540 



NA TURE 



[April-], 1887 



result was that the total weight of each ship was increased 

 by 415 tons. Moreo\er, the present Board of Admiralty 

 have decided that uar-ships are in future to coal up to 

 their full stowage capacity ; that is to say, in the case 

 of the Impc'rieuse and Warspik 500 tons more fuel are to 

 be carried than the designer allowed for. As a natural 

 consequence, the addition of 915 tons to the total 

 weight of each vessel has immersed these ships so deeply 

 that the height of the armoured belt above water has 

 been reduced from 3 feet 3 inches to a little under i foot, 

 and there are not wanting those who declare that this 

 circumstance greatly injures, if it does not totally destroy 

 their fighting efficacy. Sir Nathaniel Barnaby very suc- 

 cessfully proved that the responsibility for the additions 

 to the weights of the hull and machinery belon.'s to the 

 then Board of Admiralty, and not to himself. He also 

 demonstrated that the addition of the extra 500 tons of 

 coal was a case of deliberate reversal of the policy of one 

 board by its successor, but, judging from the tone of the 

 discussion, he failed to convince his audience that the 

 original policy of calculating the immersion of the belt on 

 a fuel-supply of 400 tons was a wise one. 



Mr. Biles's paper, above referred to, on the armour 

 question, was an interesting and useful attempt to solve a 

 difficult problem. He commenced by taking, as the basis 

 of a defitiite comparison, the latest type of British belted 

 cruiser, viz. the Aurora, of 5000 tons displacement This 

 vessel has a belt 5 feet 6 inches wide, of which i foot 

 6 inches is above the load-line ; the thickness of the belt 

 IS 10 inches, and its top edges are united bv an armoured 

 deck 2 inches thick, under which are placed all the vitals 

 of the vessel. With this he compares a type of cruiser 

 without any side armour, but protected b'v means of a 

 u u ^'^'^' ^'^^ ^"'^^ °^ vi\-\\c\i curve down so as to join 

 the bottom some feet below the water-line, the curved or 

 sloping portions of the deck being covered with armour 

 of the same horizontal thickness as the Aurora's belt. In 

 making the comparison he assumes — 



(i) That the length and draft of the proposed vessel are 

 to be the same as in the case of the Aurora. 



(2) That the displacements are to be the san.e in each 

 case. 



(3) That the costs are to be the same. 



Mr. Biles claims that in design No. I the internally 

 protected vessel would weigh less than the belted cruiser 

 by about 210 tons ; that it would cost nearly 40,000/. less ; 

 and that the designer would have the option, on the 

 smaller displacement, of either increasing the thickness 

 of the flat portion of the armoured deck by 40 per 

 cent, amidships, or of adding about six-tenths of a knot 

 to the speed, or finally of adding one 9-2-inch gun and 

 two 6-inch guns to the armament. 



In the case of design No. 2, where the displacements of 

 the two types are equal, it is estimated that either a knot 

 and a half might be added to the speed, or else that the 

 thickness of the whole of the deck-plating might be in- 

 creased by 44 per cent. 



Lastly, on the assumption that the cost of the vessels is 

 the same, Mr. Biles claims for the internally protected 

 vessel the following important advantages ; viz. 20 per cent, 

 greater thickness of protection on the slope of the deck' 

 50 per cent, more on the flat, two more guns of the heaviest 

 calibre, 20 per cent, more coal, and one knot additional 

 speed. Mr. Biles very pertinently asks the question. Is 

 the adoption of the belt worth the extra money paid for it 

 with Its accompanying sacrifices ? or. If the money is to 

 be spent, is the belt worth the sacrifice of speed, protec- 

 tion, and armament, which is entailed in its adoption ? 



The papers on marine engineering were not quite so 

 interesting as some which have been read at recent meet- 

 ings of the Institution. There were three on the subject 

 of screw propellers, by Prof. Cotterill, F.R.S., Mr. Cal- 

 vert, and Mr. Linnington of the Admiralty, and one on 

 the machinery of small boats, by Mr. Spyer, also of the 



Admiralty. In addition to the foregoing there were two 

 papers on stability, a subject which has been perhaps 

 lately somewhat overdone ; and an important contribution 

 by Mr. Archibald Denny on the practical application of 

 stability calculations in relation to the stowage of steam- 

 ships. Mr. Jenkins, the newly-appointed Professor of 

 Naval Architecture at Glasgow University, prepared a 

 paper on the subject of the shifting of cargoes. 



yi 



5 TROME YER'S S TRAIN-INDICA TOR 

 HIS is a very useful and ingenious apparatus for 

 measuring the extension or compression produced 

 on any rnaterial by tensile or compressive forces. Such 

 deformations having been observed, the corresponding 

 variation in the stresses to which the material has been 

 subjected may at once be inferred by the ordinary law of 

 elasticity connecting strains and stresses in solid bodies. 

 The instrument affords one of the many examples of the 

 valuable results obtainable bv the simplest possible 

 mechanical means— results which before the construc- 

 tion of the strain-indicator were considered altogether 

 unattainable. 



The instrument is shown in the woodcut, and consists 

 of two flat plates, T, b, about ij inch wide and of any 

 convenient length, pressed together by means of two 

 springs, s, s, in such a manner that one plate projects at 

 one end and the other at the other end. The plates are 



free to slide over each other at their ends opposite h. 

 Fixed centre-points, c, C, are screwed one into each end 

 of each plate, and a graduated dial, D, is attached to the 

 upper one of the two plates T. Two of these instruments 

 are held together by a pair of clamps, K, K, fixed ju- 1 over 

 the centre-points, which, when screwed tight, press the 

 centres against both sides of the test-pieces ; for safety 

 against slipping, a few taps of a hammer embed them 

 more firmly. The figure shows a round bolt about to be 

 operated upon by tensile force, the screwed ends forming 

 attachments to the grips of the testing-machine. Then, 

 when everything is ready, a pair of very fine hardened 

 steel wire rolling pins, P, p, to which light pointers have 

 been attached, are inserted between the plates. These 

 rolling pins, when in position, should be in the centres of 

 the dials. On applying the load to the test-piece, elonga- 

 tion takes place ; the centre-points move slightly away 

 from each other, carrying the plates with them, which, as 

 they move in opposite directions, and as they are held 



