22 



THE POPULAR SCIENCE MONTHLY. 



of the tasimeter, what was previously only a matter of conjecture was 

 proved to be a certainty that the corona of the sun emits heat. The 

 apparatus above described was arranged with as much care as pos- 

 sible, so that the smallest amount of heat might be detected. So great 

 was the delicacy of the instrument that, at the time of total eclipse, 

 when the beam from the corona was allowed to fall upon the tasimeter, 

 the spot of light reflected from the galvanometer mirror not only 

 changed its position, but moved completely off the scale which had 

 been provided ; so that, while the presence of heat in the corona was 

 demonstrated, measurement of it was impossible. The instrument has 

 also been used in measuring the beat of some of the stars. 



Fig. 7. 



Besides being used as a delicate thermometer, the tasimeter also 

 serves as a means of determining the coefficient of expansion of bodies ; 

 for, by having a micrometer screw attachment, the amount of expan- 

 sion can be readily determined. By turning the screw, when the 

 needle has been deflected, until it is brought back to zero, the increase 

 in length can be read by the number of turns or parts of a turn the 

 screw has been moved. Fig. 8 gives a section of the tasimeter, 

 showing the micrometer screw. The piece of material to be tested is 

 seen at A, being clamped rigidly at B, and resting in a metal socket M, 

 which rests upon the carbon placed in the battery circuit as indicated. 



