' 



THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



Aet. XLIY. — Radiation of Atmospheric Air; by C. O. 

 Hutchlnts, Bowdoin College. 



We learn from the researches of Tyndall that the radiation 

 from heated air streaming from about a copper ball heated to 

 near redness was just detectable, but scarcely measurable with 

 the most delicate apparatus then in existence. 



He was also able to show that other gases, under like condi- 

 tions radiated, some to a much greater extent than air, and he 

 formed a table in which the different gases experimented upon 

 stand in the order of their radiating powers. This at present 

 comprises about the sum of our knowledge of this important 

 matter. The recent invention of several forms of extremely 

 delicate heat-measuring apparatus now enables us to deal suc- 

 cessfully with quantities of heat so minute, that the ordinary 

 thermopile gives no indication of their existence. 



The apparatus used in the following investigation is some- 

 thing of an improvement upon that formerly here devised and 

 described* which improvement has been effected by the sub- 

 stitution of a junction of the bismuth, antimony and tin alloys 

 in place of the iron-nickel couple formerly employed. 



By a peculiar method of casting these alloys into thin leaves 

 it is possible to give them a certain amount of temper by 

 which their tenacity is considerably increased, so that by skill 

 and patience they can be worked into bars as small as 0*002 cm 

 thick, and 0*03 cm wide. More difficulty however being experi- 

 enced with the alloy of bismuth and antimony. To avoid too 



* Proc. Am. Acad., vol. xxiv. 

 Am. Jour. Sci.— Third Series, Vol. XLIII, No. 257.— May, 1892. 

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