March 22, 1894-] 



NA TURE 



491 



contribution. The ordinary pendulum instrument has been 

 'known to give indications 50 per cent, from truth, and it is 

 evident that all statements as to the rolling of ships at sea- 

 other than those obtained by a trained staff of observers with 

 approved appliances — must be taken with a very large grain of 

 salt. 



On the second day of the meeting, Thursday, March 15, the 

 ■proceedings opened with Mr. Ellis's very interesting paper on 

 armour. This was another long contribution, with an appendix 

 which gave results of all firing experiments on nickel steel and 

 Harveyised armour that have taken place, excepting two, and 

 one of these is to be included later. The other was made with 

 a Harveyised steel plate so manifestly inferior as not to be con- 

 sidered fairly within the category. There was not much dis- 

 cussion of results or expression of opinion in the paper, and it 

 would be useless to attempt to abstract the details of the trials. 

 The memoir will remain a standard record of what has been 

 done in this field up to the present time, and as such we must 

 be content to leave it. The discussion which followed was much 

 of the same nature as the paper; but the gratifying fact seemed 

 apparent that at present English makers of armour-plates ai-e 

 somewhat ahead of their foreign competitors. How long it will 

 be before the see-saw of inventive progress will again put another 

 country in the front, remains to be seen, and doubtless depends 

 chiefly to what extent monopoly is allowed to rule. 



The leaves from Prof. Lewes's laboratory note-book did not 

 form quite so valuable a paper as we are accustomed to get from 

 him. A good deal that was said about combustion was certainly 

 •not new, even to the common engineer who has not made a 

 ■special study of chemistry, and the many practical points missed 

 seriously detracted from the value of the matter set forth. Thurs- 

 day evening's sitting was the big one of the meeting, indeed we 

 have seldom seen the theatre so overcrowded as it was when Sir 

 Nathaniel Barnaby took the chair at seven o'clock. The water- 

 tube boiler is the great marine engineering question of the day, 

 and there was a prospect of it being fully discussed after the 

 reading of the three papers that were on the list. The boiler has 

 never received the attention it deserves at the hands of engineers, 

 the steam-engine apparently affording a much more interesting 

 field of research. The neglect has carried with it its own 

 punishment, for the boiler has always been the most fruitful 

 source of trouble to the marine engineer. To such an extent 

 ■has this been the case of late that engineers have perforce had to 

 turn their attention to the less interesting branch of machinery 

 design. The advent of the three-stage compound engine, and 

 the consequent demand for higher pressures, has emphasised the 

 need for a new departure, although the introduction of the 

 corrugated flue and the application of steel to boiler con- 

 struction has delayed the crisis somewhat. These advantages 

 have, however, been fully worked up, yet still there is 

 a demand for further advance, and a large number of 

 prominent marine engineers appear to think that the 

 water-tube boiler, or pipe boiler — in which the water is inside 

 the tubes, and the fire outside — is the proper solution of the 

 problem. Mr. Thornycroft — the well-known torpedo boat 

 builder, who took the leading part in introducing the locomotive 

 type of boiler afloat — was perhaps the earliest of the present- 

 day advocates of the water-tube boiler in this country to experi 

 ment and invent. The result of his labours is that he has 

 produced a water-tube boiler at once safe, quick steaming, light, 

 economical, and durable. The chief point which has led to the 

 attainment of these desirable qualities is that he has been 

 able to combine automatic and sufficient water circulation with 

 small water spaces. His boiler consists of three horizontal 

 cylinders which are placed so that in cross section of the boiler 

 they are at the three angles of an imaginary triangle. The top 

 cylinder at the apex is connected to the two cylinders at the base 

 by two series of curved pipes which form the heating surface of 

 the boiler. The grate is under the base of the triangle, and the 

 whole is enclosed in a smoke-jacket or casing, the chimney 

 naturally being at the top. The products of combustion pass 

 among the tubes, and thence up the chimney. Outside the casing 

 the top cylinder is connected to the two bottom cylinders by a 

 couple of large pipes. The top cylinder may be from a foot to 

 three feet in diameter, according to the size of the boiler ; the 

 bottom cylinders are considerably smaller, and the pipes form- 

 ing the heating surface will be about one inch in diameter. The 

 circulation of water, the chief feature which has led to the suc- 

 cess of this steam generator, is obtained in this way ; — When 

 the one-inch pipes become heated, the water in them is 



NO, 1273, VOL. 49] 



turned partly into steam, and thus the mass becomes of less 

 specific gravity than the column of solid water in the down- 

 comer pipes outside the casing which connect the extreme end 

 of the top cylinder to the extreme ends of the bottom cylinders. 

 An ascending current of steam and water is thus set up in the 

 tubes, whilst there must necessarily be a descending current in 

 the down-comer pipes to compensate. In this way the water 

 is always travelling round in a continuous stream, up the hot 

 steam generating pipes, and down the colder down-comer pipes 

 outside. Mr. Thornycroft has made some very pretty e<peri- 

 ments with one of his boilers, which welately had an opportunity 

 of seeing at his works at Chiswick. He fitted a glass end — 

 made of a number of sheets of plate-glass stuck together by a 

 transparent cement — to the top horizontal cylinder, so that the 

 circulation could be seen and measured. For the latter purpose 

 a notched weir was put in the end of the cylinder, and the flow 

 over it gauged according to the usual formula. The ends of the 

 steam generating tubes could be seen spurting out water inter- 

 mittently, and the circulation of water is so thorough that it was 

 found by the weir measurements that the circulation of water 

 was 105 times as rapid as the evaporation ; that is to say, 

 for each pound of steam generated 105 lbs. of water passed 

 round the system, or, in other words, an equivalent of every 

 pound of water passed 105 times round the cycle before being 

 evaporated. It will be evident that with a volume of water 

 sweeping with a rapidity such as this through the generating 

 tubes, the surface would not be likely to be overheated, what- 

 ever the rate of combustion might be, and however fierce the fire. 

 The problem of "drowned tubes ' v. "above-surface tubes," 

 which appears to be likely to be the burning question of the 

 hour in water-tube boiler circles, is one into which we cannot 

 enter here. Mr. Thornycroft is the leader of the "above- 

 surface " school, whilst his great rival of the lower reaches, Mr. 

 Yarrow, heads the "drowned tube" believers. Undoubtedly 

 the Thornycroftians have more rapid circulation on their side ; 

 the question arises whether the Yarrovians have circulation 

 enough. 



Mr. Milton's paper consisted of a description of various types 

 of water-tube boiler at present before the engineering world. 

 It contains a large number of illustrations, and forms a valuable 

 addition to his paper on the same subject read at the last summer 

 meeting of the Institution held in Cardiff. Of Mr. Howden's 

 paper it is not necessary to speak. 



Friday's proceed inj^s opened with a most interesting paper 

 by Mr. Otto Schlick, whose investigations into the question of 

 vibration of steam vessels will become classic. Tnis further 

 contribution carries the problem a step further, or, perhaps it 

 should be said, enables the engineer to draw his conclusions 

 with greater clearness. By means of a model designed to repre- 

 sent the hull of a steam vessel, the author showed the effect of 

 placing various engines in different parts of the vessel. There 

 were engines of many types — single, double, triple, and quad- 

 ruple cranks. Pistons were weighted to represent difference in 

 sequence of cylinders, and cranks were arranged at various 

 angles. The model engines were shifted from part to part of the 

 plank which represented the hull of the vessel. This plank, 

 suspended from a frame by helical springs, naturally had a period 

 of vibration of its own, which period was of the first order, i.e. 

 with two nodal points ; and as lbs engines were placed upon the 

 nodes orelse in other positions, thevibration was intensified or not 

 when the revolutions of the engines reached that critical number, 

 when synchronism was obtained between revolutions and the 

 period of vibration of the plank or hull, according to the now well- 

 known rule. We cannot pretend to give all the varying changes 

 that were rung by Herr Schlick upon his model. Sometimes 

 the changing of the high pressure for the low-pressure piston 

 would start most violent oscillations, or vice versa, whilst the 

 shifting of the engines to an equivalent of a few feet in an 

 actual ship would have a really wonderful effect. For the details 

 of these experiments we must refer our readers to the original 

 paper, wherein both naval architects, engineers, physicists, and 

 mathematicians may find matter of much interest. 



Messrs. Read and Stanbury's paper is one of that admirable 

 series on the subject of stress and strain in vessels upon which 

 the first-named author especially has devoted so much time and 

 thought. The present is a paper of almost purely pro- 

 fessional interest, and is one with which it would be impos- 

 sible to deal in brief. Mr. Taylor's paper was not read, Mr. 

 Froude, in the absence of the author, giving an abstract. The 

 problem of calculating thej pressure and_ velocity of water at 



