250 American Associatimi. 



the difference between the rapidity of combustion in the 

 light and in darkness being extremely small, and sometimes 

 in favor of the light and sometimes in favor of the darJ-, 

 while the difference between them on different days sometimes 

 amounted to 9 per cent. This fact he. held to be a proo. 

 that the former theory had been too rashly generalised from 

 isolated facts, and he came in general to the conclusion that the 

 observed influences upon the rate of combustion were due to 

 the state of the atmosphere, and not to any Solar action. Follow- 

 ing up this conclusion, and guided by a large number of well 

 authenticated and carefully observed experiments carried on under 

 various circumstances, the deduction drawn was that combustion 

 was retarded by rarifiaction and accelerated by condensation. He 

 then detailed a number of observations by which it was found that 

 the ratio of combustion was greater than the ratio of density. 

 One great result of all these observations and experiments was that 

 there is an immense number of atmospheric influences, the effect 

 of which have as yet been undiscovered. There were, however, 

 two conclusions which he believed to be established. First, that 

 Solar light does not seem to exercise any sensible effect upon 

 combustion ; and secondly, that variations in the density of the 

 air do exert a striking effect in retarding or accelerating the rapi- 

 dity of the process — the rate of burning augmenting with every 

 increment of density, and vice versaP 



Prof. Olmstead of Yale College, communicated an interest- 

 ing paper on 



TPIE AURORA BOREALIS, 



ia which he criticised the Electric theories of this phenomenon : 

 — " The Professor commenced by a reference to a paper which 

 he had previously written on this subject, and which was 

 published among the contributions to the Smithsonian Insti- 

 tute. In this paper he had recorded a number of facts 

 derived from a series of observations upon the very strick- 

 ingly magnificent Auroras which had been witnessed during 

 a period of about twenty years, commencing about the year 1837. 

 The theory which he had deduced from these facts was, that 

 contrary to the general hypothesis which ascribes the Aurora to 

 Terrestrial sources, its origin was cosmical, the matter being de- 

 rived from the planetary spaces. — His arguments in favor of this 

 theory, in opposition to the electrical hypothesis, were based upon 

 the immense extent of the phenomena beyond the reach of atmc? 



