SMITHSONIAN EXPLORATIONS, I928 3 



fineness of its suspending fiber may be gathered from the fact that a 

 fragment of a Dennison gummed label, ^ inch wide and | inch long, 

 was too heavy to be carried without breakage by the quartz fiber. 

 Also it was found that when suspended in a wide bottle in air at 

 ordinary atmospheric pressure the top of the suspending fiber could 

 be turned through more than 40 complete turns before the little 

 radiometer hung at its lower end responded by any perceptible rota- 



700O 9050 Iil60 17510 22240 ANCSTR6m5 



Fig. 2. — Distribution of heat in the prismatic spectra of i8 stars and 2 planets. 



tion. The air, in fact, acted as if viscous, like molasses, to this 

 minute force. 



In order to observe the indications of the radiometer, it was pro- 

 vided with a mirror made by thinly ])lating with i)latininn a bit of 

 glass smaller than the head of a pin, and made l)y grinding and polish- 

 ing to one-third ordinary thickness the cover glass used for mounting 

 specimens for microscopic examination. This thin mirror reflected a 

 little auxiliary beam of electric light to a distance of almost 20 feet. At 

 the hottest parts of their spectra most of the stars examined, though 

 their rays were collected by the great 100-inch telescope, were only 

 powerful enough in shining on the fly-wing vane of the instrument 



