NATURAL PHILOSOPHY. 147 







signed by astronomers. The extraordinary agreement of the results 

 obtained in the three ways, from observation on the eclipses of the 

 satellites of Jupiter, from the phenomena of aberration, and from ac- 

 tual experiment, leaves no doubt that light does really travel with the 

 enormous velocity of about 192,000 miles per second. 



Soon after the above announcement was made by M. Fizeau, he 

 received the cross of the Legion of Honor, as a reward for Ms inge- 

 nuity. 



NEW OPTICAL INSTRUMENT. 



PROFESSOR JOHN LOCKE has invented a curious instrument, named 

 by him Phantascope, which will illustrate, in a manner never before 

 accomplished, " single vision by each eye." It is very simple, and 

 has neither lenses, prisms, nor reflectors. It consists of a flat board 

 base, about nine by eleven inches, with two upright rods, one at each 

 end, a horizontal strip connecting the upper ends of the uprights, and a 

 screen or diaphragm, nearly as large as the base, interposed between 

 the top strip and "the tabular base, this screen being adjustable to any 

 intermediate height. The top strip has a slit one fourth of an inch 

 wide and about three inches long from left to right. The observer 

 places his eyes over this slit, looking downward. The movable 

 screen has also a slit of the same length, but about an inch wide. 

 There are two identical pictures of a flower, about one inch in diam- 

 eter, placed the one to the left and the other to the right of the centre 

 of the tabular base, or board forming the support, and about two and 

 a half or three inches apart from centre to centre. A flower-pot or 

 vase is painted on the upper screen, at the centre of it as regards 

 right and left, and with its top even with the lower edge of the open 

 slit. By looking downward through the upper slit, and directing both 

 eyes steadily to a mark, a quasi stem, in the flower-pot or vase, in- 

 stantly a flower similar to one of those on the lower screen, but of half 

 the size, will appear growing out of the vase, and in the open slit of 

 the movable screen. On directing the attention through the upper 

 screen to the base, this phantom flower disappears, and only the two 

 pictures on each side of the place of the phantom remain. The phan- 

 tom itself consists of the two images painted on the base, optically 

 superimposed on each other. If one of these images be red and the 

 other blue, the phantom will be purple. If two identical figures of 

 persons be placed at the proper positions on the lower screen, and the 

 upper screen be gradually slid up from its lowest point, the eye being 

 directed to the index, each image will at first be doubled, and will 

 gradually recede, there being of course four in view until the two con- 

 tiguous coincide, when three only are seen. This is the proper point 

 where the middle or double image is the phantom seen in the air. If 

 the screen be raised higher, then the middle images pass by each oth- 

 er, and again four are seen, receding more and more as the screen is 

 raised. As all this is the effect of crossing the axes of the eyes, it 

 follows that a person with only one perfect eye cannot make the ex- 

 periments. They depend on binocular vision. 



