IIARDWICKE'S SCIENCE-GOSSIP. 



Lens, or admitted nearer to it, by a little Screw, /, 

 that, passing through the Stage horizontally, and 

 bearing against the Back of the Instrument, thrusts 

 it farther off when there is occasion. The End of 

 the long Screw, g, comes through the Stage at m, 

 where it turns round, but acts not there as a Screw, 

 having no Threads that reach so high. 



" These microscopes are plain and simple in their 

 Contrivance. All the Parts are Silver fashioned by 

 Mr. Leeuwenhoek's own Hand ; and the Glasses, 

 which are excellent, were ground and set by himself. 

 He glued one, or at most two, Objects on the point 

 of the Pin belonging to each microscope, and care- 

 fully preserved them there; so that each Instrument, 

 being devoted to on'e or two Objects only, could be 

 applied to nothing else. This Method induced him 

 to make a Microscope with a Glass adapted to 

 almost every Object, till he had got some hundreds 

 of them, as he says himself in the 2nd vol. of his 

 Works, page 230, Mihi quidem sunt centum centum- 

 que Microscopia, &c. All this Trouble and Expence 

 is now saved by a Set of Glasses, to be shifted with 

 great Ease, as the Subject to be examined may 

 require. 



" The magnifying Powers of these Glasses come 

 short of some now made, but are fully sufficient for 

 most Purposes. Of the 26 Microscopes I examined, 

 one magnifies the Diameter of an Object 160; one, 

 133; one, 114; three, 100; three, 89; eight, 80; 

 two, 72 ; three, 66 ; two, 57 ; one, 53 ; and one, 

 40 times." 



These instruments, we need scarcely observe, 

 were much inferior to the cheapest English or con- 

 tinental microscopes of the present day, and it is a 

 matter of surprise that so much really good work 

 could be accomplished by tools of such inferior 

 quality. Of course a very large portion of the 

 microscopic Fauna and Flora with which we are now 

 acquainted was totally unknown to the microscopic 

 workers of that period ; Desmids and Diatoms 

 could not be, or at least were not, detected by such 

 aids as those just described. 



We now proceed to give a short resume of the 

 work accomplished by the " Great Leeuicenhoek." 



In the Preface to his " Select Works, containing 

 his Microscopical Discoveries," he remarks, that 

 " I have heard that many persons dispute the truth 

 of what I advance in my writings, saying that my 

 narrations concerning animalcules, or minute living 

 creatures, are merely my own inventions. And it 

 seems some persons in France have even ventured 

 to assert that those are not in truth living creatures 

 which I describe as discoverable to our sight, and 

 alledge that, after water has been boiled, those par- 

 ticles in it which I pronounce to be animalcules will 

 be still observed to move. For my own part, I will 

 not scruple to assert that I can place before my eye 

 the smallest species of those animalcules concerning 

 which I now write, and can as plainly see them 



endued with life as with the naked eye we behold 

 small flies or gnats sporting in the open air, though 

 these large animalcules are more than a million of 

 degrees less than] a large grain of sand. For I not 

 only behold their motions in all directions, but I 

 also see them turn about, remain still, and some- 

 times expire; and the larger kinds of them I as 

 plainly perceive running along as we do mice with 

 the naked eye. Nay, I see some of them open their 

 mouths, and move the organs and parts within 

 them; and I have discovered hairs at the mouths 

 of some of these species, though they were some 

 thousand degrees less than a grain of sand." * 



Leeuwenhoek means that the solid contents of a 

 grain of sand would be a thousand times greater 

 than the animalcule, and not that the animalcule 

 was a thousand diameters less than a grain of fine 

 sand. This is rendered evident by his remarks a 

 little further on: he says,— "In examining the in- 

 testines of flies and other insects by the micro- 

 scope, I have discovered vessels conveying the 

 blood and juices, the smallest ramifications or 

 branches whereof appear to me more than 200,000 

 times less than a hair of my beard." Supposing 

 the hair to be the ^V of an inch in diameter, the 

 highest magnifying power at his command would 

 not have enabled him to have discerned vessels 

 only the 2O0 ' 0O0 ' part of the 5 V of an inch Gnnnhroo 

 of an inch) if diameters were meant. 



His plan of obtaining the size of a minute object 

 is worth transcribing:— "I have a plate of copper 

 with many lines engraved on it, and divided into a 

 number of small equal parts. I then carefully 

 observe how many of these parts one hair taken 

 from my beard and seen through [the microscope 

 appears to cover. Supposing that the diameter of 

 this hair appears equal to fifty of those parts, then 

 with the point of a needle I trace on the copper a 

 line of the same size by the naked eye as is equal 

 to one of the small veins or vessels in a flyf seen 

 through the microscope, and I find nine of those 

 small veins so traced with a needle, when placed 

 close together, are the fiftieth part of the diameter 

 of the hair. If, then, 450 diameters of those small 

 veins which I most plainly see in a fly are no more 

 than equal to the diameter of one hair taken from 

 my beard, it follows by the rules of arithmetic^ that 

 one of such hairs is more than 200,000 times larger 

 than those very small blood-vessels in a fly." 

 (To be continued?) 



* The grain of sand he afterwards describes as being of the 

 kind called glass-grinder's sand. 



t Leeuwenhoek probably saw the tracheal tubes. 



t Now, the area ot circles being in proportion to the 

 squares of their diameters, the proposition may be thus 

 demonstrated : — 



450 

 450 



22500 

 18(10 



202,500 



