394 Hutchins — Radiant Energy of Standard Candle. 



We now have the whole radiant energy of the candle — 



47rxTob 2 X 75X17 



e = — , nnn = 1*23 X 10 ergs per second. 



1-303 & F 



To find what portion of this total energy lies in the visible 

 spectrum could be satisfactorily accomplished only by meas- 

 ures made in every part of the spectrum of the candle. Such 

 measures have been made by Langley* in the spectrum of an 

 argand gas-lamp with a glass chimney. He finds 24 per cent 

 of the total radiant energy to be visible. It is easy to compare 

 the candle with such a lamp. At a certain distance from the 

 thermograph an argand lamp, whose light was that of ten 

 candles, gave a deflection of 238 scale divisions. When the 

 lamp was replaced by the candle the deflection was 29. 

 Hence we see that very nearly 2 per cent of the radiant energy 

 of the candle is visible ; or the visible part is 246 X 10 6 ergs 

 per second ; about 10'9 ft. lbs. per minute. 



We may now proceed to find the mass of a meteor, first 

 upon the supposition that its rays have the same ratio of 

 visible to total energy as do those of the candle, and later, 

 correct, if possible, the value thus found. 



Let the meteor at a distance of 50 miles have a light equal 

 to that of Yega ; let it continue for 2 seconds with a velocity 

 of 25 miles per second. From the best data we find that, if 

 the meteor were at 1 meter distance the log of its candle power 

 would be 3*9851. Hence to find the energy e, we have : 



log candle power 3*9851 



log energy of candle 8*0899 



log 2 0*3010 



log s 12*3760 



2e 

 We have for the mass, m = — 7, and employing the data as- 

 sumed above we find m = 0*2936 gm. 



If the meteor in burning produce, for a given expenditure 

 of energy, more light than does the candle, then a less mass 

 than the one found would serve to produce the light given by 

 the meteor. From what has been observed of the spectra of 

 meteors, it is safe to conclude that their light is mainly due to 

 incandescent vapors of the materials composing the meteors. 

 It is also known that the spectra of these substances remain 

 unchanged throughout very considerable changes of tempera- 

 ture, and we may therefore be permitted to draw conclusions 

 from laboratory experiments upon these substances in the state 

 of vapor. 



* Science, vol. i, p. 482. 



