308 ANNUAL OP SCIENTIFIC DISCOVERY. 



Mr. Hopkins inquired into the evidence respecting the existence of an 

 atmosphere, or of water, on the moon. If any atmosphere existed, it must 

 be very rare in comparison with the terrestrial atmosphere, and inapprecia- 

 ble to the kind of observations by which it had been tested ; yet the ab- 

 sence of any refraction of the light of stars during occultation was a very 

 refined test. No equal means existed of ascertaining the presence of water 

 on the moon ; and if it did not now exist, the opinion of its former exist- 

 ence rested on very uncertain evidence. The large size of the lunar cra- 

 ters compared with any on the earth was accounted for if they were pro- 

 duced by the expansion of a fluid mass ; for there was no reason why 

 such a force should be materially less in the moon than the earth, whilst 

 gravitation was much less. The result would be, not only a much greater 

 elevation, but less tendency to fall. He considered the annular craters 

 "were the remains of dome-shaped elevations, of which the central part had 

 fallen in. The lunar craters were more numerous in proportion to the 

 terrestrial ; but there might have been many more on the earth which 

 have been w r ashed away. 



Mr. James Smith remarked that the perfection of the lunar volcanoes 

 might be due to atmospheric conditions, and referred to the great circular 

 crater of the Sandwich Islands as being terraced like Copernicus. 



Mr. Nasmyth expressed his very strong conviction of the total absence 

 of water, or of traces of watery action, on the moon, and also of the ab- 

 sence of any atmosphere. The sudden disappearance of stars behind the 

 moon, without any change or diminution of their brilliancy, was one of 

 the most beautiful phenomena that could be witnessed. 



ON THE ORIGIN OF COAL FIELDS. 



In a recent lecture before the Royal Institution, by Sir Chas. Lyell, on 

 the origin of coal fields, the lecturer stated that the force of the evidence 

 in favor of their identity in character with the deposits of modern deltas 

 has increased in proportion as they have been more closely studied. They 

 usually display a vast thickness of stratified mud and fine sand without 

 pebbles, and in them are seen countless stems, leaves, and roots of terres- 

 trial plants, free for the most part from all intermixture of marine remains, 

 circumstances which imply the persistency in the same region of a vast 

 body of fresh water. This water was also charged, like that of a great 

 river, with an inexhaustible supply of sediment, which, had usually been 

 transported over alluvial plains to a considerable distance from the higher 

 grounds, so that all coarser particles and gravel were left behind. On the 

 whole, the phenomena imply the drainage and denudation of a continent 

 or large island, having within it one or more ranges of mountains. The 

 partial intercalation of brackish water-beds at certain points is equally 

 consistent with the theory of a delta, the lower parts of which are always 

 exposed to be overflowed by the sea, even where no oscillations of level 

 are experienced. The purity of the coal itself, or the absence in it of 



