Royal Society. 371 



1 . Heat, whether luminous or obscure, is capable of polari- 

 zation by tourmaline. 



2. It may be polarized by refraction. 



3. It may be polarized by reflection. 



4. It may be depolarized by doubly refracting crystals. 

 Hence, 



5. It is capable of double refraction, and the two rays are 

 polarized. When suitably modified, these rays are capable 

 of interfering like those of light. 



6. The characteristic law of depolarization in the case of 

 light holds in that of heat, viz. that the intensities in rectan- 

 gular positions of the analysing plate, are complementary to 

 one another. 



7. As a necessary consequence of the above, confirmed by 

 experiment, heat is susceptible of circular and elliptic polari- 

 zation. 



8. The undulations of obscure heat are probably longer than 

 those of light. A method is pointed out for deducing their 

 length numerically. 



78. Of the evidence for these conclusions I have enabled 

 the reader to judge, by specifying numerical results. But I 

 must further add, that all the principal conclusions were ar- 

 rived at by the indications of the galvanometer, observed by 

 the naked eye, including the chief phaenomena of depolariza- 

 tion. Since I thought of the method of magnifying the divi- 

 sions (described in (5),) I had little else to perform than the 

 agreeable task of verifying and defining my first conclusions. 



Edinburgh, 19th January, 1835. 



LX. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



1835, A PAPER was read, entitled, " On the probable Posi- 

 Feb. 19. — -^ tion of the South Magnetic Pole." By Edward 

 Rudge, Esq., F.R.S., &c. 



The recent discovery of the site of the North Magnetic Pole, which 

 has resulted from the experiments of Capt. James Ross, suggested 

 to the author the inquiry whether any similar indications of an ap- 

 proach to the South Magnetic Pole can be gathered from any obser- 

 vations now on record. With this view a table is given of the obser- 

 vations made by Tasman in 1642 and 1643, during his voyage of 

 discovery in the Southern Ocean, extracted from his journal ; from 

 which it appears that he on one occasion noticed the continual agita- 

 tion of the horizontal needle, in south latitude 42° 25', and longitude 

 from Paris 1 60°. On the presumption that the South Magnetic Pole 

 was at that time near this spot, and that it has since been retrograd- 

 ing towards the East, the author conjectures that it will now be found 



3 B2 



