TOL. XLr.] PHILOSOPHICAL TRANSACTIONS. 445 



pedestal, from which a turning specuhim reflects the light upwards upon the 

 object : it is likewise contrived to be used with the apparatus of the solar mi- 

 croscope. Descriptions and figures of both of which are given in Mr. B's book 

 intitled, The Microscope made easy. Edit. 2d. Lond. 1743, 8vo. 



Mr. B. measured the focal distances, and magnifying powers, of the 6 glasses, 

 and found them to be as follows : 



A Table of the Six Magnifiers belonging to Mr, Folke/s Microscope, calculated 

 by an Inch Scale divided into a hundred Parts, with a Computation of their 

 Powers, to an Eye that sees Objects at 8 Inches. 



Glasses. Distance of Magnifies the Magnifies the 



the Focus. Diameter. Superficies. 



1st -^ of an Inch 400 l60,000 



2d ^ 160 25,600 



3d ^ 100 10,000 



4th ^ 44 1,936 



5th ^ 26 676 



6th i 16 256 



The above calculation shows, that Mr. Folkes's first glass magnifies the su - 

 perficies of an object 6 times as much as the greatest magnifier of M. Leuwen- 

 hoek. And that the animalcula, a million of which, he says, scarcely equalled 

 a grain of sand, would, if viewed with this magnifier, appear as large as l6 

 grains of sand do to the naked eye. And M. Leuwenhoek must have had 

 glasses to magnify even more than this, though they are not come to us. For 

 we cannot otherwise conceive, how he could observe the animalcules in the 

 semen masculinum of a flea, and of a gnat, as we find he did, or assert, as he 

 does in the strongest terms, that he could see the minutest sort of animalcules 

 in pepper-water, with his glasses, as plainly as he could swarms of flies or gnats 

 hovering in the air with his naked eye, though they were more than ten mil- 

 lions of times less than a gr^in of sand. And lest this should be imagined only 

 a random guess, he gives immediately a regular arithmetical calculation to 

 prove his computation right. But we may all be sensible, that no glasses 

 in this cabinet are able to render such minute objects distinguishable. 



One thing alone (which, when slightly considered, may appear but trifling) 

 has conduced greatly to the modern improvements ; viz. the making use of fine 

 transparent Muscovy talc or isinglass, placed in sliders, to inclose objects in. 

 Had M. Leuwenhoek known this way, it would have saved him a vast deal of 

 expence and trouble. For then, we may reasonably suppose, instead of mak- 

 ing an entire and separate microscope for every object, he would probably have 



