TRANSACTIONS OF SECTION G. 1189 
bridge are necessarily built up of numerous steel plates, the size of each bed-plate 
being 37 ft. long by 17 ft. 6in, wide. To grip together the 47 separate sates 
into a solid mass 3,800 rivets 1} in. in diameter with countersunk heads on both 
sides are required, and, remembering that the least dimension of the bed-plate is 
17 ft. Gin., it will be seen the ordinary ‘gap’-riveter would not be applicable. 
A special machine was therefore designed by Mr. Arrol, consisting of a pair of 
irders and a pair of rams, between which the bed-plate to be riveted together 
4. A double ram machine had for like reasons to be devised for riveting up 
the great tubular strute of the bridge. 
ot merely in the superstructure, but in the construction of the foundations, 
were hydraulic appliances of a novel character indispensable at the Forth bridge. 
Huge wrought-iron caissons or cylinders, 70 ft. diameter and 72 ft. high, were 
taken up and set down as readily as a man would handle a bucket. In sinking 
these caissons through the mud and clay of the Forth compressed air was used. 
When the boulder clay was reached the labour of excavating the extremely hard 
and tenacious materia) in the compressed air-chamber proved too exhausting, 
ickaxes were of little avail, and the Italian labourers who were chiefly employed 
lost heart over the job altogether. But a giant power was at hand, and only 
required tools fit for the work. Spades with hydraulic rams in the hollow handles 
were made, and, with the roof of the compressed air-chamber to thrust against, 
‘the workmen had merely to hold the handle vertically, turn a little tap, and down 
went the spade with a force of three tons into the hitherto impracticable clay as — 
sweetly as a knife into butter. Probably, when addressing you thirty years ago, 
Sir William Armstrong never anticipated that a number of hydraulic spades would 
be digging away in an electrically lighted chamber or diving bell, 70 ft. diameter 
and 7 ft, high, 90 ft. below the waves of the sea; but still the spades come strictly 
within the definition of the class of machines, intermittent in their action and 
extending over a large area, which it was his aim to introduce. It would be 
possible, indeed, with the appliances at the Forth bridge, to arrange that the simple 
ing of a valve should start digging at the bottom of the sea, riveting at a 
height of nearly 400 ft. above the sea, and all the multifarious operations of bend- 
ing, forging; and hoisting, extending over a site a mile and a half in length. 
It would not only be impossible to build a Forth bridge, but it would be 
equally impossible to fight a modern ironclad without the aid of hydraulic 
al Most of the Presidents of this Section have referred in the course of 
their addresses to our Navy, and certainly the subject is a tempting one, for the 
rogress of mechanical science in recent years ooald not be better illustrated than 
a description of the innumerable appliances which go to the making and work- 
‘ing of a modern ironclad. Let me quote a single passage from a pamphlet by a 
_ naval officer, which caused a great stir a few years before the Crimean war, that I 
may recall to your minds what was the speed and what the armament of our fleet 
at that comparatively recent period. ‘Conceive,’ said Captain Plunkett, R.N., ‘a 
British and French fleet issuing simultaneously from Spithead and Cherbourg; 
_ seven hours’ steaming at the rate of six miles an hour will bring them together. 
_ Asingle glance at the heavy and well-appointed tiers of a line-of-battle ship’s guns 
will satisfy anyone that they are no toys to be placed in the hande of novices. 
Formidable batteries of the heaviest ordnance are there—not a gun under a 
$2-pounder, and many 68-pounder shell guns.’ In little more than a quarter of a 
century engineers have changed all that, and advanced to 20-knot vessels and 120- 
ton guns. Archwologists tell us that our predecessors in mechanical science, of 
_ the Stone Age, were apparently a thousand or more years in finding out that the 
_ best way of fitting an axe was to slip the handle through the axe and not the axe 
through the handle. Engineers of the present day may be excused, therefore, for 
occasionally illustrating the rapidity of the advance of their science by contrasting 
the ships of thirty years ago with our modern ironclads. 
The latest type of battle-ship weighs, fully equipped, about 10,000 tons. There 
are about 3,400 tons of steel in her hull, apart from armour, which with its backing 
will weigh a further 2,800 tons. The machinery, largely of steel, is about 1,400 
tons; the armament, including ammunition, 1,100 tons; the coals, 1,100 tons; and 
