On the Appearance of the Stars when viewed Cursorily. 2ST 



ist) to give it the milky appearance for which it has so long 

 been famous. By our indirect glances during a careless re- 

 view of the heavens, thousands of these minute objects are 

 sufficiently increased in apparent diameter, as I shall present- 

 ly mention, to make a sensible impression on the retina of the 

 eye; and from the false glare surrounding each point, and 

 the closeness of the stars, they appear, in many cases, abso- 

 lutely in undefined contact, necessarily producing the appear- 

 ance which the galaxy presents, and very similar to what I have 

 already observed, and any one may convince himself of it, in 

 the Pleiades. Other parts of the heavens present similar facts, 

 of which I may notice that the frequent small clusters in the 

 stream of Aquarius are favourable examples. 



There are two opinions regarding the physical cause of the 

 phenomenon ; the one is that of Messrs Herschel and South, 

 and also probably of the first observers of the fact, the French 

 astronomers. They conceive, that " the lateral portions of the 

 retina, less fatigued by strong lights, and less exhausted by 

 perpetual attention, are probably more sensible to faint im- 

 pressions than the central ones. 1 ' Now, were we to stand by 

 this explanation, my generalization of the fact must fall to the 

 ground ; for in such a survey of the heavens as I speak of, the 

 retina cannot be said to be " fatigued by strong lights," or 

 " exhaustedjby perpetual attention. r> * Or, on the other hand, 

 if my adoption of the principle is acknowledged to be correct, 

 the explanation of these gentlemen is untenable. We therefore 

 look to the second method of accounting for it, by Dr Brews- 

 ter, who observes that " a luminous point seen indirectly, 

 swells into a disk, and thus loses its sharpness, and acts 

 upon a greater portion of the retina ;"" and he adds in a note, 

 that this advantage of expanded vision does not give the co- 

 lours of the point truly ; we therefore only gain a knowledge 

 of its existence, and an idea of its situation. This last expla- 

 nation applies equally in both cases ; for the stars are indivi- 

 sible points, whether viewed by the telescope or the naked 

 eye, and we thus receive a confirmation of the correctness of 



* Our correspondent, we suspect, mistakes the meaning of this passage 

 in Messrs Herschel and South's paper. The exhaustion, we presume, here 

 rt Terred to, is a permanent effect, supposed to be produced upon the cen- 

 tral parts of every retina. — Ed. 



