THE MIcRoscope. 267 
The two supports are much more preferable, and in the end it 
might be to the optician’s advantage to add them to all his 
stands. The extra cost could not be great. 
In Messrs. Bausch and Lomb’s list the cheapest and the most 
costly stands have double pillars, while the intermediate grades 
have but one. All of Mr. Gundlach’s have the single pillar. 
All of Mr. Bulloch’s designs, with one exception, have two. 
Messrs. J. W. Queen «& Co.’s cheapest, even their cheapest 
“Acme,” have two, while their more costly stands have one. Mr- 
Zentmayer’s least and most expensive have two, while his inter- 
mediate has but one. The preference seems to be personal 
with the manufacturers, as it is with the writer ; otherwise I am at 
a loss to understand the diversity to be noted m the foregoing list. 
The origin of the double pillars is sufficiently curious to be 
mentioned. The improvement, which was made forty years ago 
or more, by George Jackson to whom we owe several important 
suggestions, is due to the fact that in one respect Jackson was not 
an accomplished workman, for he could not file well. Up to his 
time only a single pillar had been used, with a joint at the top, 
but Jackson wishing to made himself a stand, failed to procure 
acceptable results by filing out the parts of the joint, the only 
method of doing it, as plaining machines were then unknown. 
It therefore occurred to him that he might turn a horizontal 
axis, and support each end at the top of an upright pillar, which 
he did. The idea was adopted by several London manufactur- 
ers, and is now used for what the writer, at least, considers the 
most desirable stands. 
The metal of the pillars may be either iron or brass, like the 
foot, the choice depending on the expense to be incurred. 
Another method of suspending the instrument, an American 
device and adopted, so far as I know, by only two of our manu- 
facturers and imitated by one in England, consists in making 
the arm a segment of a circle whose centre of curvature is at the 
centre of the stage. It has a groove on each side into which fit 
two tongues gliding in the grooves when the instrument is in- 
clined, the friction being great enough to hold it at any point. 
If it becomes necessary to retain the arm more firmly in posi- 
tion, a tightening screw is provided. This is the “American Con- 
centric Microscope,” made by Messrs. Bausch and Lomb at the 
suggestion of the Hon. J. D. Cox. 
