150 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



emissive power and the different kinds of heat that certain 

 bodies emit at the temperature of boiling water. lie lias 

 established that for each substance there is a thickness at 

 which it has the greatest emissive ])ower ; second, that this 

 thickness varies from 3.45 millimeters for powdered rock-salt 

 to 0.03 for Indian-ink ; third, this thickness varies with the 

 consistency of the matter thus, for lamp-black directly de- 

 posited, it is 0.200 millimeter, while it does not exceed 0.0G9 

 when the lamp-black has been previously mixed with bisul- 

 phide of carbon ; fourth, as the same laws obtain in respect 

 to the absorbing powers of bodies, it follows that the therrno- 

 scopes, in order to produce their maximum effect, should be 

 covered with a shell equivalent to 0.2 millimeter of lamp- 

 black ; fifth, the different bodies present different emissive 

 power for different portions of the spectrum that is to say, 

 if the heat emitted by each at the temperature of boiling 

 water Avere visible, they would all appear of different colors 

 and of different intensities; sixth, no substance whatever 

 lias a maximum of transparency for those rays which it 

 emits at a temperature of 100 C. 



Dr. E. J. Mills, of Glasgow, contributes some notices of re- 

 sults of a minute inquiry into the constancy of the errors of 

 thermometers. The sets or secular change depend on the 

 temperature. The effects of external pressure and of the al- 

 ternate heatinsr and cooling were examined, and series of 

 standard bodies prepared, whose melting-points range from 

 35 to 121 (Fahr. ?), which can be used as tests for any new 

 thermometer. 



In reference to the idea of an instrument for registering 

 the sum total and the average temperature, several contribu- 

 tions have appeared, and among them one from William F. 

 Stanley [Nature, vol. xviii., p. 41), who describes an apparatus 

 invented by him in 18VG, and which is essentially a modifica- 

 tion of the pendulum clock, which seems to have considerable 

 merit. It should, however, not be forgotten that chronome- 

 ters have, for the past forty years, been frequently construct- 

 ed with large rates, for the purpose of ascertaining average 

 temperatures during longitude-campaigns. 



The recent publications of the Indian Meteorological Of- 

 fice at Calcutta, under Blanford, include, besides the " Ob- 

 servations," the "Memoirs," and the "Instructions" previ- 



