35 ® Dr. Herschei/s Description of a 
The reason of this arrangement is, that the brackets which 
support the moveable gallery rest upon the inside frames of 
the ladders. These go upon 24 rollers, as will be seen here- 
after, and 12 of them confining the gallery sideways, while the 
other 12 support it, the parallelism was of course required 
where it is placed. The mounting ladders are made parallel 
within, that a moveable chair, intended to be made if required, 
might be drawn up with a person seated in it, to prevent the 
fatigue of mounting, or take up in safety any one who chanced 
to be afraid of ascending an open ladder. 
The back set is constructed like the front ; and, the ladders 
being of the same length, the only difference is that no rounds 
have been put into them. The flats have been preserved on a 
double account ; first, that the connection of all the side tim- 
ber might be firm and strong ; and secondly, that every part of 
the frame might be accessible. For by means of these flats we 
have steps of 27 inches, which may be ascended with tolerable 
ease, when occasion requires. 
The method of joining the front and back at the top, is by 
passing one set of ladders through the other so as to embrace 
it ; the backs, therefore, which go outside, are placed a little 
farther asunder than the fronts ; and the same pins pass 
through them both, at q k and 9 1, where a section of the back 
ladders is shewn, with the pins going through them. The last 
flat was put into the ladders after they had been erected and 
secured together. 
The method of setting up and bracing the ladders was as 
follows : 
When the eight principal beams of the groundwork ABC 
D E H I K, fig. 3. had been put together, the eastern front 
