viewed by Microfcopes . 41 
true Size ; nor can we, indeed, come to any 
certain Conclufion as to that, but by the 
Mediation of fame larger Objedt, whole 
Dimenfions we really know. For as Bulk 
itrfelf is merely comparative, the only Way 
we can judge of the Bignefs of any thing is, 
by comparing it with fomething elfe, and 
finding out how many Times the lefier is 
contained in the larger Body. To do this 
in Microfcopical Objects, feveral ingenious 
Methods have been contrived; of which, 
fuch as are come to my Knowledge, and are 
plain and pra&icable, I jfhall lay before the 
Reader. 
Mr. Leeuwenhoek’s Way of comput¬ 
ing the Size of Salts in Fluids, of the Ani¬ 
malcules in Semine Mafculino , in Pepper- 
Water , &c. was, by comparing them with 
the Bignefs of a Grain of Sand *; and his 
Calculations were made in the following 
Manner. 
* 
* N. B. It is proper to inform the Reader, that when¬ 
ever, in this Treatife, Microfcopical Objedts are compared 
with a Grain of Sand, which commonly was the Meafure 
Mr. Leeuwenhoek, made ufe of, we muft underftand it to 
mean a Grain of coarfe Sea-Sand (ufually called Scouring - 
Sand) which is equal in Bignefs to feveral Grains of our 
common Inland Houfe-Sand, or IVriiing-Sand. But to make 
our Calculation ftill more certain, we muft fuppofe them of 
fuch a Size, that an hundred of them placed in a Row fhali 
extend an Inch in Length. 
He 
