June 27, 1895] 



NATURE 



207 



light produced. So much is that to be anticipated, that I pre- 

 dicted in 1888 that when we got any indications of stars the 

 spectra of which showed that they were really sparse swarms, 

 such as that depicted on the diagram, at the maximum of their 

 luminosity we should get V>right lines, and in all probability 

 bright lines of hydrogen, visible in their spectra. It so hap- 

 pened that shortly after this prediction was made — and when a 

 man of science predicts he does it chiefly not for the sake of 

 influencing others, but to point out where the path of truth 

 really lies — I, in common with many other students in this 

 country, received from Prof Pickering a photograph of the s])ec- 

 trum of that most wonderful of all variable stars, commonly called 

 Mira, or the marvellous star (Fig. 33). We knew before we re- 

 ceived the photograph what its spectrum would in all probability 

 be, but the interesting point was to see whether or not there were 

 any bright lines in it. Vou see there is an obvious bright line at 

 that |rart of the spectnmi which represents the wave-length of 

 one of the hydrogen lines ; there is another where the wave- 

 length of another hydrogen line is represented, and there is 

 another very obvious bright line in another part of the spectrum. 

 So that this photograph entirely justifies the prediction that had 

 been made with regard to this class of stars. .\nd so well is 

 that now recognised that, quite independent of the meteoritic 

 hypothesis, one of the most characteristic features of this class 

 of stars is acknowledged to be the appearance at the top of the 

 light curve — at the moment of the greatest giving out of light — the 

 bright lines of hydrogen and possibly of other substances in the 

 spectrum. Forty old variables of this class show bright lines, 

 and twenty new variables have been detected by the appearance 

 of bright lines, i.e. bright lines being seen in them sugge.sted 

 that they were variable, and a further inquiry into the old records 

 showcfl that undoubtedly their light had varied, 



J. Norman Lockyer. 

 (To be continued.) 



THE INSTITUTION OF NA VAL 

 ARCHITECTS. 

 "T^ME summer meeting of the Institution of Naval Architects 

 has been held this year in Paris, and has proved one of the 

 most successful gatherings of the kind it has ever been our good 

 fortune to attend. It had become known amongst members for 

 .some time past that a very strong Reception Committee had 

 been formed, consisting of many French gentlemen, eminent 

 both in the scientific and naval world. A large part of the week 

 devoted to the meeting was given up to purely pleasure excur- 

 sions and entertainments. Of these it is not within our province 

 to speak, but it would be ungracious on the part of any English 

 journal, dealing with the meeting in any way, not to say a word 

 in recognition of the generous hospitality so lavishly displayed 

 by all those connected with the organisation of the programme 

 in France. 



There were three sittings for the reading and discussion of 

 papers; Lord Brassey, the President of the In.stitution, taking 

 the chair on each occasion. Members assembled for the first 

 time in the new amphitheatre of the .Sorbonne, which had been 

 kindly placed al the disposal of the Fxecutive by the Keclor of 

 the University of Paris, M. Octave Oreard. Vice-Admirsl 

 Charles Duperre, President of the Reception Committee, 

 welcomed the members, and Lord Brassey responded in a brief 

 address. 



The following is a list of the papers set down for reading and 

 discussion on the programme. 



" The Amplitude of Rolling on a Non -Synchronous Wave," 

 by tmile Bertin, Direcleur des Constructions Navales, and 

 Directeur de I'ficole d'.\pplication Maritime. 



" On W^jod and Copper Sheathing for Steel .Ships," by Sir 

 William White, Director of Naval Construction, and Assistant 

 Controller of the Na\-j'. 



"The.M.t;. Metre," by Archibald Denny. 



" On the utility of making the calculation of the total external 

 volume of ships, and of drawing out the complete scale of 

 solidity, from the triple point of view of tonnage laws, stability 

 and load-line," by \'. Daymard, Engineer in Chief of the 

 Compagnie (lenerale Transatlantique. 



"On Light Scantling Steamers," by B. Martell, Chief 

 -Surveyor Lloyd's Registry of Shipping. 



"On Coupling Boilers of Different Systems," by Pierre 

 Sigaudy, Engineer in Chief of the Forges et Chantiers de la 

 Medilerranee. 



NO. 1339, VOL. 52] 



" On the Cost of Warships," by Francis Elgar. 



" On some necessary conditions for resisting intense firing in 

 water tube boilers," by Augustin Normand. 



" On the Xiclausse Boiler," by .Mark Robinson. 



M. Bertin's paper, which was the first to be read, treated a 

 highly technical subject from a strictly mathematical point of 

 view. The author pointed out that perfect synchronism between 

 the period of rolling and of the wave is practically a purely 

 theoretical case. He referred to the latest calculations made 

 which bear upon a large number of particular cases, and also to 

 the principle of the graphic method, which has been previously 

 de.scribed, and which is a simple extension of the method 

 employed to determine the amplitude of rolling on a synchronous 

 swell. The subject is one of extreme interest, but we fear we 

 nmst refer those of our readers who are not acquainted with it to 

 the published paper in the volume of the " Transactions " of the 

 Institution. It would be impossible to give an abstract of M. 

 Bertin's mathematics, or, indeed, to make the matter clear with- 

 out the diagrams which accompanied the paper. One result, 

 however, which may be quoted, is that M. Bertin confirms the 

 facts brought out by Sir William White as to the great increase 

 of efficiency of bilge-keels in large as compared with small ships. 

 This, as our readers are aware, came somewhat as a surprise to 

 those engaged in these matters. M. Bertin states : " We find, 

 therefore, in bilge-keels a more powerful method of checking 

 hea\y rolling than has been foreseen. In a different condition 

 of things, free liquid provides a more rapid means of extinguish- 

 ing small rolls than could have been foreseen from any calcula- 

 tions founded on the known properties of liquids." M. Bertin 

 states that the question upon which he treats is one that cannot 

 be solved by calculation ; accurate observations made at sea are 

 the necessary complement of all the theoretical researches and 

 experimental study made in port. 



Sir William White opened the discussion on this paper. It will 

 be remembered that at the spring meeting of the Institution 

 the Director of Naval Construction was unable to be present, 

 owing to a verj' severe illness. In spite of this, a paper which 

 he had written on the subject now under consideration was read 

 in his absence. His reappearance at the meetings was the 

 occasion of a very general outburst of enthusiasm on the part 

 of the members present, for no one is more popular, and indeed 

 few have done more for the Institution, than Sir W^illiam White. 

 Sir William pointed out that for mathematical purposes it was 

 necessary to make assumptions which could be corrected by and 

 applied to practical work. He paid a handsome compliment to 

 the author by coupling his name with that of the late Mr. 

 Froude. 



The next paper read was Sir William WTiite's own contribu- 

 tion on sheathed ships. This, as the author pointed out, was a 

 direct contrast to the paper last read, being of a simply practical 

 nature. As is well known, the purpose for which steel vessels 

 of war are sheathed with wood, is in order that they may be 

 coppered, and their bottoms may thus be preserved from fouling. 

 It is needless to say that the wooden planking is applied as a 

 means of preventing [galvanic action between the ct.jpoer and 

 steel. In order to effect this, it is necessary that the planking 

 should be w-ater-tight, for sea water, in contact both with the 

 copper and the steel skin, would set up galvanic action. It may 

 be stated, however, in pa.ssing, that if the sea water is not in 

 circulation, the galvanic action will not be intense or continuous, 

 which is a fact that might be anticipated. In order to make the 

 planking water-tight, it was originally thought neces.sary that a 

 double skin should be used, and very elal«>ratc precautions were 

 taken in regard to fastenings. Sir William While, then Mr. 

 White, came to the conclusion that the double planking was un- 

 necessary, and that with proper care a single skin could be made 

 to answer the |)urpose required. In this he was opposed by a 

 large number of eminent authorities, but having the courage of 

 his convictions, he introduced the new system into Her Majesty's 

 Navy. The result has justified his anticipations, for after 

 several years' experience, the hulls of ships thus sheathed have 

 not been found to suft'er. 



.Mr. Archibald Denny's paper described a small instrument he 

 has invented by which the metacentric height of a vessel can be 

 ascertained. It is intended for the use of captains of ships, so 

 that they may ascertain the stability of their vessels under 

 various conditions of lo.ad and trim. "The instrument is&implya 

 spirit-level pivoted at one end and adjusted al the other, by 

 means of a micrometer screw. This combined with a dia- 

 gram gives the value M.G. The method of using the instru- 



