the Croonian Lecture. 
187 
sufficiently dilute was placed under the microscope, and 
being viewed with both eyes open, a globule of blood ap- 
peared to occupy, in the first experiment, one half of one 
tenth of an inch, and in the second experiment, one third of 
one tenth of an inch upon the ruler. Hence the size of the 
globule by the first experiment will be equal to 
£ °f of of 1 inch = of an inch ; 
and by the second experiment 
£ of ^ of ~ of 1 inch = of an incl H 
the mean of which, or ^ of an inch, may be considered 
as about the mean diameter of a globule of the blood. 
This measurement of Captain Kater’s, as it was natural 
to expect, corresponds with that which has been made by 
Dr. Wollaston, by means of a very ingenious micrometer 
of his own invention, a description of which has a place in the 
Philosophical Transactions; and with the measurement of Dr. 
Young in his eirometer, of which he has given an account in 
his Introduction to Medical Education. 
The diameter of a globule of the blood, measured by 
mathematicians of such eminence, is to be set down as 
part of an inch; and the diameter in the micrometer, measured 
with all the accuracy that instrument is capable of, since such 
was the smallest apparent dimension which occurred in Mr. 
Bauer’s experiments, as - 0 k 0 - 5 part of an inch. 
I have taken more pains to have the difference between the 
measurement of a globule in these different modes ascertained, 
than the subject would appear to require; but its being known, 
will enable microscopical observers, unskilled in the higher 
branches of mathematics, to pursue their observations upon 
globules of different sizes, and continue to compare their re- 
