354 Oji the Refraction of Light. 



figure of the pyramid was varied, and the base on the paper describ- 

 ed, according to the position of the prism, a square, a rhomb, a 

 rhomboid, a trapezium, or a parallelogram. All the figures were 

 quadrilateral, and terminated by right lines. These phenomena 

 would lead us to consider the spectrum in an entirely new light j for 

 if we- admit the Newtonian hypothesis, that it consists of circular 

 images of the sun, the appearance of these luminous pyramids must 

 remain inexplicable. The idea that the spectrum consists of mono- 

 chromatic circles, the diameter of one of which forms its breadth, 

 and whose circumferences bound it on all sides, is a beautiful con- 

 ception, but it appears inconsistent with the luminous pyramids, 

 and with the following fact, which I accidentally discovered. 

 Whilst experimenting on the effects of transmitting the analyzed 

 rays emerging from a prism, in a dark room, through a bi-convex 

 lens, I chanced to interpose the lens between the sun and the prism, 

 in such a manner that the focus fell on the prism near its refrac- 

 ting angle. On the opposite wall I V0.s surprised to see a spec- 

 trum of a very peculiar and novel appearance. The proportion be- 

 tween its length and breadth exactly corresponded to that of the 

 Newtonian Spectrum, it being about five times longer than it was 

 broad ; but unlike the Newtonian image, its length lay in a direction 

 parallel with the length of the prism. In this spectrum the colors 

 are arranged longitudinally, in the order of the common spectrum, 

 and consequently all the dimensions of the common one are reversed 

 in this. Newton, from the circumstance of his not having succeeded 

 in attempts to increase the breadth of the spectrum, concluded that 

 its breadth was tlie diameter of one monochromatic circle ; but if we 

 grant that the breadth of this spectrum is formed by the diameter of 

 a colored circle, we must admit that that circle is painted with the 

 seven primitive colors, which, from a consideration of both spec- 

 tra, would be absurd. The Jines bounding the extremities of the 

 common spectrum, form the lateral boundaries of this new one ; and 

 its extremities are terminated by lines, which bound the long sides 

 of the Newtonian spectrum. The lines which bound the extremities 

 of the common spectrum are so produced in this image as to termi- 

 nate its long sides with straight hues ; and as it is certain that a curve 

 line on being produced cannot form a straight line, so it is certain that 

 all the boundaries of the solar spectrum are right lines. In order to 

 examine this spectrum minutely, the prism should be fixed on a stand, 

 the lens mounted on a swivel, and the white surface placed at a suit- 



