On the Refraction of Light. 355 
able distance from the prism, which, considering the divergent pow- 
er of the lens beyond its focus, should be much nearer than is re- 
isite for examining the common spectrum. ‘The prism employed 
is very liable to be broken, from the quantity of heat concentrated 
on it by the lens. ; 
The luminous pyramids before spoken of are probably images of 
the prism, which pass in minature through the foramina in the leaden 
plate, and augment in magnitude as their distance from the lead’ in- 
creases ; for when, instead of using the homogeneous rays issuing 
from a prism, we place red or blue glass in the aperture through 
which the solar beam is admitted, and allow the rays to pass through 
holes in a plate of lead ; on receiving the images on. paper at some 
distance from the metal, we shall find them to be perfectly circular. 
It has been maintained by a few of those who have written on the 
inflection. of light, that some of the calorific rays are more diffrangi- 
¢ than others, and as a corollary to this, it follows that differently 
Colored rays, after passing through punctures of equal diameters will 
m figures whose bases, if received on a white surface, will appear 
_ of different sizes. T’o ascertain the truth of this position, the following 
-_€Xperiments were performed. RES 
A plate of red glass was placed in the aperture in the window 
shutter ; and at the distance of a couple of feet from it, was fixed a 
sheet of lead, having in it a round hole of a line in diameter. The — 
boundaries of the base of the cone formed by the rays, were accu- 
tately marked with a crayon on a sheet of white paper, at the dis- 
tance of twelve feet from the leaden plate. On substituting blue for 
ted glass in the window shutter, the base of the blue cone was found 
‘0 occupy precisely the same space on paper as that of the red one. 
Yellow and violet glasses were employed, and. the cones which they 
formed were equal to those produced by red and blue. It is to -be 
temarked that these monochromatic cones do not differ in magnitude 
om the cone formed by compound solar light. The colored fring- 
s observed round the base of the cone of: white light, cannot of — 
Course be observed around the base of the monochromatic cone ; 
but instead of them, appear rings of different ‘intensities of color : 
towards the centre of the base the color is bright but dilute, and 
dark but concentrated around the circumference. 
the equality in the size of the cones might be supposed to 
arise from any difference or imperfection in the colored media, I 
Tecejved the analyzed rays, emerging from a prism, on a sheet of 
ee J 
tia 
