340 A. G. Mayer — Radiation and 



From these results, which confirm very closely those ob- 

 tained by an examination of the residues and recorded in our 

 former paper, it is evident that the concentration may go under 

 the most unfavorable conditions — when the maximum amount 

 of bromide is present — to 40 cm 3 without loss and to 35 cm 3 

 with small loss. As we stated in our former paper concentra- 

 tion below 35 cm 3 should be avoided. 



In our former paper we showed that the iodine could he de- 

 termined in unknown mixtures of sodium chloride, potassium 

 bromide, and potassium iodide taken in amounts not exceeding 

 1-5 grm. (in which, however, neither individual salt was present 

 in amount exceeding - 5 grm.) with a maximum error ranging 

 from 0*0013 grm. — to 0*001t> grm. + .. We showed, further, 

 that when the amounts of chloride and bromide present were 

 known also a correction for the action of these salts might be 

 applied which reduced the maximum errors to 0*0010 grm. — 

 and 0*0008 grm. +, and gave a mean error of 0*0001 grm. — 

 for twenty-six determinations. 



In conclusion we affirm the correctness of our former work 

 and reiterate our former directions without change. 



Akt. XL. — The Radiation and Absorption of Heat by 

 Leaves; by Alfred Goldsborough Mayer, M. E. 

 (Stevens Institute of Technology.) 



The present research was commenced in the Physical 

 Laboratory of the LTniversity of Kansas in the autumn of 1890, 

 and continued in the Jefferson Physical Laboratory of Harvard 

 University. 



As plants must necessarily receive a considerable portion of 

 their energy by the absorption of the sun's heat during the 

 daytime, and then lose some of this heat by radiation during 

 the night, it becomes of some interest to the physiological 

 botanist to determine what may be the laws of this periodical 

 sain and loss. Furthermore as by far the greater portion of 

 the land surface of the globe is covered by vegetation, the 

 laws of its radiation would become an important factor in a 

 determination of the radiation of heat by the earth. 



Apparatus. — In the research use was made of a highly sensi- 

 tive thermopile in connection with a low resistance, reflecting 

 astatic Thomson galvanometer. As it was feared that heating 

 the leaves to abnormal temperatures might alter the coefficients 

 of radiation of their surfaces, the form of apparatus shown 

 in fig. 1 was devised, by means of which the radiation from 

 leaves at the temperature of the air of the laboratory might 



