NATURAL PHILOSOPHY. 101 



placed horizontally on a stand, and revolving on its own axis by 

 means of wheels ; inside this tube, a telescope or an opera-glass is 

 placed, by which, by means of two opposite screws, the end of the 

 object-glass can be placed in an eccentric position in various degrees 

 according to the effect desired, while the eye-glass remains in the 

 centre of the small end of the tube. Now, if we understand that 

 when the machine makes the tube to revolve upon its axis, the tele- 

 scope inside revolves in an eccentric direction, during the revolution 

 the star seen through it must appear like a circle. This circle exhibits 

 on its periphery the various rays emitted by the star, all following each 

 other in spaces corresponding with their duration, showing also blank 

 spaces between two contiguous rays which must correspond with the 

 black lines of the spectrum. The instrument, in fact, is a kind of spec- 

 troscope, by which we can analyze the light of any star, study the 

 cause of the scintillation, and compare its intensity in various climates 

 or seasons and at different altitudes. Proc. " British Association" 

 1863. 



SOME PHENOMENA PRODUCED BY THE REFRACTIVE POWER OF 



THE EYE. 



In a paper read before the British Association, 1863, by Mr. A. 

 Claudet, the author gave an explanation of several effects of the re- 

 fraction of light through the eye ; one of which is, that objects 

 situated a little behind us are seen as if they were on a straight line 

 from right to left. Another, that the pictures of external objects 

 which are represented on the retina, are included in an angle much 

 larger than one-half of the sphere at the centre of which the observer 

 is placed ; from this point of view a single glance encompasses a vast 

 and splendid panorama extending to an angle of 200. This is the 

 result of the common law of refraction. All the rays of light passing 

 through the cornea to the crystalline lens are more and more refracted 

 in proportion to the angle at which they strike the spherical surface 

 of the cornea. Consequently, the only objects which are seen in their 

 true position are those entering the eye in the direction of the optic 

 axis. By this refraction, the rays which enter the eye at an angle of 

 90 are bent at 10, and appear to come from an angle of 80. This 

 phenomenon produces a very curious illusion. Where we are lighted by 

 the sun, the moon, or any other light, if we endeavor to place our- 

 selves in a line with the light and shadow of our body, we are sur- 

 prised to find that the light and the shadow seem not to be connected 

 at all, and that, instead of being in a line, they appear bent to an 

 angle of 160 instead of 180, so that we see both the light and the 

 shadow a little before us, where they are not expected to be. The 

 eye refracts the line formed by the ray of light, and the shadow and 

 the effect is like that of the stick, one-half of which being immersed in 

 water, appears crooked or bent into an angle at the point of immer- 

 sion. This enlargement of the field of vision to an angle of 200, is 

 one of those innumerable and wonderful resources of nature by which 

 the beauty of the effect is increased. Our attention is called to the 

 various parts of the panorama which appear in any way a desirable 

 point of observation, and we are warned of any danger from objects 

 coming to us in the most oblique direction. These advantages are 

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