STEPHEN GRA Y, 1696. LEEUWENHOEK, 1703. IJ 



words, of Stephen Gray's account of his discoveries in these several direc- 

 tions is herewith subjoined : 



" I know not well how at this time to account for this strange phenomenon, that 

 an object should be placed so far within the focus of a spherule, as to be within the glass, 

 and yet seen distinctly to the eye so near it ; but since by matter of fact, I found it was 

 so, I made this inference, and concluded, that if I conveyed a small globule of water 

 to my eye, and that there were any opacous or less transparent particles than the 

 water therein, I might see them distinctly. 



" Exp. 4. Having by me a small bottle of water, which I knew to have in it some 

 of those minute insects, which the deservedly famous observator Mr. Leeuwenhoek dis- 

 covered, by the help of excellent microscopes. Having seen them with the common 

 glass microscopes, and with the first aqueous, as above mentioned, I poured a few drops 

 of this water on the table, and taking a small portion thereof on a pin, I laid it on the 

 end of a small piece of brass wire, of about one-tenth of an inch diameter. I con- 

 tinued to lay on two or three portions of water, till there was formed somewhat more 

 than an hemispherule of water ; then keeping the wire erect, I applied it to my eye, 

 and standing at a proper distance from the light, I saw them and some other irre- 

 gular particles, as I had predicted, but most enormously magnified ; for whereas they 

 are scarce discernible by the glass microscopes, or the first aqueous one, within the 

 globule, they appeared not much different both in their form, nor less in magnitude 

 than ordinary peas. They cannot well be seen by daylight except the room be 

 darkened, after the manner of the famous dioptrical experiment, but most distinctly 

 by candle-light; they may be very well seen by the full moon light, and the pin 

 sometimes takes up the water round enough to shew its objects distinct. 



" The insects I have yet this way observed, are of two sorts, globular and ellipti- 

 cal : I shall first describe the former. They are of a globular form, they are but a little 

 less transparent than the water they swim in ; they have sometimes two dark spots 

 diametrically opposite, but these are rarely seen ; there are sometimes two of these 

 globular insects sticking together ; where they are joined 'tis opacous, possibly they may 

 be in the act of generation ; they have a twofold motion, a swift progressive irregular 

 one, and at the same time a rotation on their axes at right angles to the diameter 

 that has the dark spots, but this is seen only when they move slowly. They are 

 almost of an incredible minuteness. Mr. Leeuwenhoek is moderate enough in his com- 

 putation, when he tells us * he saw insects in water, so small, that 30,000 could not 

 more than equal a coarse sand ; but I believe it will seem a paradox to him, when 

 one that tells him so shall at the same time say, that he can see them by only 

 applying the bare eye, to a portion of water wherein they are contained." 



In the year 1703 Leeuwenhoek contributed to the 'Philosophical Trans- 

 actions ' an account of several species of animalcules observed by him on 

 the roots of duckweed obtained from the River Maes at Delf-haven in 

 Holland, which was accompanied by woodcut illustrations of the various 

 forms encountered. Among them are especially conspicuous a species of 

 Vorticella, apparently V. nebulifera, and a tube-dwelling variety allied to, 

 if not identical with Vaginicola crystallina. In addition to the true Infusoria 

 above named, Leeuwenhoek figured and described for the first time the Fresh- 

 water Polyp (Hydra) and a large sedentary Rotifer most nearly resembling 

 Limnias ceratophylli. The majority of these types are represented as 

 adherent to a single rootlet of duckweed, having interspersed among them 

 several acicular diatoms (Fragillaria), and a few other exceedingly minute 

 stalked particles referred to by him as " little flower-like figures," and which 



* ' Phil. Trans.,' No. 213, p. 198. 



