3 5$ -Mr. Brougham’s Experiments and Obsewations 
scratches and opaque veins, but like most glass that is not finely 
wrought, having its surface of a structure somewhat fibrous. 
When this tube was slowly introduced into the light, and so 
held that none of the rays might be refracted, a streak, chiefly 
white, was seen, similar in shape and position to those de- 
scribed before.* When narrowly inspected, it was found to 
contain many images by reflexion in it. But these were much 
diluted by the abundance of white light, reflected without de- 
composition in the manner above mentioned. -f This streak 
lay wholly on one side of the tube ; but I moved the tube on- 
ward a little, and another streak darted through the shadow, 
and extended all round on both sides : and now, when the tube 
was in the middle of the rays, there were two streaks on both 
sides, one a little separated from the other and continued 
through the shadow, the other on each side of the shadow ; the 
former was evidently produced by refraction ; it contained 
many images very like those by reflexion, only more vivid in 
the colours, which were all in the inverted order, the violet 
being outermost, and the rest nearest the point of incidence. 
Images similar to these are also producible on the retina, as 
mentioned before. £ 
Observation 6. I now placed a prism at the hole, and made 
the same images by refraction, out of homogeneal light. These 
inclined to the red, not (like images by reflexion) to the vio- 
let ; but they were broadest in the red, and grew narrower to- 
wards the violet parts. In short, when viewed beside the 
images by reflexion, except in point of brightness and inclina- 
tion they differed from them in no respect. 
The three first experiments shew, that when homogeneal 
* Phil. Trans. 1796, page 236, f Ibid. p. 237. % Ibid. p. 243. 
