VOL. LXXXV.J PHILOSOPHICAL TRANSACTIONS. 597 



were put on the centre pins, and keyed on ; while the lower ends of the poles 

 were lifted into their places, on the cross foundation, and fitted on the elliptical 

 marks at the ends of them. 



After describing some other ladders and braces, it is then added, besides these 

 there are 3 sets of braces, which serve to confine the poles to their stations. The 

 highest set meets the side brace at the 15th flat. The next meets the middle 

 brace at the 10th fiat, and both these make with the side braces a triangle, in the 

 vertex of which is inclosed the large pole that is braced by them. At the 5th fiat 

 a 3d set of braces, which incloses the two small poles as well as the large one, is 

 carried round with 4 divisions. The front of the ladders, it is very evident, would ■ 

 admit of no brace, and is left entirely open for the tube of the telescope to range 

 in. It receives however some confinement from the moveable gallery, which is 

 always hung across the front, in the place where observations are to be made. 

 This gallery consists of 3 separate parts : 2 double side brackets with a small plat- 

 form on them, and a middle passage. The whole of it when joined together is 

 properly railed in at the front by wooden palisades ; and on the inside by light 

 iron-capped bars. Each of the brackets by which the gallery is supported con- 

 sists of 3 frames; a parallelogram for the bottom, with 2 triangular sides erected 

 on the former, and held together by a narrow platform on the top. On the plat- 

 form are fixed palisades, which turn the corner at the front, and are continued 

 so as to meet the middle platform of the gallery. The palisades are strengthened 

 and rendered steady, by a seat which is fastened against them, and supported 

 from the floor by slight iron bars. 



There is a small stair-case by which we may ascend into the gallery, without 

 being obliged to go up any ladder ; and as that is strong enough to hold a com- 

 pany of several persons, and can afterwards be drawn up to any altitude, observa- 

 tions may be made with great conveniency : the activity of an astronomer how- 

 ever will seldom require this indulgence. The readiness with which I ascend the 

 ladders, has even prevented my executing the projected running chair, which may 

 easily be added, to take a single person into the gallery after it has been already 

 drawn up to its destined situation. A view of the stair-case in the fig. will suflice 

 to point out its construction. I ought only to observe, that in the engraving the 

 gallery is placed higher than where it will join the stair-case properly, but that 

 when it is lowered on purpose, it becomes then to be just one step above the little 

 landing-place of the stair-case, and the palisades of the former unite with the 

 railing of the latter. 



The next piece to be described, is the tube of the telescope. This, though 

 very simple in its form, which is cylindrical, was attended with great difficulties 

 in its construction. No one will wonder at this who considers the size of 

 the tube, and the materials of which it is made. Its length is 3Q feet 4 inches ; 



