VOL. XLI.] PHILOSOPHICAL TRANSACTIONS. 443 



moment ; the wounds, by the care and skill of her surgeons, healed ; and she 

 recovered perfectly, except a numbness and contraction she had in some of the 

 fingers of both hands, and both feet and toes. 



An Account of M. Leuwenhoek's Microscopes. By Mr. Henry Baker, F. R. S. 



N° 458, p. 503. 



Martin Folkes, Esq. in N° 380 of these Transactions, gave such an exact 

 and full description of the structure and uses of these glasses, as left little more 

 for Mr. B. to offer, than a calculation of their magnifying powers, some re- 

 flections arising from such calculations, and a brief account of what improve- 

 ments in microscopes had lately been made. 



In order to this, he first viewed attentively the objects applied to these mi- 

 croscopes by M. Leuwenhoek himself, which Mr. Folkes has given a list of in 

 his account ; but the greatest part of them were destroyed by time, or struck 

 off by accident ; which indeed is no wonder, as they were only glued on a pin's 

 point, and left quite unguarded. Nine or ten of them, however, are still re- 

 maining ; which, after cleaning the glasses, appeared extremely plain and dis- 

 tinct, and proved the great skill of M. Leuwenhoek, in adapting his objects 

 to such magnifiers as would show them best, as well as in the contrivance of 

 the apertures to his glasses, which, when the object was transparent, he made 

 exceedingly small, since much light in that case would be prejudicial ; but, 

 when the object itself was dark, he enlarged the aperture, to give it all possible 

 advantage of the light. The lens being set so as to be brought close to the eye, 

 is also of great use, since thereby a larger part of the object may be seen at 

 one view. 



All these microscopes are of one and the same structure, and that the most 

 simple possible, being only a single lens, with a moveable pin before it, on 

 which to fix the object, and bring it to the eye at pleasure. 



Though it must cost much trouble to measure the focal distances of these lQ 

 microscopes, and thence ascertain their powers of magnifying, yet without that 

 it would be impossible to form a right judgment of them, or make any reason- 

 able comparison between them and others. This task therefore Mr. B. per- 

 formed, with as much care and exactness as he was able ; and has shown, in the 

 following table, how many of them have the same focus, and consequently 

 magnify in the same degree ; how many times they magnify the diameter, and 

 how many times the superficies of any objects applied to them. The calcula- 

 tions are given in round numbers, the fractions making but an inconsiderable 

 difference. 



3 l2 



