Prof. Tyndall on Calorescence. 389 



lowing Table contains a series of measurements executed in this 

 manner. The motion of the pile is measured by turns of its 

 handle, every turn corresponding to the shifting of the face of 

 the instrument through a space of one millimetre, or ^th of an 

 inch. At the beginning, where the increment of heat was slow 

 and gradual, the readings were taken at every two turns of the 

 handle ; on quitting the red, where the heat suddenly increases, 

 the intervals were only half a turn, while near the maximum, 

 where the changes were most sudden, the intervals were reduced 

 to a quarter of a turn, which corresponded to a translation of 

 the pile through yoo tn °^ an mcn - Intervals of one and of two 

 turns were afterwards resumed until the heating-power ceased 

 to be distinct. At every halting-place the deflection of the 

 needle was noted, the value of the deflection, referred to the first 

 degree as unit, being placed in the first column of figures in the 

 Table. It was found convenient to call the maximum effect in 

 each series of experiments 100 ; the second column of figures, 

 obtained by multiplying the first by the constant factor 1*37, 

 expresses the heat of all the parts of the spectrum with refer- 

 ence to this maximum. 



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



V 1 nf Calorific intensity, 



Movement of pile. deflection in 100ths of the 



maximum. 



Before starting (pile in the blue) 0*0 0*0 



Two turns forward (green entered) 1*5 2*0 



3-5 4-8 



5-5 75 



„ (red entered) 15\5 21-0 



„ (extreme red) 32*6 44-6 



Half turn forward 44-0 600 



54-0 74 



62-0 85 



700 95-8 



72-5 99 



Quarter turn forward, maximum . 73*0 100*0 



70-8 97-0 



Half turn forward 57-0 78-0 



45-5 620 



32-6 44-5 



260 356 



Two turns forward 10'5 14*4 



65 9 



„ 50 6-8 



„ 3-5 5 



2-5 34 



1-7 2-3 



1-8 1'8 



Phil Mag. S. 4. Vol. 31. No. 210. May 1866. 2 D 



