22 SCIENCE IN SHOUT CHAPTERS. 



of which remove these difficulties. They were conducted 

 witli the assistance of Mr. Jonathan Wilkinson, the official 

 gas examiner to the Sheffield Corporation, using his photo- 

 metric and gas-measuring apparatus. We first determined 

 the'amount of light radiated by a single fish-tail gas-burner 

 consuming a measured quantity of gas per hour. We found 

 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 illumina- 

 tion, 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 afford- 

 ing 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 in- 

 tensely as the single flame. Other modifications of these 

 experiments, described in Chapter vii. of " The Fuel of 

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

 bon 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 

 sun may be produced by a photosphere having no greater 

 intrinsic brilliancy than the flame of a tallow candle, pro- 

 vided the flame is of sufficient depth or thickness. I see 

 good reasons for inferring that its intrinsic brilliancy is less 

 than that of a caudle somewhere between that and a 

 Bimsen's burner. 



A similar series of experiments upon the radiation of the 

 heat of flames through each other, indicated similar results; 

 but my apparatus for these experiments was not so delicate 

 and reliable as in the experiments on light, and, therefore, 

 I cannot so decidedly affirm the absolute diathermancy of 

 flame to its own radiations. Within the limits of error of 



