no 
In order to facilitate observations of this character, and to 
enable the observer to dispense with an assistant, I have 
recently adapted to my telescope (of 5in. aperture) an 
apparatus which may be termed the “ Iris Diaphragm,” as 
its action resembles to some extent the expansion and con- 
traction of the pupil of the eye. The invention was, I 
believe, patented by Mr. Jennings, of London, as a capsule 
for closing jars, bottles, &c., but has been superseded by a 
more simple method for the same object. If found to be 
practically successful for the purpose I have now applied it 
to, it will, I think, be extremely useful in the Observatory, 
and form a desideratum long required by Astronomers. A 
great saving of time will be effected, and the results will be 
regarded with greater confidence. 
The following is a description of the invention, and the 
method I propose for adapting it for astronomical purposes. 
The invention consists of two rings of metal, one working 
within the other, of nearly the same diameter, but differing 
in width, to the outer edges of which, is attached a piece of 
sheet india-rubber joined at the ends, and so placed that 
when the rings are moved in opposite directions the india- 
rubber is stretched, and closes the aperture of the rings when 
they have made about one half of a revolution, the aperture 
remaining circular or nearly so, its perfect circularity 
depending on the proper attachment of the india-rubber. 
The adaptation I have effected in the following manner. 
A flat ring of tin with a flange is made to fit accurately the end 
of the dew-cap of the telescope. To the flange the diaphragm 
is soldered; to the broader ring of the diaphragm is fixed a 
circle of brass, having teeth cut rather more than one-half 
round its circumference. Fixed to the ring, which is attached 
to the dew-cap, is a bearing for a small pinion, which gives 
motion to the half wheel by means of a slender rod (of brass 
tubing) the length of the telescope, having at the eye-piece 
end, a handle of convenient form, and worked by the left 
