3 64 Dr. Herschei/s Description of a 
The hooks sink down into the floor of the sides so as to be 
level with the surface ; and go over the inside of the support- 
ing triangles, fig. 18. ; which, for the sake of additional 
strength, and to prevent their being galled by friction, are 
lined with an iron plate at the inside, in all their length. 
The light iron rail joining the bars of the inside, which are 
along the margin l aeg b a, fig. 19. are left moveable at the 
bottom, in the places l a and m b ; where they run down into 
loops ; by which means they admit of being a little displaced. 
The contrivance to make the junction of the front and side 
palisades moveable is by means of a front bar. This being 
slipped upon pins at the end of the rails belonging to the sides, 
a hole at each end of the bar, lined with an iron plate about 2 
inches long, through which the pins pass, permits the bar to 
be drawn either way. There are moreover at the ends of the 
rails, which are fixed to the platform, two iron hooks ; which, 
though they bind the rails to the front bar, still permit it to go 
up or down a little way, as occasion may require. By this 
means a deviation from the level, amounting to six or eight 
inches, will occasion no injury to the wood-work. The greatest 
security against such a derangement of the platform, however, 
will be explained hereafter, when we come to the mechanism 
by which it is moved. 
There is a small staircase 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 company of several persons, 
and can afterwards be drawn up to any altitude, observations 
may be made with great conveniency : the activity of an as- 
tronomer, however, will seldom require this indulgence. The 
readiness with which I ascend the ladders, has even prevented 
