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Iris Diaphragm proving the circular form whether expanding 
or contracting. By J. II. Brown, Esq. 
Although my new form of diaphragm is at first sight 
somewhat complex, it is in reality extremely simple. A 
glance at the diaphragm will give a better idea of its con- 
struction than any amount of written description. It essen- 
tially consists of a number of triangular blades (a), each fur- 
nished with two axes, one of which works in a hole in the 
plate (b) . The blades expand or contract the aperture of the 
diaphragm by giving a rotatory movement to either of the 
brass plates, whilst the other remains stationary. The blades 
being thus moved simultaneously, and their edges “next 
the aperture curved, they form an opening very nearly 
circular. 
The first diaphragm I made of this pattern contained six- 
teen blades, but I find twelve or even less are sufficient. 
