and Locality o/" Muscae volitantes. 3 



distinctness, we must look at the sky, or a lutninons object, 

 either through a very minute aperture, or, when tlie light is 

 limited or feeble, through a lens or microscopic doublet, of 

 very short focus, held close to the eye. By this means we 

 shall observe a luminous ground, covered, more or less, with 

 transparent filaments or tubes, transparent circles, exceedingly 

 minute, and (when they do exist) with Muscat, or black spots 

 like flies. 



In examining the transparent filaments, I have observed 

 them o^four or Jive different sizes, the smallest of which are 

 the most distinct. Tiiese distinct filaments are bounded by 

 two sharp black lines, and the space between them is more 

 luminous than the general ground on which they are seen. In 

 the larger filaments, the black lines are coloured at their edges, 

 and, on the outside of each of them, are one or more coloured 

 fringes. 



Tlie minute transparent circles, when smallest, have a lumi- 

 nous centre, with a sharp black circle round it. In the larger 

 ones, this circle is coloured at its edges; and, on the outside 

 of it, are one or more circular coloured fringes. These sphe- 

 rical bodies sometimes exist singly, and sometimes in groups, 

 partly connected by small filaments, and partly by an invisible 

 film, to which they seem attached. They sometimes adhere 

 to the outside of the filaments, and very frequently occur within 

 the filaments, so as to prove that these filaments are tubular. 

 These spherical bodies have, like the filaments, yo?<r ov Jive 

 different sizes. 



In making observations on these spherical bodies, the ob- 

 serverwill sometimes see luminous spots pass through the field; 

 but as these arise from the state of the lubricating fluid on the 

 outside of the cornea, they have no connexion with the phae- 

 nomena under our consideration. 



The transparent filaments, already described, are seldom 

 seen single. Two or three are united, like threads crossing 

 one another; and sometimes a great number are united, like 

 a loose heap of thread, in which case obscure spots appear at 

 the places where the crossings of the filaments are most nu- 

 merous. 



In some cases a single loner filament is once or twice dou- 

 bled up upon itself, and sometimes a knot is, or appears to be, 

 tied upon it, consisting of several folds, as it were, of the fila- 

 ment. This knot has several very dark spots at the places 

 where the diflerent portions of the filament are in contact ; 

 and this accumulation, as it were, of black specks, constitutes 

 tlie real Musca;. In many, indeed in almost all of these Muscle, 

 v/hen distinct, a little bright yellow light accompanies the 

 black specks. 



B2 



