680 PHILOSOPHICAL TRANSACTIONS. [aNNO 1723. 



opened entirely new scenes in some parts of natural philosophy, as in that 

 famous discovery of the animalcula in semine masculino, which has given a 

 perfectly new turn to the theory of generation, in almost all the authors that 

 have since written on that subject. 



The construction of these instruments is the same in them all, and the 

 apparatus is very simple and convenient; they are all single microscopes, con- 

 sisting each of a very small double convex glass, let into a socket, between two 

 silver plates rivetted together, and pierced with a small hole; the object is 

 placed on a silver point, or needle, which, by means of screws of the same 

 metal, provided for that purpose, may be turned about, raised, or depressed, 

 and brought nearer, or put farther from the glass, as the eye of the observer, 

 the nature of the object, and the convenient examination of its several parts 

 may require. 



Mr. L. fixed his objects, if they were solid, to this silver point, with glue ; 

 and when they were fluid, or of such a nature as not to be commodiously 

 viewed unless spread upon glass, he first fitted them on a little plate of talk, 

 or excessively thin blown glass, which he afterwards glued to the needle, in the 

 same manner as his other objects. 



The observation indeed of the circulation of the blood, and some others, 

 require a somewhat different apparatus, and such an one he had, to which he 

 occasionally fixed these same microscopes ; but as it makes no part of this 

 cabinet, I shall omit giving any farther account of it, only taking notice that it 

 may be seen in a letter to the Royal Society, of the 12th of January, 1689, 

 and printed in his Arcana Naturae Detecta, N° 69. 



On the late Queen Mary's visiting Mr. L. at Delft, and viewing his curiosi- 

 ties with great satisfaction, he presented her with a couple of his microscopes, 

 which it seems were of the same sort as these, and no ways differing from one 

 of the 13 cases contained in the drawers of this cabinet. 



The glasses are all exceedingly clear, and show the object very bright and 

 distinct. Their powers of magnifying are different, as different sorts of ob- 

 jects may require; and as on the one hand, being all ground glasses, none of 

 them are so small, and consequently magnify to so great a degree, as some of 

 those drops frequently used in other microscopes; yet on the other, the dis- 

 tinctness of these very much exceeds what are met with in the glasses of that 

 sort ; and this was what Mr. L. ever principally proposed to himself, rejecting 

 all those degrees of magnifying in which he could not so well obtain that end; 

 having found in a long course of experience, that the most considerable disco- 

 veries were to be made with such glasses as, magnifying but moderately, exhi- 

 bited the object with the most perfect brightness and distinctness. 



