British Association for the Advancement of Science. 293 



polarity above mentioned. The reason of this is, that the more 

 or less refrangible sides of the rays lie in every direction, but as 

 soon as these sides are arranged, in the same direction by pris- 

 matic refraction or by diffraction, the light displays the same 

 properties as if it had originally formed part of a spectrum. 

 Some discussion among the members, on points connected with 

 this subject, ensued. 



Sir Wm. R. Hamilton then made a communication respecting 

 the propagation of light in vacuo ; and subsequently, on the 

 propagation of light in crystals. The object of these papers 

 was to advance the state of our knowledge respecting the law 

 which regulates the attractions or repulsions of the particles of 

 the ether on each other. 



Sir J. Herschel offered a Note on the Structure of the Vitreous 

 Humor of the Eye of a Shark. The result is, that the vitreous 

 humor, (so called,) of this fish is no jelly, but simply a clear li- 

 quid, inclosed in some close cellular structure of transparent 

 membranous bags, which, by their obstruction to the free move- 

 ments of the contained liquid, imitate the gelatinous state. 



Mr. Ball, of C. C. Cambridge, read a paper " O71 the weaning 

 of the Arithmetical Symbols for Zero and Unity .^ when used in 

 General Symbolical Algebra.'''' 



A communication was read from Prof. Forbes, " On Subterra- 

 nean Temperature ; and notice of a Brine Spring emitting Car- 

 bonic Acid Gas.''^ Observations had been made and were now 

 in progress, on the temperature of the earth at various distances 

 beneath the surface, in the vicinity of Edinburgh, the results of 

 which he intended to lay before the next meeting of the Associ- 

 ation. The brine spring is about a mile from Kissingen, Bava- 

 ria. It has 3 per cent of salt, and rises in a bore 325 Bavarian 

 feet deep in red sandstone ; but it is understood that the water 

 flows at about 200 feet in depth. Its temperature is never less 

 than 65°, — the mean temperature of springs near, being only 50° 

 to 52°. It discharges carbonic acid gas in volumes almost unex- 

 ampled, keeping the water, — in a shaft of eight feet diameter, — in 

 a state resembling turbulent ebullition. The enormous supply of 

 gas has led to its use in gas baths, for which purpose it is carried 

 off by a tube connected with a huge inverted funnel, which rests 

 upon the water. It contains scarcely a trace of nitrogen. It is 

 conducted into chambers properly prepared and thence into baths. 



