TRANSACTIONS OF THE SECTIONS. 9 
Having no stands of his own, except the Herschel stand, (and this certainly defec- 
tive in stability, in consequence of the great mirror being unsupported except by the 
tube, upon which it acts through a long and powerful lever of agitation,) Dr. Greene 
turned his attention to the construction of some simple stand based upon the principle 
of stability which the triangle affords, and presented a model of his first attempt to 
attain that object. 
In this arrangement the heel of the telescope hangs by two pivots upon two Ys 
fixed to the upper surface of a flat circular disc, which revolves upon another similar 
disc, by means of a pin in the centre; the lower disc stands upon three very low feet to 
ensure its stability. The upper or eye-end of the telescope is attached by a pin to an 
equatorial slide. ‘The pin is united to a slide which moves parallel to the tube of the 
telescope at its under side, and being moved by a rack and pinion, gives the slow 
elevation movement. The equatorial slide is supported by a pair of shears, capable 
of being lengthened or shortened at pleasure, to effect the quick motion in altitude. 
The legs of the shears rest upon the two extremities of a sliding piece moving by rack 
and pinion in the groove of a piece of mahogany or other hard wocd in the shape of 
the letter T, supported by three very low feet to ensure its steadiness. The sliding 
piece is moved by a long handle attached to the pinion, and gives the slow azimuth 
motion to the entire stand. To unite the different parts into one system, the piece 
which supports the shears, and the lower circular disc which supports the heel of the 
telescope, are attached by two bars with hooks at each extremity, the bars being 
themselves bound together by two diagonal braces. 
It will be seen at a glance, that the telescope and its stand form one great triangle, 
while each of its parts is a minor triangle; that the great mirror is solidly supported, 
having no tendency to disturb any part of the fabric by its disposition to be moved by 
any slight external force. 
On an easy Method of contracting the Aperture of a Large Telescope. 
By Henry Lawson, .RS., FRAS., &e. 
It is well known to the practical astronomer, that in using a telescope of large 
diameter it is needful to contract the aperture of the object-glass when measuring 
binary stars, &c., and also when the haziness of the atmosphere demands such con- 
traction. The mode adopted is the adaptation of a brass tube, 6 to 12 inches long, to 
the eye-end of the telescope tube, in such a manner that it may slide out and in with 
facility. Into one end of this tube the eye-pieces of the telescope must screw (or 
what is better, slide). Within this tube is to be placed a moveable diaphragm, made 
to slide up and down the tube by means of a slit and stud. The diaphragm is to be 
pierced with an aperture of such size as just to let the whole cone of rays proceeding 
from the object-glass pass through it towards the eye-glasses, when the diaphragm is 
drawn down or stands near to the eye-piece. When the aperture of the object-glass is 
required to be contracted, the diaphragm must be slid towards the object-glass, and it 
wiil have the effect of circumscribing the cone of rays to any required diameter. The 
benefits resulting from the above-described plan are the following: that the astro- 
nomer can with the greatest facility and without moving from the eye-end of his tele- 
scope, adjust or contract the aperture of the object-glass to any required diameter ; 
he can vary the magnifying power without shifting or deranging the aperture; and, 
lastly, he can produce these benefits without fear of altering the adjustments, or 
turning the telescope from the object in view. 
On the Arrangement of a Solar Eye-piece. 
By Heyry Lawson, F.RS., F.R.AS., &c. 
This arrangement does away with the inconvenient and dangerous breaking of the 
dark glass when viewing the sun through telescopes of large size, and enables the 
astronomer to view the sun with the whole aperture of his telescope, however large it 
may be; thus giving an immense advantage when scrutinizing the wonderful and 
most interesting appearances of the solar disc. The method consists in placing the 
dark-glass or glasses within the telescope, by means of a brass tube supported between 
the object-glass and the eye-glass of the telescope, the tube being from 3 to 18 inches 
(according to the length of the telescope), measured from the eye-piece, to which 
