The Flagella of Bacterium termo. By W. H, Ballinger. 175 
(3) The mean value of fifty measurements made with the 
ii^ch objective gives 0 • 0000048t^024. 
(4) The mean value of fifty measurements made with the 
inch objective gives 0'00000488200. 
We thus obtain a mean from the whole four sets of measure- 
ments, which gives for the value of the diameter of the flagellum 
of B. termo 0 * 00000488526, which expressed in vulgar fractions 
is equivalent to -^o of an inch nearly ; that is to say, within 
a wholly inappreciable quantity. 
Now if we suppose that as the method is only an approximate 
one, and the errors are entirely on one side, which I know no 
reason for doing, and therefore in round numbers reduce this 
fraction to the of an inch, it nevertheless provides us 
with a fact of much interest ; and indicates, as I believe, that an 
atom of ^evoi-transjparent structure the 2 ooVoofli of an inch may 
become visible under proper conditions of illumination and general 
manipulation. How far this is the actual limit with transparent 
or nearly transparent objects, I will not venture to aflSrm. But I 
am inclined to believe that it comes very near to it. But why, 
whether from the limitations involved in the nature of the lumini- 
ferous aether, and the conditions of light vibrations, it is not my 
province to pronounce. 
The calculations of which this paper gives the results have been 
carefully revised by my friend Mr. 0. H. Steam, of Liverpool 
