LETTER 18. RAIN-WATER 123 
On the 31st ditto, I discovered more little animals in 
the water, as well as a few that were a bit bigger; and I 
imagine that ten hundred thousand of these very little 
animalcules are not so big as an ordinary sand-grain.’ 
Comparing these animalcules with the little mites in cheese 
(which you can see a-moving with the bare eye), I would 
put the proportion thus: As the size of a’small animalcule 
in the water is to that of a mite, so is the size of a honey- 
bee to that of a horse; for the circumference of one of 
these same little animalcules is not so great as the thick- 
ness of a hair on a mite. 
The 4th Observation. Rain-water. 
On June 9th,’ collected rain-water betimes in a dish, as 
aforesaid, and put it at about 8 o’clock in the morning in 
a clean wine-glass, and exposed it to the air at about the 
height of the third storey of my house, wondering whether 
the little animals would appear sooner in water thus 
standing in the air. 
The 10th ditto, observing this water, I fancied that I 
discovered living creatures; but because they were so 
few, and not so plainly discernible, I could not accept 
this for the truth. 
On the 11th ditto, seeing this water, with the naked 
eye, stirred in the glass by a stiff gale of wind (which had 
now blown from the same quarter for 36 hours; the 
weather being so cold withal, that it did not irk me to 
wear my winter clothes), I had no thought of finding any 
living creatures in it; but upon examining it, I saw with 
wonder quite 1000 living creatures in one drop of water. 
‘This means that he estimated their diameter at something less than 
zdo of the diameter of an “ordinary” (or large) sand-grain. Taking this 
as 35 of an inch, their diameter would thus be of the order of so00 in., or 
roughly 8°5. This is a very close guess at the size of Monas vulgaris. On 
sand-grains cf. p. 334 fra. 
? Anno 1676. 
