March 13, 1885.] 



♦ KNOWLEDGE ♦ 



217 



Mr. Fletcher, in increasing this grand collection since 

 about the year 1S60. Mention may also be made of 

 the great increase of specimens in the fine collection in 

 Paris, under Prof. Daubret>, as well as that of Vienna, 

 formerly under Professors Haidinger and Tsohermnk, and 

 now under Dr. Brezina. These three collections are with- 

 out doubt the tinest and most valuable in tho world. Many 

 cities in Europe, as well as several of those in the United 

 States, also possess remarkably fine and valuable collections. 



Persons frequently ask the questioti, Aro not people 

 sometimes killed by these falls of meteorites 1 We can 

 only answer, that there are instances recorded of jiersons 

 being killed, among others by a large full in Africa ; 

 it is noted by Chladni, one of the earliest of modem 

 writers on this subject, that about the year 1020 many 

 persons and animals were killed ; and, again, in tho year 

 1511, about five o'clock one evening, when a priest was 

 struck and killed on the spot ; still later, in 1050, a monk 

 was killed by a meteoric stone ; these seem to be all the 

 instances recorded of loss of life. 



^lany persons not having a knowledge of these objects 

 have an erroneous idea that the globular form of tho 

 marcasite variety of iron pyrites, which are extremely 

 common in chalk districts, especially in the south of Eng- 

 land, are meteorites, or aerolites — or thunderbolts as they 

 term them. This mineral is of a brass j-ellow colour when 

 fresh out of the chalk, but being very liable to decompo- 

 sition, generally appears brown ; but when broken, the 

 brass coloured radiating structure appears. 



Any one interested in this subject of meteorites would 

 do well to procure the printed cata'ogue of the British 

 Museum collection of meteorites, which has a brief intro- 

 duction to the subject. The Paris collection has also a 

 valuable descriptive catalogue, and we believe that Vienna 

 is also preparing one, also descriptive. These jjamphlets 

 would enlighten those who wish to know something trust- 

 worthy on the nature of these curious bodies. 



THE IXTER-OCEANIC SHIP 

 RAILWAY. 



(Continued from p. 193.) 



THE pontoon, or floating-dock (see Figs. 2 to G), is of 

 the same general construction as those in use all over 

 the world, save in some impDrtant modifications rendered 

 necessary to fit it for its special work. For it is not 

 enough that the vessel should be docked and lifted out of 

 the water, but that it shall be caused to rest upon a cradle 

 in such a manner that its weight shall be equalised fore 

 and aft, and thus enable the carriage with its load to move 

 easily and safely. This is effected by means of a system 

 of hydraulic rams arranged along an intermediate deck 

 about six feet below the upper deck of the jiontoon (see 

 Fig. 3). The arrangement of the rams is in both lateral 

 and longitudinal lines, the former standing a little less than 

 seven feet apart, the one from the other. The area of the 

 combined rams in each lateral line is the same ; the area of 

 the one ram under the keel forward or aft is equal to the 

 area of the five or seven rams amidships. They may be 

 connected and made to work in unison, so that the same 

 pressure per square inch of surface of the rams will exist 

 throughout the whole system, or they may be disconnected 

 by valves, so that a greater pressure may be brought upon 

 the rams in a certain section or on a certain line. 



It is no part of the duty of these rams to lift the vessel. 

 They are designed only to resist its weight as it gradually 

 emerges from the basin. They get their power from a 



powerful hydraulic jnimp placed on a tower alli.ved to the 

 side of the pontoon, and rising and sinking with it, but 

 of such a height that, even when the pontoon rests upon 

 the biittoni of tho dock, it is nut entiri'ly submerged. The 

 pontoon itself is directed by powerful guides, which cause 

 it to descend and emerge from tho water always in the 

 same position. 



A ship Iniving entered the mouth of the Coalzacoalcoa 

 River, on the Atlantic side, and come up to the basin, tho 

 carriage with its cradle is run on to the floating dock ; then 

 water is let into tho compartments of the pontoon, and dock 

 and cradle gradually sink to tho bottom. Thi'ii tho ship is 

 brought in from tho exterior basin, and so adjusted as to 

 position that her keel will bo immediately over the con- 

 tinuous keel block of the cradle, and her centre of gravity 

 over the centre of the carriage. Tho water is then pumped 

 out of the submerged ]>ontoon in the manner employed in 

 floating-dock systems, and it rises gradually, bringing the 

 cradle up under the ship's hull (see Fig. 3). As soon as 

 the keel-block of the cradle is close to the .ship's keel, the 

 hydraulic pump is called into action, and pushes up the 

 pt-ndent rods and (losts of the supports gently against the 

 vessel, closely following the lines oi her hull and the run 

 of the bilge. The pressure upon the rams increases as the 

 vessel emerges from the water. 



In the case of a ship weighing 5,000 tons, each of the 

 fifty lines of rams would, of course, be called to sustain a 

 bui den of exactly 100 tons; tnd these lines bring placed 

 at equal dist^inces the one from the other, it will readily be 

 seen that each unit of the ship's weight is equally distri- 

 buted. The weight and displacement of the vessel is 

 learned from the pressure-gauge on the hydraulic pump. 



The vessel being clear of the water, hauH-wheels, or 

 arljustit'g-nuts that uiove in threads cut in the columns of 

 the supports, are run down to the bearings in the girder- 

 plates, whereupon the valve is opened and the rams with- 

 drawn, leaving the girders to support the weight of the 

 ship. Now each girder has the same number of wheels, 

 and, as described above, bears its just iiropo.'tion of weight 

 and no more ; hence each of the multitude of wheels tinder 

 the carriage is called upon to bear the i^ame weight. This 

 weight has been calculated to be only from eight to nine 

 tons, though the wheels will be tested to twenty. 



One of the many ingenious contrivanc s in the scheme 

 is the " hydraulic governor," so called, and by which the 

 unevenness of the plane of the jiOLitoon, when it comes to 

 the surface with its load, can be readily conected. This 

 apparatus is thus described : — " Two cylinders are attached 

 to each corner of the dock, one being upriuht and the 

 other inverted. Plungers attached to the pontoons move 

 in them. These two cylinders are connected by pipes, and 

 all spaces in the cylinders and pipes are filled solid with 

 water. As the pontoon rises, the water forced out of one 

 cylinder by the ascending plunger is forced into the in- 

 verted cylinder on the diagonal coiner where the plunger is 

 being withdrawn. Kow, if there is, say, 100 tons pre- 

 ponderance on one end of the pontoon, one half this weight, 

 or 50 tons jiressure, will be exerted by each plunger on 

 that end upon the water in its cylinder. This pressure is 

 instantaneously transniitttd through the pipes to the water 

 in the top of the upright cylinder in the opposite diagonal 

 corner, which acts with the same amount ot pressure as a 

 water-plunger upcn the metal plunger to hold it down ; 

 thus an equilibrium is maintained, and the pontoon com- 

 pelled to rise and fall perfectly level. It is possible, by aid 

 of a pressure gauge attached to the pipes, to ascertain the 

 exact amount of the excess of weight, so that, should this 

 gauge show too great a iirepondorance, the jiontoon must 

 be lowered, and the ship placed in a new position." 



