Geology and Natural History. 433 



sented by Du 2 /V. 2 The outstanding relative retardation is thus 

 only Du 2 /V 2 instead of the double of that quantity. Accepting this 

 correction we have to expect, according to Fresnel's views, a 

 shift of only "024 of a band in Michelson's experiment. Under 

 these circumstances Michelson's results can hardly be regarded as 

 weighing heavily in the scale. It is much to be wished that the 

 experiment should be repeated with such improvement as experi- 

 ence suggests. In observations spread over a year, the effects, if 

 any due to the earth's motion through space would be separated. 

 On the whole, Fresnel's hypothesis of a stationary ether appeal's 

 at the present time the more probable, but the question must be 

 considered to be an open one." — Nature, March 24, 1892. j. t. 



11. Nirchhoff' 's Law arid the radiation of Gases. — Kirchhoff's 

 law is the theoretical fundamental law for the spectrum analysis 

 of stars. It states that bodies emitting light absorb light of that 

 wave length for which their emission spectrum shows a maximum. 

 E. Pringsheim draws attention in an exhaustive article to the 

 fact that the spectra of gases are generally studied by means of 

 electrical discharges in Geissler tubes and that we have no direct 

 evidence that mere increase in temperature suffices to make a gas 

 glow. W. Siemens says in regard to this point : " To my knowl- 

 edge investigations upon the question whether pure gases raised 

 to a high temperature emit light rays have not been made." 

 Siemens has shown that oxygen, carbonic acid, nitrogen and 

 hydrogen, do not emit light rays even when heated to 1500° C. 



Pringsheim therefore sets himself to determine : 



1. Have gases the power to emit light merely from high temper- 

 ature. 



2. Can we form gaseous sources of light, which satisfy the 

 conditions of Kirchhoff's law. 



The conclusions he arrives at after much experimental work 

 are the following : 



1. There is no gaseous source of light which satisfies Kirchhoff's 

 law. 



2. Glowing gases, the temperature of which is below 150° C. 

 can be obtained (cold flames). 



3. The salts of sodium glow in flames only by means of chem- 

 ical processes (reduction). 



4. Metallic sodium heated in neutral gases, glows only from a 

 chemical process. 



5. The hypothesis that gas merely through rise in temperature 

 can be made luminous, can be supported neither experimentally 

 or theoretically. — Ann. der Physik und Chemie, No. 3, 1892, pp. 

 428-459. j. t. 



II. Geology and Natural History. 



1. Note on the distribution of the upturned Cretaceous beds 

 of British America, by Dr. George M. Dawson. (Editorial 

 Correspondence.) — To the north of the International Boundary 



