238 Mr. Brougham's Experiments and Observations on 
sun ; they had parallel sides pretty distinctly defined, but the 
ends were confused and semicircular, like those of the pris- 
matic spectrum. Like it too, they were oblong, and in some 
the length exceeded the breadth six, even eight times ; 
the breadth was, as I found by measurement, exactly equal to 
that of the sun's image received on a chart, as far from the 
pin as the image was, and the length was always to the 
breadth at all distances, in the same ratio, but not in all po- 
sitions of the pin ; for if it was moved on its axis, the images 
moved towards the shadow on one side, and from it on the 
other, becoming longer and longer (the breadth remaining the 
same) the nearer they came to the shadow on the one side, 
and shorter in the same proportion, the farther they went 
from it on the other. 
Obs. 3. Having picked out an image that appeared very bright 
and well defined, I let it through a hole with moveable sides, 
in the upper part of a sort of desk, which moved to any open- 
ing by hinges, and had a chart for its under side, on which 
the image fell, and I shut the hole so close as to prevent any 
of the others from coming through ; I then had a full oppor- 
tunity of examining it, in all respects, and I counted in it dis- 
tinctly the seven prismatic colours ; the red was farthest from 
the shadow of the pin, and from the pin itself ; then the 
orange; then the yellow, green, blue, and indigo, and the violet 
nearest of all ; in short, it was exactly similar to a prismatic 
spectrum, much diminished in length and breadth, and turned 
horizontally on the wall opposite to the prism, with the red 
farthest away. In fig. 5. se is the pin, reflecting the rays CP 
and CO, which pass through PO, the hole in the desk ED, to 
the chart or bottom of the desk RTSD, and form there the 
