520 Scientific Intelligence. 



the negative. The results obtained for mercury were very con- 

 cordant and agreed with the mean value obtained by Quincke. 

 Strong electrification of the surface reduced the value of the 

 surface tension by more than 20 per cent. — Nature, April 17, 

 1890. j. t. 



7. Suppression of Photographic Halos. — MM. Paul Henry 

 and Prosper Henry state that these halos can be obviated by 

 covering the back of the negative with a film of collodion which 

 contains in solution a small quantity of chryso'idine. This var- 

 nish has an index of refraction which differs slightly from that of 

 glass. The halos from even the most brilliant stars are sup- 

 pressed completely by it. The varnish dries rapidly and is per- 

 fectly transparent. — Comptes Pendus, April 8, 1890/p. 751. 

 >. J. T. 



Ar 



II. Geology and Mineralogy. 



1. The Potomac or Younger Mesozoic Flora ; by Wm. M. 

 A Fontaine. Monographs of the U. S. Geological Survey, vol. xv, 



Washington, 1880. Text 377 pp. 4°. Atlas 180 plates, bound 

 separately. — This highly important and long looked-for work, 

 though bearing date 1889, did not appear until late in the spring 

 of the present year. Ever since the announcement of its general 

 nature and contents in the number of this Journal for August 

 1888 (vol. xxxvi, p. 119), anxious inquiries have been coming in 

 as to when it would be in the hands of scientific men. It is now 

 before the world and is all that its title indicates. As a revela- 

 tion of the hidden treasures of a little known deposit, placing the 

 appearance of the most prominent type of vegetation a long way 

 farther back in time than it had hitherto been recorded, it cannot 

 fail to awaken a lively interest among geologists and paleontolo- 

 gists, while as a monument of prolonged and patient labor in a 

 most difficult field of research, it reflects the highest credit upon 

 its author. It would be impossible to do justice in a brief notice 

 to a work of this nature. Suffice it to say that it is chiefly a 

 record of the facts, the important deductions that flow from these 

 being modestly left to the reader. Three hundred and sixty-five 

 species of fossil plants are described in the text and profusely 

 illustrated. The drawings, all by the author's own hand, were a 

 little too realistic for the process employed in their reproduction, 

 by which the perfection of the work suffers somewhat through no 

 fault of his. Professor Fontaine may almost be said to have 

 discovered this flora, and nearly every specimen was collected by 

 himself in the soft clays and preserved with the utmost difficulty. 

 Whatever may be the true age of this formation the fossil plants 

 must constitute the chief factor in determining it. l. f. w. 



2. Geological Survey of Missouri, Bulletin N~o. 1. — This first 

 Bulletin of the Survey contains after the Administrative Report 

 of the State Geologist, Arthur Winslow, an account of the Coal 

 beds of Lafayette Co., by Mr. Winslow ; of the Building Stones 

 and Clays, and Iron sands of St. Fran cois and Madison Cos., by 

 G. E. Ladd ; the Mineral waters of Saline Co., by A. E. Wood- 



