ON THE APPARENT FIGURE OF STARS. 95 



daily winding upj a thirty-hour clock would, on this account of 

 attraction, as well as for many other'good reasons, be the most 

 preferable of any. 



I am, Sir, 



Your most obedient Servant, 



T. REID. 



III. 



Jn Essay on the apparent Figure of Stars and luminous Ob- 

 jects, seen at a very great Distance, and under a very small 

 Diameter. By Mr. J. H. Hassenfeatz*. 



I 



N the year 1806, 1 laid before the physical and mathematical PJiperjomena of 



class of the Institute several observations on the phsenomena small^aper. 



of vision through small apertures; and from them I have ex- tures. 



traded the following, on the apparent figure of stars, which 



are here brought together in one paper. 



If we look with the naked eye at a very remote lurai- Luminous 



I • , , 1 „ objects seen at 



nous object ; a star, a planet, a torch, a candle, or even a ^ ji,stance 



house on fire j we perceive, that these bodies are surrounded 



with rays of light, having particular directions ; and that these 



rays prevent our distinguishing and ascertaining the figure of 



the object. 



The number of these rays differs to different eyes : but two The rays from 

 rays, AB, AC, pi. II, fig. 1, in the direction of the eyes, are j-^^^j^'^ ^y^" 

 pretty generally observed ; as also a third, AD, perpendicular to 

 them. Some distinguish a fourth ray, AE, which is a prolon- 

 gation of AD : others see a fifth, AF, fig. 2 : and in certain 

 circumstances the spectator observes six or eight, fig. 3. 



V/hen the luminous body is so near the spectator, that he can The com- 



approach it, he may see this phaenomenon commence and in- ""'-"'^^'^ent 



f » ' ^ *■ and progress 



crease. of this phaeno- 



On receding from a candle to the distance of distinct vision, "^^"°" '^^' 



its figure is commonly that of a spear head, fig. 4. On receding ^ 



* Ann. deChim. vol. Ixxii, p., 5. 



farther^ 



