156 Royal Irish Academy. 



Monday Evening, December 13, 1880. 

 SiE Samitel Feegttson, ll. d., in the Chair. - 



The Chairman declared the Ballot open, and asked Messrs. Porte 

 and Kane to act as Scrutineers. 



The Rev. J. H. Jellett detailed the results of experiments made 

 hy himself and George F. Fitzgerald, m.a., f.t.c.d., for the purpose 

 of ascertaining whether it be possible to detect any action of 

 a galvanic current on a beam of polarized light when transmitted 

 through air at the ordinary barometric pressure. Two grants had 

 been made some time ago by the Academy for the purpose of con- 

 ducting these experiments ; but various causes of delay intervened, 

 and the conclusive experiment was not made until Thursday last. The 

 details of the experiment are as follow : — 



A beam of solar light was polarized by a Mcol's prism. It was 

 then transmitted through a brass tube, round whi(;h a double coil of 

 insulated copper wire passed. On emerging from the tube the beam 

 was analyzed by a Jellett's prism, capable of showing a deviation of V 

 in the plane of polarization. A current obtained from a Gramm's 

 machine, driven by a gas engine, 3^ h. p., was transmitted through 

 the coil, and the analyzing prism was adjusted so as to give a perfect 

 equality of tint. The current was then reversed and the analyzer 

 observed. By this method, as is easily seen, the change in the plane 

 of polarization produced by the current would be doubled. But no 

 inequality of tints could be perceived. Hence it is to be inferred that 

 a current such as that here described is incapable of producing a 

 deviation of 30" in the plane of polarization of a transmitted beam. 

 The dimensions of the several parts of the apparatus were the fol- 

 lowing : — 



Length of tube, . . . 30-35 feet. 



Thickness of wire, ... '^"^ -096. 



Length of wire, . . . 1790 feet. 



Number of coils, . . . 5340. 



The Secretary read, for the Eev. J. Pearson, a Paper '' On Three 

 Years' Observations of the Tides at Liverpool (Fleetwood)." [Vide 

 Proceedings, vol. iii., ser. ii., Science, part 6.] 



