1835.] the Advancement of Science, 213 



great velocities. He exhibited a table of results, and de- 

 duced from it that the difference in different canals accord- 

 ing to size and depth, is dependent on the velocity of the 

 wave raised. A member stated that the results are con- 

 firmed on two canals in Ireland, but gave a somewhat 

 different explanation. Another member confirmed the 

 results. 



Wednesday, \2th August. — 12. Mr. Pritchard exhibited 

 some experiments on polarization, this morning before the 

 meeting; they consisted chiefly of improvements in the 

 mode of exhibition. The most singular fact shewn was, the 

 formation of a certain white elliptic ring, by light passing 

 through calcareous spar. 



13. Mr. Snow Harris on the use of the proof plane, and tor- 

 sion balance of Coulomb and others. He detected consider- 

 able differences in the distribution of electricity in different 

 parts of bodies, and obtained results, apparently at variance 

 with Poisson's theory. He compared various theories, and 

 exhibited experiments in support of his views. Mr. Whe- 

 well made some remarks on the experiments of Mr. Harris, 

 and on the utility of theories to assign causes. He differed 

 from Mr. Harris as to the inferences from the experiments, 

 and showed, that many of the supposed exceptions are really 

 quite accordant with the mathematical theory. 



14. Captain Sabine gave an account of Hansteen's re- 

 searches on terrestrial magnetism, who had collected obser- 

 vations on the variation of the needle in different parts of 

 the globe, and demonstrated that there are two magnetic 

 poles in each hemisphere. He exhibited maps of the varia- 

 tion at different dates, and shewed that the line of no dip was 

 not a great circle but inflected. He noticed the excursion 

 of Hansteen to determine the magnetic poles, and variation 

 in Siberia, the observations of Captain Ross and others, 

 and concluded by remarking, the absence of any data for 

 determining the position of the southern pole. 



15. Professor Wheatstone examined with a prism the line 

 of light formed by the voltaic spark between charcoal 

 points. The spectrum was complete without interruption, 

 but marked by certain lines of more intense brightness. 



With the electric light from a surface of mercury, a few 

 very bright lines of definite colour appeared separated by 

 wide dark intervals. 



