Mabch 2, 1883.] 



SCIENCE. 



89 



pressed the opinion that such a system would 

 be highly desirable. 



Then followed a long discussion upon the 

 standard of light. It was generally granted 

 that a white light was desirable. Wiedemann 

 remarked, that a fine gauze saturated with the 

 spirit of turpentine, burning in os^-gen, gave 

 a very white light. Siemens proposed to em- 

 ploy a current of oxygen passing through a 

 carburetted hj'drogen, maintained at some 

 fixed temperature. One could thus obtain a 

 constant mixture which would burn with a 

 white flame. Helmholtz thought that it would 

 be extremely difficult to produce a mixture 

 of air and carburetted hydrogen in constant 

 proportion, and to regulate the temperature. 

 Dumas thought- that the late experiments of 

 VioUe upon the light emitted by melting plati- 

 num might solve the problem. The point of 

 fusion of a body seemed to him to be as good a 

 fixed point as could be wished. He invited the 

 commission to view the experiments of Violle. 

 , After witnessing the experiments of Violle, 

 the members of the commission appeared to 

 think more favorably of Dumas' suggestion. 

 Professor Leblanc, who has had charge for 

 many j^ears of the photometric determinations 

 of the lighting-gas of Paris, was invited to 

 explain his methods ; and the members of the 

 commission, in turn, were invited to witness 

 the methods in his laboratory. Professor Le- 

 blanc stated his preferences for the employment 

 of a Carcel lamp for photometric determina- 

 tions. He showed that the personal equation 

 could be practically eliminated, and that dif- 

 ferences of tint did not influence the results to 

 the degree supposed. Sir W. Thomson spoke 

 of the advantages of Rumford's photometer. 

 The following resolutions upon this subject 

 were finally adopted : — 



a. The conference express their hope that 

 the experiments now in process upon the light 

 emitted bj' melting platinum will lead to a 

 definite standard of light. 



6. The}- recommend the emploj'ment of the 

 Carcel lamp as a secondary- standard, this lamp 

 to be employed with the precautions adopted 

 by MM. Dumas and Regnault. 



Candles can also be emploj'ed as a second- 

 ary standard, if sufficient care be taken in 

 regard to their construction and constitution. 



c. They call attention also to the necessity 

 of the analysis of the different conditions under 

 which comparisons of light are made, and re- 

 iterate the opinions, expressed at the meeting 

 of the electrical congress of 1881, in regard 

 to the necessity of taking into account the 

 amount of light radiated from sources of light 

 in different directions. 



At the close of the conference. Sir W. Thom- 

 son expressed the opinion that the labors of 

 the conference would stimulate researches dur- 

 ing the coming j'ear ; and he congratulated the 

 conference upon its important work. 



On the 26th of October, President Gr6vy 

 received the members of the commission at 

 the Palais d'Elysees ; and, after a reception by 

 Minister Coch^ry, on the afternoon of the same 

 day, the conference was adjourned to the first 

 Monday of October, 1883. 



ON THE PHYSICAL CONDITIONS UNDER 

 WHICH COAL WAS FORMED.'^ 



The mode of formation of coal has been 

 much discussed, and various theories have 

 been promulgated in regard to it ; but the 

 peat-bog theory, as it is called, has been 

 generally accepted. This is the view, that coal 

 is the residual hydrocarbon of plants which 

 have grown where their remains are found, 

 and that it has been formed precisely as peat 

 accumulates in marshes at the present day. 



So great has been the harmonj' of opinion 

 on this subject, that it would at first sight 

 appear unnecessary to renew discussion on a 

 question that, had seemed to be definitely and 

 permanently settled. The calm of geological 

 opinion which has prevailed on the coal-ques- 

 tion has, however, been recently disturbed by 

 a verj' voluminous and painstaking discussion 

 of the mode of formation of coal, hy M. 

 Grand'Eurj', which occupies nearlj- 300 pages 

 in the Annales des mines for the present year. 

 In this discussion the theory is advocated, that 

 the carbonaceous matter forming beds of coal 

 has been derived from plants, but plants trans- 

 ported from their places of growth, and de- 

 posited at a greater or less distance in the 

 bottom of water basins. 



1 Kead before the National academy of science^ at its semi- 

 annual meeting in New York, Nov. 14-17, 1S82. 



