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MEASURES FEEBLE HEAT STARS SEND TO 

 EARTH 



By measuring a hundred millionth degree of 

 temperature and a trillionth of an ampere of elec- 

 tric current. Dr. C. G. Abbot, of the Smitisonian 

 Institution, has determined for the first time the 

 heat spectrum of starlight with great accuracy. 



Working with the lOO-inch telescope at Mt. 

 Wilson Observatory this fall, Dr. Abbot measured 

 the heat at different parts of the spectrum of ten 

 stars and the sun. The rays were dispersed by a 

 spectroscope in a band similar to the rainbow. 



The bright star Capella, which is veiy similar 

 to our own sun in its spectrum, was found to fur- 

 nisli the equivalent of one horse power to an area 

 on the eartli approximately equal to the state of 

 Minnesota. But this prominent star is feeble 

 compared mth our sun, which is equal to a hun- 

 dred billion Capellas and sends down on twenty 

 square feet heat equal to a horse power. On the 

 whole earth Capella 's heat equals 500 horse power, 

 and as aU the stai-s together equal 500 Capellas 

 this would amount to 250,000 horse power over 

 the whole earth from the stars alone. 



Dr. Abbot explained that his work on the heat 

 of stars, accomplished with the cooperation of 

 L. B. Aldrieh of his staff, is an outgrowth of the 

 principal work of the Astrophysieal Observatory, 

 which is the investigation of the sun. 



' ' This work was begun about 1890 by Dr. S. P. 

 Langley whose great pioneer work in measuring 

 the sun's heat, its distiibutdon ,in the spectrum, 

 and the losses and modifications which it encoun- 

 ters in passing through the earth's atmosphere, 

 were classic," said Dr. Abbot. 



"It might be supposed that the investigation 

 of a heat source whose in-put on the earth's sur- 

 face amounts to the equivalent of a horse power 

 per couple of squaa-e yards would require only 

 simple and insensitive apparatus, but such is not 

 the case. The complexity of the solar beam, made 

 up of rays of greatly differing wave length which 

 are all differently transmitted by the earth's 

 atmosphere, requires the employment of the spec- 

 troscope to separate the rays, and for the recog- 

 nition of their heat the use of highly sensitive 

 thermometric apparatus. 



' ' The most satisfactory heat instrument f or 

 these purposes is the bolometer, invented by Lang- 

 ley about 1880. Two hair-like wires of platinum 

 are placed side by side, the one hidden from the 

 rays by means of a metaUie diaphragm, the otier 

 exposed in the spectrum. The heat aibsorbed by 

 the exposed thread, if it be as little as the niil- 

 Eonth of a degToe, suffices to disturb a sensitive 

 electrical balance, and by a beautiful device intro- 

 duced by Langley in the earliest years at the 

 Astrophysieal Observatory these indications are 



