of Heat in the Visible Spectrum. 



205 



difference of wave-length of 100 was taken as the unit, and 

 the difference between the values of the ordinates divided by 

 100 considered as a measure of the dispersion. The ordinates 



of the heat-curve of MM. Fizeau and Foucault at eighteen 

 points in the spectrum, midway between those at which the 

 ordinates of the dispersion-curve had been taken, were mea- 

 sured in tenths of an inch, these numbers divided by those 

 representing the dispersive power of the prism, and the quo- 

 tients taken as giving the true relative intensity of the heat at 

 the different points of the spectrum. 



