F. J. Rogers— Magnesium as a Source of Light. 301 



points where they disappear on its eastern and northern 

 borders. 



Differential uplift was slight in the western Erie basin com- 

 pared with what it was in the eastern Erie basin and the On- 

 tario, in Michigan, and on the Canadian shores of Lake Huron 

 and Georgian Bay. The data at hand indicate that it amounts 

 to scarcely more than ten feet in the whole area of the portion 

 of the Erie basin west of Cleveland, and has therefore played 

 an insignificant part in causing the three stages of the lake 

 herein described. 



The bulk of the moraines is many times that of the beach 

 deposits, though no longer time was involved in their deposi- 

 tion. The ice-sheet was therefore a much more efficient trans- 

 porting agency than the lake waves. 



The extreme scarcity of evidence of life in these waters, 

 though negative in its nature, and therefore to be taken with 

 caution, is quite accordant with the theory deduced from the 

 relation of the beaches to the moraines, viz : that the beaches 

 are of glacial age. 



Art. X.X.XV I.— Magnesium as a Source of Light ; by 

 Frederick J. Kogers, M.S. 



[Contributions from the Physical Laboratory of Cornell University, No. 9]. 



I. 

 Quality of Magnesium Light. 



The light produced by the combustion of magnesium is 

 brilliantly white. It is whiter than the arc light and almost 

 rivals sunlight itself. When the spectrum of the magnesium 

 light is formed side by side with that of ordinary gaslight, the 

 former is immediately seen to be relatively much stronger in 

 the more refrangible rays. It gives a continuous spectrum, 

 superimposed upon which are the ever present sodium lines 

 Dj D 2 and the magnesium lines h 1 b 2 & 4 as well as four or five 

 oxide bands. 



In the experiments to be described in the first part of this 

 paper the brightness of magnesium light in different parts of 

 its spectrum was compared with the corresponding components 

 of gaslight from an Argand burner by means of the " hori- 

 zontal slit " photometer.* This is a spectrophotometer mov- 

 able along a, photometer bar. It furnishes, side by side, 

 spectra of the two sources of light to be compared, the two 



* Described by Dr. E. L. Nichols, in Trans. Am. Inst, of E. E., vol. vii. 



