490 



NATURE 



[March 22, 1894 



termined by the intersection of the line joining the slit and the 

 grating, with a line drawn through the focus at a tangent to 

 the circle having its centre in the middle of the line joining the 

 grating with the focus. It is further suggested that the special 

 qualities of a Rowland grating which are due to its astigmatism 

 may be imparted to a "dioptric" spectroscope by giving a 

 slight convex spherical curvature to one of the prisms, so that 

 the instrument becomes slightly astigmatic. 



THE INSTITUTION OF NA VAL ARCHITECTS. 



LAST week the Institution of Naval Architects held their 

 annual spring meeting, under the chairmanship of Admiral 

 Sir John Dalrymple Hay, one of the Vice-Presidents of the 

 institution, the President, Lord Brassey, being absent abroad. 

 There was an unusually strong list of papers ; perhaps almost 

 too strong, for it was impossible to do justice to the sixteen con- 

 tributions, to say nothing of the formal proceedings and the 

 chairman's address, within the limited space of a ihree days 

 meeting. Some of the papers might have been referred back to 

 the authors with advantage, notably the two long contributions, 

 one on the detachable ram, and the other on the comparative 

 merits of the cylindrical and water-tube boilers. 



The following is a list of the papers on the agenda :-(i) 

 " The qualities and performances of recent first-class battle- 

 ships," by W. H. White, C.B., Assistant-Controller of the 

 Navy, and Director of Naval Construction ; (2) " The amplitude 

 of rolling on non-synchronous waves,'' by Emile Bertin, 

 Directeur de I'Ecole d'Application Maritime, Paris ; (3) "The 

 stresses on a ship due to rolling,'' by Prof. A. G. Greenhill, 

 Royal Artillery College, Woolwich; (4) "On Leclert's 

 theorem,"' by Prof. A. G. Greenhill ; (5) " Recent experi- 

 ments in armour," by Charles E. Ellis, Managing Director of 

 John Brown and Co., Limited, Sheffield; (6) "The detach- 

 able ram, or the submarine gun as .a substitute for the ram," by 

 Captain W. H. Jaques, late U.S. Navy ; (7) "Leaves from a 

 laboratory note-book : (a) some points affecting the combustion 

 of fuel in marine boilers : {b) the spontaneous heating of coal," 

 by Prof. 'V. B. Lewes, Royal Naval College, Greenwich ; (8) 

 " The circulation of water in Thornycroft water-tube boilers," 

 by J. I. Thornycroft; (9) "On water-tube boilers," by J. T. 

 Milton, Chief Engineer Surveyor Lloyd's Registry of Shipping ; 

 (10) " On the comparative merits of the cylindrical and water- 

 tube boilers for ocean steamships," by James Howden ; (li) 

 " Further investigations on the vibration of steamers," by Otto 

 Schlick ; (12) " On the relation between stress and strain in the 

 structure of vessels," by T. C. Read and G. Stanbury, assis- 

 tants to the Chief Surveyor Lloyd's Registry of Shipping ; (13) 

 " Steam pressure losses in marine engines," by C. E. Stromeyer, 

 Engineer Surveyor Lloyd's Registry of Shipping; (15) "Ex- 

 perience with triple expansion engines at reduced pressures," by 

 D. Croll ; (16) " Fluid prei>&ure reversing gear," by David Joy, 



M. Bertin's paper and Prof. Greenhill's second paper were 

 taken as read. 



Mr. White's contribution had been looked forward to with 

 some interest, as it was anticipated that a somewhat lively dis- 

 cussion would ensue between the constructors of the Admiralty 

 and naval officers on the question of the rolling of the 

 Resolution, a subject dealt with by the author. Although the 

 admirals mustered in some force, the discussion was of a very quiet 

 nature, and the general opinion was that the Resohtiiou and her 

 sister-ships are perfectly safe vessels, and quite as well designed 

 in regard to rolling capabilities as the tried battle-ships which 

 have preceded them. That this fact could be shown by scien- 

 tific reasoning was known beforehand to those acquainted with 

 the elements of design of ihe ships, and having sufficient technical 

 knowledge to draw conclusions from the premises. Never- 

 theless the doubts raised by the fact that the Resolution had put 

 back to port after encountering a heavy storm in the Bay of 

 Biscay, and the certainly extravagant newspaper reports of the 

 occurrence were an unpleasant feature, especially as they ap- 

 peared to be shared by a ceitain number o) naval officers. It is 

 well, therefore, that the discussion look place, and the matter 

 has been set at rest. Mr. White's was a very long contribution, 

 far too long for us to attempt even to abstract it here ; but it 

 was none too long for the patience of the meeting, as it was full 

 of suggestive matter from beginning to end. The author dealt 

 in a masterly way with the questions, in relation to battle-ships, 

 of draught and trim, stability, metacentric height, curves of 



NO. 1273, VOL. 49I 



statical stability, period of oscillation, bilge keels, behaviour at 

 sea, the behaviour of the Resolution in December 1893, per- 

 formances under steam, manoeuvring powers, relative size and 

 cost of Royal Soz'ereigjt class, and the Centu7-ion and Barjleur 

 class. Unfavourable comments have been made on the Royal 

 Sovereign class — the eight battle-ships of the Hamilton pro- 

 gramme, of which the Resolution is one — because they have 

 rolled heavily when small vessels have been comparatively 

 steady. This, of course, is a circumstance for which the 

 laws of nature are responsible rather than the designers of the 

 ship ; for however talented a naval architect may be, he cannot 

 destroy natural laws, but can only seek to work so that they may 

 be on his side, rather than fly in their face. To this end the 

 constructor attempts to dispose dimensions and weights so 

 that the natural period of oscillation of the ship may not syn- 

 chronise with the period of waves more commonly encountered. 

 A fair metacentric height is, of course, necessary in order that 

 the ship may have stability, but an unduly large metacentric 

 height tends to lessen the period of oscillation, and thus brings 

 the period of the ship more nearly into harmony with that of 

 waves ordinarily occurring. In fact, excessive stiffness produces 

 undue motion amongst waves, whilst a very steady comfort- 

 able vessel might be one in danger of turning over under very 

 small impulses. These facts are well known, of course, to those 

 accustomed to the design of vessels, but they apparently are not 

 fully grasped by many of those who go to sea in ships, to judge 

 by the correspondence called forth by the Resolution incident. 

 After the discussion that has been called forth by that incident, 

 and the instruction given in connection with it, a hope may be 

 expressed that "stability" and "steadiness" will not always 

 be taken to accompany each other. 1 he metacentric height of 

 the Royal Sovereign class of the barbette type is '^\ feet, and 

 past experience has shown that an excellent combination of 

 stifTness and steadiness has been obtained with metacentric 

 heights varying from 25 to 35 feet. It may be taken for granted 

 that it is desirable to give vessels a long period in order to gain 

 steadiness, and with these big vessels the metacentre could be 

 higher than in smaller craft, and, under extreme conditions of 

 lading, the Royal Sovereign class could have as great a height 

 as 4 feet wiihout unduly impairing their prospect of steadi- 

 ness, whilst of course the stiffness would be great. It is worthy 

 of note that the inclining experiments made with the Royal 

 Sovereign showed the calculated centre of gravity to be but 

 if inches above the actual position ; a result which speaks well 

 for the care with which designs are got out at Whitehall. The 

 period of oscillation of the Royal Sovereign with normal weights 

 and 2)2 '^^t metacentric height, is about eight seconds. This 

 accords with the period- of battleships which have acquired good 

 reputations for steadiness in times past. Most of the latter ships, 

 Mr. White tells us, have smaller metacentric heights, but they 

 are also inferior in weight and moment of inertia ; the latter, 

 it must be remembered, having an important influence on the 

 period of Oscillation. Mr. White did not think it necessary to 

 explain to a professional audience the manner in which rolling 

 depends on the agreement between the period of the ship and 

 the period of the wave, a fact that must be apparent to anyone 

 who considers how a child's swing may be caused to oscillate 

 through a wide range by small impulses applied at the right 

 moment. Apparently the Resolution fell in with a sea, on the 

 memorable occasion in the Bay of Biscay, which tilted her from 

 side to side just as she herself was inclined to roll, whilst the 

 little torpedo gun-boat Gleaner, which accompanied her, and 

 made so much better weather of it, was not "fitted " by the big 

 sea. In more moderate and more ordinary weather the relative 

 conditions might have been reversed. In any case, it is as well to 

 repeat, the Resolution at her greatest angle of roll had an ample 

 margin of stability, and there was no reason to fear for the ship, 

 although it was doubtless remarkably uncomfortable on board, 

 and the captain exercised a wise discretion in coming back, 

 having, as he did, an entirely untrained crew under him. 



The paper by M. Emile Bertin treats with the subject of 

 rolling of ships from a mathematical stand-point, carrying on the 

 investigation of the question from a point where it was left by 

 the late Prof. Jenkins, in a paper wherein he investigated the 

 maximum effect which takes place at the extreme angle of roll. 

 The author extends the theory to the effect at any intermediate 

 part of the oscillation, and to the case in which the angle of 

 maximum-righting moment may be less than a right angle. •• 

 The diff.culty of exact measurement of rolling is shown by the 

 paper ; a fact also well illustrated by Mr. White in the previors 



