MEASURING HE. 1 T FROM ST. 1 RS 445 



uring the distribution of energy in its spectrum. This is the dream of 

 the experimenter, and it is the goal toward which he has turned his 

 efforts. But, in order to accomplish useful results, the present investi- 

 gation shows that the radiation sensitivity must be still further in- 

 creased by a hundred-fold. In other words, the radiometric outfit 

 (including the reflecting mirror) must be sufficiently sensitive to detect 

 the radiation from a candle at a distance of more than 500 miles. The 

 instrument must be 10,000 times more sensitive than the one used by 

 Nichols fifteen years ago, and perhaps from 100,000 to 500,000 times 

 more sensitive than those used in the earliest attempts by Huggins and 

 others, almost half a century ago. This shows how insignificant has 

 been the gain in sensitivity in comparison with what will be required 

 in order to accomplish much on the radiation from stars. It will be a 

 nerve-racking investigation ; but it is not so appalling as the above 

 figures may indicate. Large reflectors are becoming more common 

 every year. However, a very large reflecting mirror may not be desir- 

 able. The gain in light-gathering power in a very large reflecting tele- 

 scope is not at all proportionate to the cost of manufacture and con- 

 venience of operation. The writer used a three-foot reflector, which, 

 although operated by hand, could be set very quickly. If a six-foot 

 reflector had been at his disposal the sensitivity would have been in- 

 creased by only four-fold. This shows how little is contributed by the 

 mirror, and how much of the burden as regards gain in sensitivity falls 

 upon the radiometer. 



The aforementioned extra hundred-fold gain in sensitivity required 

 may be attained by the use of a reflecting telescope having a mirror 

 seven feet in diameter, and by increasing the radiometer sensitivity 

 twenty times. If the sensitivity of the thermocouples used in the pres- 

 ent work can be increased two-fold, this will leave the galvanometer 

 sensitivity to be increased ten-fold. By using a special pier for the 

 galvanometer, and by using a light galvanometer suspension in a 

 vacuum, it will not be a very difficult task to increase the galvanometer 

 sensitivity ten- to twenty-fold. It looks, then, as though everything 

 were in our grasp — everything except a six- to seven-foot mirror, set 

 apart primarily for astroradiometric work. When one thinks of all 

 the money wasted in idle pleasure, and in the wars of nations, it is 

 pathetic to realize that but for a few hundred thousand dollars the 

 aforementioned "layman" of this generation might live to see some- 

 thing "practical" forthcoming from the investigation of the radiation 

 from stars. 



