ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
881 
For greater security against wear and tear, each ring is formed of 
two edges about 1/2 mm. apart. 
In other respects, viz. in the means for raising and lowering the 
scale and contact point, the apparatus is similar to the contact micro- 
meter, and so far differs from Mr. Nelson’s instrument, that no micro- 
meter-screw, with its possible errors of back-lash, &c., is made use of. 
The error, common to all spherometers, and due to the fact that the 
contact circle of steel ring and spherical surface is not exactly coincident 
with the edge, so that the measurement of h for concave surfaces is too 
low, and that for convex surfaces too high, is found to diminish the 
greater the diameter of the ring. Accordingly, a ring of the largest 
possible diameter should always be used, and, in the case of lenses with 
surfaces of equal but opposite curvatures, the mean of the readings for 
the convex and concave surfaces should be taken as the value of h. 
(6) Miscellaneous. 
The Microscope as an Aid to Physiology. — Canon Wilberforce 
having stated that the discovery of the circulation of the blood was due, 
not to Harvey, but “ by means of putting the foot of a frog under the 
lens of a powerful Microscope,” a writer in the ‘ Times ’ * points out the 
indubitable claim of Harvey ; at the same time he acknowledges that 
one link in the chain was wanting. 
“ Harvey knew that the blood found some channel by which it passed 
from the terminations of the arteries into the commencement of the veins, 
but he could not discover what that channel was. He conjectured that 
the blood percolated through the tissues, like water through earth ; and 
at that time there was no Microscope in existence capable of showing 
either a capillary vessel or a stream of blood-corpuscles. Harvey’s 
discovery was completed by Leeuwenhoek, in the second half of the 
century, by the aid of a Microscope which he made for himself in 1654, 
and which rendered visible, for the first time, the vessels and the blood- 
corpuscles in the web of a frog’s foot. Canon Wilberforce is therefore 
entirely wrong in his statement of what he calls a fact ; and, if his fact 
were as he puts it, he would still be entirely wrong in his inference. 
If Harvey himself had seen a blood-stream in a capillary vessel, the 
sight would not have taught him the course of the circulation. The 
way in which blood passes from an artery to a vein through a capillary 
does not throw any light upon the nature and direction of its general 
circuits — first through the body, and secondly through the lungs, nor 
upon the function of the heart, by which it is propelled. The Micro- 
scope placed the keystone upon the arch of Harvey’s discovery, but it 
could never have enabled him to construct the arch itself.” 
Twentieth Annual Report of Chief of the Division of Microscopy, 
U.S.A.j — Mr. T. Taylor reports: — “ The work done during the past year 
relates in a great measure to the microscopical investigation of food 
adulterations, food-fats and oils, textile fibres, and edible and poisonous 
mushrooms. In relation to fibre investigation, I have had constructed, 
with your permission, a new machine of my invention for determining 
* Oct. 29th, 1892. f Report of the Microscopist for 1891, pp. 405-6. 
