PROCEEDINGS OF SOCIETIES, 
Mepicat Microscopical Soctrery. 
16th October, 1874. 
New and expeditious method of Micrometry. By John Gorham, 
Esq.—The principle of the instrument described depended upon 
the measurement of lines drawn parallel to the base of an isosceles 
triangle—the base of the latter being given—by means of the sides, 
which are divided into a known number of parts. The triangle 
is obtained by dividing through the centre a disk of brass, about 
1; in. in diameter and half an inch thick, and bevelled at the 
edge so as to allow of its being embraced by a stout india-rubber 
ring, by which means the two portions are held in perfect appo- 
sition at the edges of the section. The line of section for the 
distance of one inch from the circumference is marked out into 
fractions of an inch, at least into thirty-two parts, a less number 
being insufficient to obtain a minute result. A piece of paper of 
known thickness is now inserted between the halves of the disc 
and moved along till its edge touches the commencement of the 
marked inch, the elastic band retaining it in its place, and thus 
an isosceles triangle or gap is left with a base the thickness of 
the slip of paper, and with an edge of one inch divided, as stated, 
into thirty-two equal parts, If a hair or cobweb be passed along 
the slit from base to apex it will be arrested somewhere, and by 
reading off the number opposite which it stops—a simple matter 
of multiplication, the base of the triangle bemg known—will 
give the diameter required. For microscopic purposes the instru- 
ment is placed on the stage, and the object to be measured, placed 
on a thin glass cover, is slid over the aperture till it exactly at 
one point spans it ; the diameter is then read off. To obtain still 
greater accuracy Mr. Browning has added a screw of known 
value to separate the halves of the micrometer in lieu of the slip 
of paper. 
In answer to some questions by members of the Society, the 
President replied that the instrument was specially designed for 
unmounted objects, the thickness of an ordinary glass slide being 
rather an objection in the case of mounted ones; a thin glass 
cover might be in all cases employed for placing the specimen, e.g. 
blood or pus, upon. 
