328 Intelligence and Miscellaneous Articles. 



like a circle, but very irregular, on account of the unsteadiness of the 

 movement communicated by the hand. 



Such is the principle that has led me to the construction of the 

 instrument I am going to describe, and which communicates the 

 perfect circular motion that it is impossible to impart by the hand. 



I establish on the top of a stand a conical tube, lying horizontally 

 at each end upon two vertical wheels, by which it is steadily sup- 

 ported. These wheels revolve in a groove, cut on the tube at each 

 of its extremities. By means of these grooves, and the wheels on 

 which the tube is supported, we can make it revolve freely and 

 regularly upon its axis. In the middle of the tube there is another 

 groove, in which an india-rubber ring is enrolling itself and from 

 thence passing on a large grooved wheel which, being turned by 

 means of a crank, impresses a rotatory motion on the tube. Inside 

 the tube I place a small telescope or an opera-glass, the eye-glass of 

 which is exactly centrical with the small end of the conical tube ; 

 while the object-glass is placed in an eccentric position by means of 

 two screws fixed on the two extremities of the diameter of the large 

 end of the tube. The axis of the telescope can be so inclined as to 

 take various degrees of eccentricity, so that, while the whole machine 

 makes the conical tube revolve upon its axis, the axis of the tele- 

 scope revolves round the former in an eccentric direction. 



The eccentric motion of the telescope is such that any star cor- 

 responding with the axis of the external tube is refracted through the 

 object-glass, and its rays dispersed as if that object-glass were a re- 

 volving prism ; and during that revolution the image of the star 

 describes upon the retina a circle proportionate to the eccentricity of 

 the telescope. 



If, while the telescope is revolving, we look into it with one eye, 

 we may with the other see the star ; and from this binocular vision 

 we have the phenomenon of a star revolving round another star, 

 forming a perfect luminous circle with a luminous point at its cen- 

 tre. This is a very curious observation, independently of the more 

 curious and interesting object of the instrument, which is to deve- 

 lope an infinitely small spot of light into a large circle, exhibiting 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. We have, in fact, a kind of 

 spectroscope, by which we can analyse the particular light of any 

 star ; and, further, by this instrument we may arrive at the discovery 

 of the real cause of the scintillation, and compare its intensity in 

 various climates and at different altitudes of a given star. At all 

 events the instrument will be found to be a curious application of 

 optics, and in proper hands may perhaps afford the means of making 

 many interesting observations and experiments upon the constitution 

 and properties of the light of the stars, so difficult to examine by the 

 spectroscope. I hope the idea will be fruitful, and not end trivially 

 in the contrivance of a mere scientific toy. 



