1871-] The Fuel of the Sun. 447 



But ere this, a great difficulty has probably presented itself 

 to the mind of the reader. He will refer to the calcula- 

 tions that have been made in order to determine the actual 

 temperature of the solar surface and the intensity of its 

 luminosity. Both of these are vastly in excess of those 

 obtained in our laboratory experiments by the com- 

 bustion of the elements of water. Even taking into consi- 

 deration the dissociated carbonic acid whose elements 

 should be burning in the photosphere with those of water, 

 and adding to these the volatile metals of the solar nucleus 

 whose dissociated vapours must, under the circumstances 

 stated, be commingled with those of the solar atmosphere, and 

 therefore contribute to the luminosity by their combustion, 

 still by burning here on the earth a jet of such mixed gases 

 and vapours we should not obtain any approach to either 

 the luminosity or the temperature which is usually attri- 

 buted to the sun. 



I have made a few very simple experiments, the results of 

 which I think remove entirely these difficulties. They were 

 made with the assistance of Mr. Jonathan Wilkinson, the 

 official gas examiner to the Sheffield Corporation, using his 

 photometric and gas measuring apparatus. We first de- 

 termined the amount of light radiated by a single fish-tail 

 gas-burner consuming a measured quantity of gas per hour. 

 We found that when another was placed behind this, so 

 that all the light of the second had to pass through the 

 first, that the light of the two (measured by the illuminating 

 intensity of their radiations upon a screen just as the solar 

 luminosity has been measured) was just double that of one 

 flame, three flames (still presenting to the photometric 

 screen only the surface of one) gave it three times the 

 amount of illumination, and so on with any number of 

 flames we were able to test. Mr. Wilkinson has since 

 arranged 100 flames on the same principle, i.e., so that the 99 

 hinder flames shall all radiate through the one presented to 

 the screen, thus affording the same surface as a single flame, 

 but having 100 times its thickness or depth, and he finds that 

 the law indicated by our first experiments is fully verified ; 

 that the 100 flames thus arranged illuminate the screen 100 

 times as intensely as the single flame. Other modifications 

 of these experiments described in chapter 7 of " The Fuel of 

 the Sun," establish the principle that a common hydro- 

 carbon gas flame is transparent to its own radiations, or in 

 other words, that the amount of light radiated from such a 

 flame, and its apparent intensity of luminosity, is pro- 

 portionate to its thickness ; therefore the luminosity of the 



