Geology and Mineralogy. 87 



improvements in tubes or processes of regulation by patents. 

 Following the method adopted by Faraday, the author relates 

 both positive and negative results of his experiments. In the 

 subject of rarified gases, especially at low pressures, this method 

 in the present uncertainty of our knowledge is most useful ; for, 

 like the story of the Alpine climber who relates his attempts to 

 scale some most difficult aiguille, it stimulates the imagination 

 and leads to a consideration of all possible paths in the hope of 

 finding, even through failure, a way to the summit ; and in ulti- 

 mate success, the first path-breaker should not be forgotten. In 

 reading the list of contents of this volume one is surprised at the 

 richness of suggestion. Every form of X-ray tube, of regulators 

 and of exciters for such tubes, receives thought, and it is recog- 

 nized by those who have followed Dr. Rollins' work that the 

 present forms of the most enduring and most efficient tubes are 

 the result of his work. Makers of such tubes have eagerly taken 

 up his suggestions and by (we will charitably say) unconscious 

 cerebration have taken credit to themselves. This is true also of 

 the open construction of Ruhmkorf coils which the author fully 

 describes in his book, and the employment of a hinged Faraday ring 

 in the primary of such coils. This is a most efficient construction 

 of a transformer both for X-ray work, for spectrum analysis, and 

 for wireless telegraphy. No one in America appears to have had the 

 experience of Dr. Rollins in exhausting X-ray tubes to their point 

 of greatest efficienc}". He points out many phenomena of absorp- 

 tion and occlusion of gases by the various terminals he employed, 

 and. by the glass walls of the enclosure which are now being 

 studied quantitatively by various observers. This occlusion or 

 absorption can under certain conditions reduce the pressure in an 

 X-ray tube from one-thousandth of a millimeter to one two- 

 thousandth. The mechanical skill shown in the plates of appli- 

 ances for the employment of X-rays in surgery, which are collected 

 at the end of the volume, would suffice alone to make this a notable 

 work and a monument of altruism. j. t. 



II. Geology and Minekalogy. 



1. Indiana Geological Survey. — W. S. Blatchley, State 

 Geologist. 28th Annual Report, 1903, 553 pp., with plates, maps 

 and figures. — In addition to the statistical reports of the mine 

 inspector, the gas supervisor, etc., the Indiana Survey Report for 

 1903 contains articles by T. C. Hopkins and A. F. Foerste on the 

 Topography and Geological Formations of the state accompany- 

 ing the new Geological Map ; and a paper on the Stratigraphy 

 and Paleontology of the Niagara, by E. M. Kindle. There is also 

 a valuable table of contents of all of the geological literature 

 published by the state of Indiana. The report of the state gas 

 supervisor brings clearly to mind the great waste that has been 

 caused by the careless treatment of the natural gas supply. The 

 people of the state have finally been convinced that the gas sup- 



