COBLENTZ: MODIFICATIONS OF THERMOPILES 513 



more dependent upon nicety of construction than upon the use 

 of materials having a high thermoelectric power. 



The construction and tests of a radiometer attachment for 

 monochromatic illuminators is given. This device consists of 

 a linear thermopile, which moves in vertical ways in front of the 

 exit slit of a spectroscope. It is useful in measui-ing the energy 

 value (mechanical equivalent) comprised in the different wave 

 lengths of light used as stimuli, in biological, chemical, physical, 

 and physiological investigations. 



The method of construction, and tests are given of a thermopile 

 to be used for absolute measurements of radiation. The device 

 consists of a linear thermopile of bismuth and silver, with a 

 continuous receiving surface, in front of which is situated a 

 strip of manganin or platinum, which is blackened electrolyti- 

 cally with platinum black. This strip of metal is exposed to 

 radiation and in turn radiates to the thermopile which causes a 

 galvanometer deflection. The strip of metal is then heated 

 electrically to cause a similar deflection of the galvanometer 

 needle; and the power expended gives a measure of the radiation 

 in absolute value. The instrument gives a value of the coefficient 

 of total radiation of a black body which is in excellent agreement 

 with values obtained by other methods. 



Among the group of special designs, the stellar thermoele- 

 ments m.ay be mentioned. When used with a reflecting muTor, 

 92 cm. (26 inches) in diameter, and an ironclad Thomson gal- 

 vanometer of ordinary sensitivity, it was possible to make quanti- 

 tative measurements of the total radiation from stars -down to 

 the 5.3 magnitude, while high qualitative measurements were 

 made on stars down to the 7th magnitude. The application 

 of the thermoelement to solve astronomical problems appears 

 therefore to be feasible. 



The design and tests are given of an absolute thermopile for the 

 measurement of nocturnal radiation; also of a thermopile to be 

 used as a photometer to measure the blackness of star images 

 on photographic plates. A novel design for a special biological 

 problem consisted in the construction and testing of a hnear 

 thermopile, in which the receiver was bent into a U-shaped 



