SCIENCE. 



Editorial Committee : S. Newcomb, Mathematics ; K. S. Woodwakp, Mechanics ; E. C. Pickekixo, As- 

 tronomy ; T. C. JlEXDEXHALL, Physics ; K. H. Thuestox, Enffineering ; Ira Remsex, Chemistry ; 

 J. Le Coxte, Geology; W. M. Davis, Physiograpliy ; O. C. Marsh, Paleontology; W. K. Bbooks, 

 Invertebrate Zocllogy ; C. Hakt JIerkiam, Vertebrate Zoology ; S. H. ScfimER, Entomology ; 

 N. L. Britton, Botany ; Hexry F. Osborn', General Biology ; H. P. Bowditch, 

 Physiology ; J. S. Billings, Hygiene ; J. McKeex Cattell, Psychology ; 

 Daxiel G. Beixtox, J. W. Powell, Anthropology. 



Friday, June 28, 1895. 



CONTENTS: 



Argon : LORD Rayleigh 701 



Lloyd Morgan Upon InsfincI : H. F. O ~V2 



Some Uleamhring Hirers of Witconsin : Hexky B. 

 Kummel 714 



Correspondence : — 716 



Mitsoiiri Botanical Garden : Wm. Trelease. 



Scientific Literature : — 717 



TTie Geology of the Sierra Nevada : Ani>eew C. 

 Lawsox. Allen on the Genus Seithrodontomys : 

 C. H. M. 



Notes and Xetcs : — - 721 



Tlie Remedy for Pear Blight : M. B. Waite. i\>ic 

 York Botanic Garden ; Tlie Helmholtz Memorial ; 

 General. 



Societies and Academies : — 725 



Biological Society of Washington ; Entomological 

 Society of Washington ; The New York Academy 

 of Science ; Tlie Wisconsin Academy of Sciences, 

 Arts and Letters ; The Texas Academy of Science. 



New Books 728 



MSS. intended for publication and books, etc., Intended 

 for review should be sent to the responsible editor. Prof. J. 

 McKeen Cattell, Garrison on Hudson. N. Y. 



Subscriptions and advertisements should be sent to Scienxe, 

 41 X. Queen St., Lancoster, Pa., or 41 East 49th St., New York. 



AKGON.* 

 It is some three or four years since I hail 

 the honour of lecturing here one Friday 

 evening upon the densities of oxygen and 

 hydrogen gases, and upon the conchisions 

 that might be drawn from the result.s. It 

 is not necessary, therefore, that I sliould 



*A Lecture given by Lord Rayleigh before the 

 Royal Institution of Great Britain, on Friday, April 

 ."i, 1895. Reprinted from the official' report. 



trouble you to-night with any detail as to 

 the method bj- which gases can be accur- 

 ately weighed. I must take that as known, 

 merelj- mentioning that it is substantially 

 the same as is used by all investigatore 

 nowadays, and introduced more than fifty 

 years ago by Regnault. It was not until 

 after that lecture that I turned my atten- 

 tion to nitrogen ; and in the first instance 

 I employed a method of preparing the gas 

 which originated with Mr. Vernon Har- 

 court, of Oxford. In this method the oxy- 

 gen of ordinary atmospheric air is got rid 

 of with the aid of ammonia. Air is bubbled 

 through li(iuid ammonia, and then passed 

 through a red-hot tube. In its passage the 

 oxygen of the air combines with the hj'dro- 

 gen of the ammonia, all the oxygen being 

 in that way burnt up and converted into 

 water. The excess of ammonia is subse- 

 quently absorbed with acid, and the water 

 by ordinary desiccating agents. That method 

 is very convenient ; and, when I had ob- 

 tained a few concordant results by means 

 of it, I thought that the work was complete, 

 and that the weight of niti'ogen was satis- 

 foctorily determined. But then I refiected 

 that it is always advisable to employ more 

 than one method, and that the method that 

 I had used — Jlr. Vernon Harcourt's method 

 — was not that which had been used by any 

 of those who liad preceded me in weighing 

 nitrogen. The usual method consists in 

 absorbing the oxygen of air by means of 



