34 J. W. Draper—New form of Spectrometer. 
were, condenses the colored spaces more and more as we pass _ 
toward the red, increasing the intensity of the light as it does 
that of the heat. 
n the grating, or diffraction spectrum, the luminous 4 
intensity is equal in all the visible regions, all the colors being — 
simultaneously obliterated by an extinguishing light. 
t must, however, be borne in mind that these conclusions 
should be taken in eonnection with the physiological action of 
the eye. Owing in part to the imperfect transparency of its 
media, and partly to the inability of its nervous mechanism _ 
to transmit waves of certain frequency to the brain, the spec- __ 
trum does not begin and end sharply, as to a perfect eye a 
perfect spectrum ought to do. 
There are, hence, two causes which must not be overlooked _ 
in these observations. 1st. The physiological peculiarity of © 
the eye, which gives to each end of the spectrum the aspect of 
gradually fading away. 2d. In the case of solar-light the 
absorptive action of the atmosphere, which is chiefly exert 
on the more refrangible rays. 
think, bearing in mind the correlation of light and heat, © 
both being corresponding manifestations of the same vibratory — 
movement in the ether, that these results substantiate those 1 . 
published in 1872, on the distribution of heat in the spectrum; 
and that as the different colored spaces are equally luminous, 
so they are equally warm 
I have sabi 
€ some attempts to compare with each other the — 
Juminous intensity of the bright lines in various spectra, espe- 
cially those emitted by a strontium flame, but not being able to — 
1 hes at present, I have postponed them to — 
continue these researe 
a more favorable opportunity. 
University of New York, May 5th, 1879. 
a ad 
a 
