30 07i the Halo seen around all Bodies. 



cause of onr not seeing objects through it. The continued action 

 of hght destroys certain comMnations which develop colors, and 

 thus decomposes them ; but light has no such annihilating power 

 as Newton assigned to it. It is the opacity of accumulation 

 which hides colored bodies from our sight ; light has no power 

 to decompose or annihilate instanter ; on the contrary, there are 

 certain qualities in the black principle which annihilates light 

 itself. 



39. There is an experiment of painting the different colors on 

 the periphery of a wheel, and it has become a settled question in 

 optics that these colors all blend into a white mass as soon as the 

 wheel is in rapid motion. It is known that the duration of im- 

 pression, on the organs of vision, are very limited ; we cannot 

 wonder therefore, that the feeble rays of light which are to give 

 an impression of the colored patches on the wheel, should fail in 

 doing so. As the rapidity of motion prevents the duration of 

 impression of the feebler rays of colored objects, nothing remains 

 perceptible to vision but the dense mass of light from the whole 

 circumference of the wheel. 



40. If on one side of a card — as in the beautiful experiments 

 of Dr. Paris — we paint a head, and on the other side a body, by 

 making the card turn rapidly, the head appears to be attached to 

 the body. The feeble rays proceeding from that edge or hne of 

 the circumference which passes before the eye at every half rev- 

 olution, are lost in the mass of light which is reflected from the 

 colored and white portions of the card. But if the card be made 

 to turn very rapidly, even the figures are hidden, because, as has 

 been observed, the duration of impression is very limited. 



41. A pin-hole at a little distance appears very small, but the 

 aperture increases as the distance decreases. It is only when the 

 pin-hole is close to the eye, that the true magnifying or lenticular 

 power of the halo is recognized. It will be then perceived that 

 it completely occupies the whole opening, and that objects which 

 are held between the eye and the pin-hole, will all be inverted, 

 not only inverted both as to position and movement, but also pos- 

 sessing a much larger outline than the objects themselves. This 

 aperture, therefore, is a lens whose magnifying power is accord- 

 ing to the size of the apertme and its distance from the eye. 



42. On looking through the halo as it fills up the pin-hole, we 

 shall perceive that objects beyond it are very distinctly seen, and 



