552 PHILOSOPHICAL TRANSACTIONS. [aNN0 1710» 



needle, but must unavoidably drop; and wherever it happens to fall, it must, in 

 that almost liquid state, receive impressions sufficient to spoil the figure of a 

 sphere. 



Mr. Gray has shown the defect of his method, which he used to recover by 

 grinding and polishing his glasses on a brass plane, and so reduce them to 

 hemispherules ; but how far short polished glasses (I speak of small ones) come 

 of those which are cast, I leave to any one to judge who has seen both. His 

 water and quicksilver microscopes I never saw, so can say little to them. 



After what manner Mr. Wilson's glasses are made, I know not; but sure his 

 greatest magnifiers are ill placed, being sunk to so great a distance from the eye, 

 the object cannot appear to that advantage it otherwise would. If therefore, 

 instead of a hollow cap, he would contrive a plain plate of any metal, for the 

 reception of the glass, then the eye and the object might come to their due 

 distance: neither ought there to be any calx or glass between the object and the 

 spherule, when we use the greatest magnifiers, because if the focus of a sphere 

 be at the extremity of its circumference, any small distance from that must spoil 

 the truth of the object's appearance. 



I cannot say, that the glasses I have made are without fault, but I think they 

 magnify more than any I have yet seen ; and were they placed to the best ad- 

 vantage, they would magnify much more than they do : they are made thus. I 

 take a piece of fine window glass, and I raise it with a diamond into as many 

 lengths as I think needful, not exceeding an eighth of an inch in breadth ; then 

 holding one of these lengths between the fore-finger and thumb of each hand, 

 over a very fine flame, till the glass begin to soften, I draw it out till it be as 

 fine as a hair and break : then inuring each of the ends into the purest part of 

 the flame, I have two spheres presently, which I can make larger or smaller as 

 I please : if they remain long in the flame, they will have spots, so I draw them 

 out presently after they turn round. As for the stem, I break it off as near the 

 ball as 1 can, and lodging the remainder of this stem between the plates, and 

 by drilling the hole exactly round, all this protuberance is buried between the 

 plates, and the microscope performs to admiration; so that the same thread of 

 very fine muslin appeared 3 or 4 times larger in one of these, than it did in the 

 first or second of Mr. Wilson's. I thought I saw animals in fine old brandy, 

 but they were so nimble in their motion, that I can give no particular descrip- 

 tion of them. Human blood is so far from showing any red globules swimming 

 in serum, that immediately after its emission it appears to be a body of infinite 

 branches, running in no certain order, variously coloured; where it lies thickest 

 on the glass, it is of a dull red; where thin, inclining to yellow; but the whole 

 so blended, as to represent very nearly the top of a yew-tree in a very fine 



