1884.] Energy and Radiation in Incandescence Lamps. 159 



FIG. l. 



reflect both beams on to a collimating lens L, whence they fall on a 

 dispersion apparatus, two spectra being formed on a screen, or in an 

 observing telescope. A slice of the two spectra is taken and com- 

 pared side by side by means of a " split " lens. The intensity of either 

 spectrum can be reduced by closing one of the slits, or by placing a 

 rotating disk of sectors between the slit and the screen, and adjusting 

 the opening of the sectors till equality of illumination is attained. 

 The above results were obtained by the latter mode of observation. 



Table III shows a ray selected from the spectrum whose intensity 

 was also compared with a ray of the same wave-length in the 

 spectrum of a gas flame. Tables IV, V, VI, and VII show the 

 readings made photometrically, through red and green glasses, of 

 different lamps, as compared with a candle-power, the observed and 

 calculated intensities being shown in juxtaposition. It will be seen 

 that the coincidences are very close, and seem to justify the con- 

 clusions we have drawn. Table VIII is an attempt to measure the 

 light as a whole from the incandescence lamp with that of sperm 

 candles. The results are as near as might be expected. 



Table II. 



