ; but for this special adjustment 

 there appears to be no theoretical reason. I hope that the 

 above experimental demonstration of the absence of effect, 

 to a high order of accuracy, will be found all the more 

 interesting. 



XXIII. Experiments on the Electro-thermal Effect in 

 Tourmaline. By R. Straubel"*. 



AS was first shown by W. Thomson in 1877, from thermo- 

 dynamical considerations, there corresponds to the 

 pyro-electric phenomenon — i. e. the electrification produced 

 by a uniform rise of temperature — a reverse effect, namely, a 

 temperature change due to a variation of the electric state. 

 If a pyro-electric crystal be brought into an electric field so 

 that the lines of force run from the analogous to the anti- 

 logous pole, it will be heated ; if the orientation of the crystal 

 in the field is reversed, a cooling will take place. 



On the effect so predicted by theory 1 carried out some 

 experiments about two years ago, using a Brazilian tourma- 

 line. These experiments, though only qualitative, will be 

 briefly described in what follows. 



Four plates, each 0'2 cm. thick, were cut from the tour- 

 maline crystal in a direction normal to its axis. The plates 

 were then arranged in two pairs, in one of which the ana- 

 logous poles, and in the other the antilogous poles, were 

 uppermost. Between the plates of each pair was introduced 

 one set of junctions of a home-made thermopile of ten 

 elements, made of fine wires of constantan and iron. The 



* Translated from the Nachrichten der K. Gesellschaft der Wissen- 

 schaftenzuGottingen,Mathematisch-physikalischeKlasse. " 1902. Heft 2. 



