Monthly Microscopical 
( 170 ) [ Journal, Sept. 1, 1870. 
NOTES AND MEMORANDA. 
Continuously Adjustable Diaphragm.—Mr. J. Zentmayer, of Phi- 
ladelphia, U.S., some time since devised and constructed a diaphragm, 
of which the accompanying woodcuts are views in two conditions of 
adjustment. 
Two cylinders or rollers of equal size and parallel axes are so 
mounted as to be revolved in contact by fine gearing at one end. 
Similar conical grooves are arranged in the surfaces of these in such a 
manner that they produce together a circular opening, which will of 
course vary its size according to the position of the cylinders in their 
revolution. There is theoretically an objection to a diaphragm of this 
construction, from the fact that its opening will not be always in the 
same plane. With the largest opening, the smallest section at right 
angles to the line of sight will be nearest to the plane passing through 
the axes of the cylinders, and with the smallest opening it will be 
farthest from this plane. This difference is, however, very small in 
fact, and might in certain cases become advantageous. 
