[43] From Mr. Clegg’s specification--the same letters of reference indicate the same parts in all the designs.
For this purpose the top or ridge joints which unite the two sides of the gas holder, are slightly raised up when the sides close or approach together, or slightly depressed when the sides open out or recede from each other. To guide the whole gas holder in this movement, two perpendicular rods rise from the bottom of the shallow tank which pass through sockets in the ridge joints at the upper part of the gas holder. These sockets are secured by collars of leather round the shafts or rods, to prevent the escape of the gas, and they are braced by chains proceeding from their upper extremities and fastened at the ground on each side of the tank.
The weight of the gas holder is balanced by levers bent in the form of the letter L, and placed inside of the gas holder. These levers move on centre pins fixed at the bottom of the shallow trough, which pass through the angles of the L levers. The perpendicular arms of the levers are jointed at their upper extremities to the sides of the gas holder, nearly in the middle. At the ends of the horizontal arms of the L levers, are weights to counterbalance the weights of the gas holder, and both sides of the gasholder are provided with these kind of levers, which at the same time that they balance its weight cause the ridge joint of the machine to rise and fall, as before described, so that the under edges of the gasholder, which are immersed in the water to confine the gas, must move in an horizontal plane instead of describing an arc of a circle as they would do if the ridge joint was a fixed centre of motion.
When the gas holder is closed the perpendicular arms of the levers stand nearly in a perpendicular position, but when the gas holder is opened out the levers become inclined. And as they move upon a fixed fulcrum at their lower extremities, and are jointed to the sides of the gas holder at their upper extremities, they allow the whole of the gas holder to descend gradually upon the guide rods, nearly in the same degree as the lower edges would rise up if the ridge joint was stable, and if the sides described an arc of a circle.