LEEUWENHOEK’S MICROSCOPES 331 
but he could not perform miracles. Moreover, there is no 
reason to suppose that he possessed any apparatus essentially 
different from that which is now known. (Blanchard’s sug- 
gestion (1868) that he destroyed his best instruments in his 
old age “with the idea of continuing to appear to everybody 
as an incomparable observer ”’, is. quite unjustifiable.) All the 
evidence indicates that it was the method of using this appar- 
atus which he ‘“‘ kept for himself alone’”’: his secret lay, as he 
tells us repeatedly, in his “ particular method of observing.” 
What can it have been? The answer is—to me—almost 
certain, though I cannot prove from his own words (since he 
tried not to give his secret away) that I am right. I am 
convinced that Leeuwenhoek had, in the course of his experi- 
ments, hit upon some simple method of dark-ground wllwmin- 
ation. He was well aware, as we know, of the ordinary 
properties of lenses; and he tells us himself that he used 
concave magnifying mirrors and employed artificial sources 
of illumination (e.g. a candle). Consequently, he may well 
have discovered by accident—or even have purposely devised 
—some method which gave him a clear dark-ground image. 
Such a discovery—possibly inspired by observing the motes. 
in a sunbeam—would at once explain all his otherwise inex- 
plicable observations, without supposing him to have possessed 
any apparatus other than that which we now know he had. 
But no hint was ever knowingly given, in all his many letters 
(so far as I have been able to ascertain), of what his “ par- 
ticular method of observing” may really have been. 
Nevertheless, there is, in a very early letter, a remark 
which seems to me to substantiate my interpretation—though 
one must, I think, be personally familiar with such things to 
appreciate it properly. Writing about red blood-corpuscles in 
1675, Leeuwenhoek (in reply to criticism) says :* 
. . . but I can demonstrate to myself the globules [= cor- 
puscles] in the blood as, sharp -and clean as one can 
distinguish with one’s eyes, without any help of glasses, 
sandgrains that one might bestrew upon a piece of black 
taffety silk. 
1 From Letter’ 9. 22 January 1675. To Oldenburg. MS.Roy.Soe. 
Unpublished. 
* The words I have here interpreted and italicized are, in the original, 
“desantgens . . . diemen op een swart sijde taff ‘soude mogen werpen”’. 
