Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/316

298 298 X&amp;gt; I Y I N G Fia. 7. Diver s Helmet. with a corresponding screw, can be attached or removed by one eighth of a turn. The helmet, a side view of which is given in fig. 7, is made of tinned copper, and fitted in front with three strong plate-glass win- dows, or bulls eyes, in brass frames protected with guards. Messrs Heinke introduced slid ing covers to draw over these win dows in case of their getting bro ken. The front eye piece is made so that it can be unscrewed, and in this way the diver on ascend ing can rest him self for a short time or give orders without removing the rest of his dress. Messrs Barnett have introduced instead of this a hinged glazed frame, which fits tightly into a conical vulcanized india-rubber seat like tlio ordinary port hole of a ship, so that it can be opened by the diver himself the moment his head is above water, and being attached to the helmet it cannot be dropped acciden tally into the sea or otherwise mislaid. An outlet valve a is fixed at the back of the helmet, which, opening outwards, permits the escape of the foul air but prevents the entrance of water. The inlet valve b to which the hose is attached is also fixed at the back of the helmet, and is so constructed as freely to admit the air from the force pump ; but should anything occur to the hose or pumps the valve at once shuts, inclosing a sufficient supply of air in the dress to support the diver till he can be hauled to the surface. The air after entering by the inlet valve is conducted in tubes c to the front of the helmet, so that the diver has the advantage of inhaling fresh air, and the front glasses are kept free from the condensation of his breath which would otherwise take place. On each side of the helmet is a hook over which the cords pass which carry the front and back weights, and a brass stud to one of which the life line, and to the other the air tube, are attached ; dd is the joint by which the helmet is screwed upon the breast-plate. The back and front weights weigh about 40 Ib each, and are held close to the diver s body by means of a lashing passing under his arm-pits. The boots are made of stout leather, with leaden soles, secured by two buckles and straps, each boot weighing about 20 Ib. The cost of a diving dress, with all its appliances, is about 140. The sponge, pearl, and coral fisheries, originally carried on only by naked divers, as already noticed, are now con ducted to a great extent by the help of artificial aids ; and, according to Mr Siebe, upwards of 300 sets of diving dresses are employed in the. Mediterranean sponge fisheries alone, and they are being introduced in the Bahamas, Bermudas, Ceylon, the West Indian Islands, and on the coast of Australia. As already stated, at moderate depths not exceeding 30 to 40 feet, and with clear water, sufficient light is transm i tte d to enable the diver to perform any ordinary work, and in working in turbid water with the diving bell candles are employed. Mr Siebe has also constructed an electric lamp and an oil lamp which can be employed where light requires to be used by divers at great depths. Captain Eads 1 states that at the Mississippi bridge candles were at first employed, which, under a pressure of 100 feefc, were found to be burnt down in about three-fifths of the time required in the open air; under a pressure of 80 feet it was found that a candle if blown out by the breath would immediately reignite ; and at the depth of 108^ feet a candle was blown out thirteen consecutive times in the course of half a minute, and each time excepting the last was reiguited. The depth at which diving can be safely conducted is a question of importance. The ordinary depth at which the diving bell has been employed in harbour works is from 30 to 35 feet, and it has been used in GO feet at Dover. With the diving dress much greater depths have been attained. Mr Siebe relates that in. removing the cargo of the ship &quot; Cape Horn,&quot; wrecked off the coast of South America, a diver named Hooper made 7 descents to a depth of 201 feet, and at one time remained 42 minutes, sup posed to be the greatest diving feat ever achieved. M. Frendenberg states that in the repair of a pump in the Scharley zinc mines in Silesia two divers went down the pump well to a depth of 85 feet, remaining from periods varying from 15 minutes to two hours. 3 In the knowledge of the author the greatest depth at which the diving dress was used in the open sea was in the Firth of Forth. A Royal Commission &quot; on the Operation of the Acts relating to the Trawling for Herring on the Coast of Scotland &quot; resolved to obtain the herring spawn from various portions of the exposed parts of the firth, and this duty was successfully accomplished in depths of from 14 to 16 fathoms, from the deck of the &quot; Princess Royal &quot; cutter, under the command of Mr Macdonald. The writer is indebted to Mr P. J. Messent, the engineer Divin of the Tyne piers, for the following notes of his experience work at that work. &quot; On the Tyne Pier works helmet and bell divers are employed simultaneously the former for excavat ing for and fixing the feet of the piles of which the staging is formed, the bell divers for levelling the foundations and fixing the blocks of which the pier is composed. Tho helmet diver has greatest power in lifting. He can exert but a few pounds of force in pulling downwards (unless he can fasten himself down) on account of his buoyancy, and for the same reason he cannot pull or push horizontally with much force unless he has a fulcrum or stop for his feet or body. Thus, in boring au augur hole in a pile he would have to lash himself to it, unless there was a pro jecting rock or stone that he could get his foot against. In the use of a hammer and other tools for striking he is restricted by the water,&quot; but Mr Messent has known good men do fair work with a hammer and chisel. It is difficult for them to walk against even a moderate tide, and men who by accident get on the (lee) tide side of their work, generally have to be hauled up to their boat and lowered down again in order to get on the (windward) tideward side of it ; again experience enables many of theso difficulties to be met or modified, but it is advantageous to bear them in rnind in arranging work for divers. Most of the divers at the Tyne have been made or instructed on tho works, and of the men who have tried helmet diving not more than one out of three or four succeed or become divers, the failure being sometimes from physical causes, but more often from want o/ head. There is less difficulty in making bell-divers, probably on account of their work ing in company, there being always two men in a bell, and the same amount of self-reliance is not needed. 1 Reports by Captain James B. Eads to the President and Directors of the Illinois and St Louis Bridge Company. 2 Minutes o/ Proceedings o/ Inst. oj Civil Engineers, vol. xlv. p. 343.