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POPULAR SCIENCE REVIEW. 
brought before the society the most important improvement in the micro- 
scope since the days of Mr. Wenham. — Mr. Browning briefly explained his 
reasons for believing that the second prism used did not produce imperfect 
definition. — The President said that he would confirm Mr. Lee’s observations 
concerning the use of high powers in Mr. Stephenson’s microscope. The 
T \th had been used with great advantage, and though both the fields of 
view were not equally illuminated under this high power, it would at once 
be seen from the construction of the instrument that only the art of the 
optician was required to make both tubes equally valuable in using high 
powers. Those who had had the pleasure of examining the instrument as 
well as himself would bear him out in the statement that the effect of 
giving an erect image is of the highest importance in cases where dissection 
was being conducted. The instrument devised by Mr. Stephenson contained 
no error of importance, and the slight want of flatness in the field could be 
readily obviated. 
Hippunc Acid as a Microscopic Object. — In the Journal of the Quekett 
Club for April, Mr. T. Charters White gives an excellent account of the 
crystallization of this substance in order to prepare it for the microscope. 
The Comparative Steadiness o f the Ross and Jackson Plan of Microscope . — 
An important practical paper was lately read before the Royal Microscopical 
Society by Dr. Carpenter, giving the results of his observations on the relative 
steadiness of these two forms of microscope stands. Speaking of his expe- 
rience of the two models in the last deep-sea expedition, he said : “ When 
the ship was going under 1 easy steam,’ with either a fair wind or a light 
contrary breeze, there was enough gerieral vibration to produce a considerable 
differential vibration in any microscope liable to it, and thus to occasion a 
decided tremor in the image even when only moderate powers were em- 
ployed. But when we were steaming with full power against a head-sea, 
the general vibration became so great as to be the severest test of the me- 
chanical arrangements of our microscopes. Now, it happened that whilst 
my own instrument — a portable binocular microscope weighing less than 
seven pounds , which is my usual travelling companion — is constructed on the 
Jackson model, Professor Wyville Thomson was provided with an instru- 
ment of about the same scale, but heavier by some pounds, made upon the 
Ross model ; and we thus had an opportunity of fairly testing the two plans 
of construction under circumstances peculiarly critical. The difference in 
their performance was even more remarkable than I had anticipated. I 
found that I could use a ith-inch objective on my own microscope, with 
an even greater freedom from tremor in the image than I could use a frds- 
inch objective on Professor Wyville Thomson’s. In fact the image ‘ danced’ 
very perceptibly in the latter, even when the l|-inch objective was in use.” 
— Monthly Microscopical Journal , April. 
An American Graduating Diaphragm. — Mr. Zentmayer has described an 
instrument of this kind in the Journal of the Franklin Institute (February. See 
also Monthly Microscopical Joumal f June). It has been described also in the 
Chemical Sews by Mr. Henry Morton. It consists of two cylinders or rollers 
with parallel axes and surfaces in contact, having similar conical grooves on 
their surfaces, and fine teeth cut at one end of each, which, gearing together, 
cause them to rotate in unison. There is, theoretically, an objection to a dia- 
