PROFESSOR TYNDALL ON CALORESCENCE. 5 



between the two observations. The following Table contains the record of a series 



of such measurements. As in the last case, the motion of the pile is measured by turns 



of the handle, and the values of the deflections are given with reference to a maximum 



of 100. 



Table II. — Distribution of Heat in Spectrum of Electric Light. 



,,,«., Calorific intensity, in lOOths 



Movement of pue. „ , , ? ' 



*^ of the maximum. 



Maximum 100 



One turn towards visible spectrum 94*4 



» 65-5 



42-6 



55 5> 



55 55 



55 55 



55 55 



55 55 



(extreme red) 2 8' 3 



20-0 



14-8 



Ill 



Two turns in the same direction (green entered) 7*4 



4-6 



2-0 



(pUe in blue) 0-9 



55 55 



S> 55 



Pile brought back to maximum. 



Maximum 100*0 



One tViicTx from visible spectrum 67 "1 



41-0 



23-0 



13-0 



55 55 ..... 9*4 



Two turns 50 



3-4 



0-0 



More than a dozen series of such measurements were executed, each series giving 

 its own curve. On superposing the different curves, however, a very close agreement 

 was found to exist between them. The annexed curve (fig. 3), which is the mean of 

 several, expresses, with a close approximation to accuracy, the distribution of heat in 

 the spectrum of the electric light from fifty cells of Grove. The space A B C D repre- 

 sents the invisible, while CDE represents the visible radiation. We here see the 

 gradual augmentation of thermal power, from the blue end of the spectrum to the red. 

 But in the region of dark rays beyond the red the curve shoots suddenly upwards in 

 a steep and massive peak, which quite dwarfs by its magnitude the portion of the dia- 

 gram representing the visible radiation*. 



* How are we to picture the vibrating atoms which produce the different wave-lengths of the spectrum ? 



