284 



LIGHT AND ITS ARTIFICIAL PRODUCTION. 



a similar manner to that in the lights just mentioned, by placing a 

 mantle of incombustible material in the very hot but nonluminous 

 Bunseu flame, thus bringing the mantle to incandescence. [Experi- 

 ment.] If the maximum luminosity is to be obtained, the incandescent 

 body must satisfy many theoretical conditions; especially, it must not 

 reduce the temperature of the products of combustion and must emit 

 as much light as possible corresponding to its temperature. Auer's 

 invention is not new in principle, and indeed had been anticipated in 

 practice. For instance, it is said that the streets of Nantes were illu- 

 minated by incandescent gaslights in which a mantle was brought to 

 incandescence in the hottest part of a Bunsen flame. The reason that 

 these lamps were so soon relegated to forgetfulness was entirely due to 

 the nature of the mantle, which was made of platinum wire instead of 

 the material Auer used. This example illustrates once more how the 

 very best principle can fail, and must fail if ignorantly and improperly 

 applied. In order to understand the superiority of the Auer light over 

 the ordinary gaslight and the related questions, why does one source of 



light emit more light than another, 

 and how does the increase of tem- 

 perature influence the intensity, we 

 must first familiarize ourselves with 

 two fundamental physical laws known 

 as Stefan's law of radiation and Kir- 

 choff's law of the absorption and 

 emission of light. Before doing this 

 however, I will briefly consider the 

 other sources of light commonly 

 employed. 



A new addition has recently been 

 made to the free-burning flames, 

 namely, the much-renowned and now 

 almost notorious acetylene light. 

 Director SchultzHencke was kind enough to place at my disposal for 

 this evening a generating apparatus which you see before you. [Experi- 

 ment.] Figure 2 shows its construction. It is built like an ordinary 

 gasometer, the outer vessel G G is iDartly filled with water, through 

 which the tube E R, provided with a cock /<, extends above the level of 

 the water. In the outer vessel is contained a second vessel P P, Avhich 

 carries suspended from the lid in the interior a basket K containing 

 about 200 grams of calcium carbide. The cylinder P P floating on the 

 water sinks by gravity as soon as the cock at H is opened, and the 

 inclosed air escapes through the tube E. But as soon as P P has sunk 

 so deep that the calcium carbide is brought into contact with the water, 

 acetylene gas is jiroduced, and a very explosive mixture of air and 

 acetylene gas escapes from the burner b. Nevertheless, I apply a 

 burning match to the burner. The gas is finally ignited and burns 



Fig. 2. 



