596 THILOSOPHICAL TRANSACTIONS. [aNNO I7Q5. 



The two outside divisions of tlie ladders serve for mounting into the gallery, 

 and therefore contain rounds as well as flats. The distance of the sides, the flat 

 parts of which, as in common ladders, are put facing each other, is 18 inches, 

 and remains the same up to the end. But the two inside divisions, which have 

 no rounds, are placed with the flat face outwards, and the distance between these 

 faces being 2 feet 8 inches up to the top, the parallelism of these divisions is pre- 

 served outside, while that of the mounting ladders is continued within. The 

 reason of this arrangement is, that the brackets which support the moveable 

 gallery rest on the inside frames of the ladders. These go upon 24 rollers, 12 of 

 them confining the galltry sideways, while the other 12 support it, the paral- 

 lelism was of course required where it is placed. The mounting ladders are made 

 parallel within, that a moveable chair, intended to he 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 difl'erence 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 

 timber might be firm and strong ; and 2dly, 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. The last flat was put into the ladders after they had been erected and 

 secured together. 



The middle top cross-beam is placed above the two sets of ladders in the angle 

 made by their crossing each other. The method of keeping it there, and secur- 

 ing the proper distance of the ladders by this beam, which is of a cylindrical form, 

 is as follows : 12 iron loops, shaped to the ends of tlie ladders, with arms to 

 them like lamp-irons, and a hole at the end of each arm, are slipped down on 

 the ends of the ladders, till 2 and 2 of them meet in the middle of the cross-beam, 

 which is about 8 inches in diameter. Here a screw bolt, coming up through 

 the beam, passes into the holes of the 2 irons, where all is screwed firmly to- 

 gether. By this means no holes are made to weaken the tapering ends of the 

 ladders, and the centre beam takes firmly hold of every one of them ; so that 

 were even the pins pulled out, the ladders would still remain firmly kept to- 

 gether. When the ladders had been properly adjusted to their places, they were 

 supported immediately by 2 capital side braces. These consist ot 2 whole masts, 

 of nearly the same dimensions with those which were sawed through for making 

 the ladders: the upper end of each was mounted with an iron loop, 2 claws, and 

 a ring, which were put on with bolts. The poles being drawn up, the loops 



