5Q8 PHILOSOPHICAL TRANSACTIONS. [aNNO IaQo. 



it measures 4 feet 10 inches in diameter, and every part of it is of iron. On a 

 moderate computation, the weight of a wooden tube must have exceeded an 

 iron one at least 3000 lb. ; and its durability would have been far inferior to this 

 of iron. The body of the tube is made of rolled, or sheet iron, which has been 

 joined together without rivets ; by a kind of seaming, well known to those who 

 make iron funnels for stoves. The whole outside was thus put together in all its 

 length and breadth, so as to make one sheet of nearly 40 feet long, and 15 feet 

 4 inches broad. The tools, forms, and machines, we were obliged to make for the 

 construction of the tube were very numerous. For instance, inthe formationof this 

 large sheet, a kind of table was built for its support, which grew in size as 

 the sheet advanced, till when finished, it was as large as the whole of it. In 

 the formation of the sheet, cramping irons, seaming bars, setting tools, and 

 claw-screws, were made in great number, to confine and stretch the parts as 

 they were seamed together. The small single sheets of which this large one is 

 composed, are 3 feet 10 inches long, and about 23^ inches broad. Their thick- 

 ness is less than the 36th part of an inch; or, what will be a more precise 

 measure, a square foot of it weighs about 14 oz. They are joined so, that the 

 middle of a whole one always butts against the seam of the preceding 2, in the 

 manner of brick-work, where joints are crossed by bricks above and below. 



When the whole sheet was formed, which was done in a convenient barn not 

 far from my house, the sides were cut perfectly parallel, and afterwards bent 

 over at the ends in contrary directions, to be ready to receive each other. A 

 number of broad hooks, such as were proper for grasping the sides of the sheet, 

 with loops at the other end for cords to go through, were now prepared with 

 their necessary tackle. 12 pulleys were fastened about 1] feet high, on move- 

 able beams, that might be drawn together; 6 on each side. The sheet was now 

 taken up, by occasioning all the corded hooks to be drawn at the same time, 

 and while it was kept suspended our large table was taken to pieces. Another 

 kind of support was now put under the middle of the sheet to receive it. The 

 form of this was that of a hollow segment, or quarter of a cylinder, cut length- 

 ways, to the extent of a few feet more than the length of the intended tube; 

 and the concavity of which was formed by the same radius as that of the tube. 



The sheet being let down, it rested on the hollow gutter; for so we may call 

 the machine that was placed under it. Six moveable segments of a whole 

 cylinder, or circular arches, about 3 feet wide each, which had been prepared, 

 were now brouglit on the sheet, and placed at proper distances from each other. 

 By these the sheet was pressed down on the foundation, so that no injury could 

 be done by walking on it. The beams which held the pulleys were now brought 

 close togetlier; which being done, we hung the pulleys of one on the hooks of 

 the other beam, so as by tiiat means to cross the cords which held the sheet. 



