PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 649 



speculate on what possible chemical connection there may be between air 

 and water. The preponderance of these two substances on the purface of 

 our planet, and the probability that nitrogen is not the inert diluent in re- 

 spiration' that is generally supposed, might give rise to not irrational con- 

 jectures on some unknown bond between air and water. But it would be 

 rash to announce any theory on such a subject; better to test any guess 

 one may make by experiment, than to mislead by theory without sufficient 

 data, or to lessen the value of facts by connecting them with erroneoua 

 hypot'heses. 



Petroleum. 



At a meeting in London of gentlemen interested in the petroleum trade, 

 held on the 29th of March, the following resolutions, among others, were 

 passed : 



That tlie lowest poiiit of ignition of refined oil be lOO'' Fahrenheit. 



That the gravity of good mercliantable refined Pennsylvania petroleum 

 is not to exceed 812 at a temperature of 60^^ Fah., and that the gravity of 

 good merchantable crude Pennsylvania petroleum is not to exceed .820 at 

 the same temperature. 



The si)ecific gravity .812 mentioned in the above resolution corresponds 

 with 43 on the scale of Baume, tliat of .820 with 41. « 



Solar Spots. 



Sir John Herschel in an article in The Quarterly Journal of Science 

 throws out the suggestion, whether the original exciting cause of solar 

 spots may not be found in the circulation of an elliptic ring of planetary 

 matter, in a state of division sufficiently minute to elude telescopic vision, 

 having a major axis such as would correspond to an average period of 

 11 1-9 years, and an eccentricity such as would bring its perihelion within 

 the rcgit)n in question ; the matter of the ring being unequally distributed 

 over its circuit with a minimum and a maximum following in, by an inter- 

 val, somewhat less than its semi-circumference. By assuming certain con- 

 ditions as to the constitution of such a ring, and the extent of deviation 

 from an exact quantity in the periodic times of its component elements, he 

 finds that not only the shorter period of 11 1-9 years in the recurrence of 

 spots first determined, but also the longer one of 56 years insisted upon by 

 Br. Wolf and various other changes are susceptible of explanation. 



The Glacial Epoch. 



Dr. Frankland recently delivered a lecture before the Royal Institution, 

 of which the following are the leading points : 



1. The effects of the glacial epoch were felt over the entire globe. 

 2. This epoch occurred at a geologically recent period. 3. It was preceded 

 by a period of indefinite duration, in which glacial action was either alto- 

 gether wanting, or was at least comparatively insignificant. 4. During its 

 continuance atmospheric precipitation wa^ much greater, and the height of 

 the snow-line considerably less than at present. It was followed by a 

 period extending to the present time, when glacial action became again 

 insignificant. The sole cause of the phenomena of the glacial epoch was 

 the higher temperature of the ocean. Nature's apparatus for producing 



