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NATURE 



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speed, in the vessels so tried. Previous to that time it 

 had been generally considered that it was sufficiently 

 accurate for ordinary purposes to ascertain the power 

 necessary to drive a ship at one or two different speeds 

 only, and to assume that the resistance at other speeds 

 would vary as the square of the speed. The errors often 

 involved by this assumption were known to be consider- 

 able ; but the practice was not improved upon until the 

 introduction of Mr. Froude's curves of resistance for 

 models, and Mr. Denny's corresponding curves for actual 

 ships. 



In 1873, Mr. Denny entered into correspondence with 

 Mr. Froude, and communicated to him from that time 

 forward the results of his experiments upon the speed of 

 ships. Those results, when compared with what were 

 given by model experiments, were of great assistance 

 to Mr. Froude in his investigations. Mr. Froude said, 

 at the Institution of Naval Architects, in 1876 : "Mr. 

 Denny's horse-power results, when closely scrutinized, 

 were found at once to supply most important information 

 on the subject of engine friction ; and they have helped 

 to corroborate and further elucidate certain general con- 

 clusions on the subject of the expenditure of power in 

 propulsion, which other less crucial tests had enabled me 

 to arrive at approximately." Mr. Froude read a paper, 

 from which the foregoing is a quotation, in which he used 

 the data referred to for determining the ratio of indi- 

 cated to effective horse-power in ships. He also read a 

 second paper, at the same meeting, in which he said 

 that " the trial of Mr. Denny's ship Merkara, referred to 

 in the paper I have already read, furnished materials for 

 extending and giving practical completeness to a com- 

 parison [of the resistances of long ships of several types] 

 which our series of experiments had already led us to 

 institute between several types of form." This furnishes 

 an excellent illustration of how progress may be facili- 

 tated by the close co-operation of the scientific investi- 

 gator and experimentalist with the practical worker who 

 requires to understand and apply the teachings of science ; 

 and it is one proof out of many of the scientific value of 

 Mr. Denny's early speed trials, and of his readiness 

 to communicate freely the results to others interested 

 in the subject. Mr. Denny laboured with great enthu- 

 siasm to perfect the data obtained on measured mile trials 

 of ships, and to collect and record it systematically ; and 

 he was always ready to place such information at the 

 disposal of other workers in the same field. 



Mr. Denny read a paper, in 1875, before the Institution 

 of Engineers and Shipbuilders of Scotland, on " The 

 Difficulties of Speed Calculations," in which he strongly 

 insisted upon th6 uselessness of the ordinary speed for- 

 mulas, and urged the desirability of having all steamers, 

 if possible, tried progressively. He gave conclusive force 

 to his arguments by exhibiting curves of power and 

 speed for several ships, which showed large departures 

 ,of the curves given by the standard formulas from the 

 curves which had been deduced from actual trials of 

 the ships. He iiever afterwards ceased to call attention 

 to the great advantage of the improved system of speed 

 trials ; and he soon had the satisfaction of seeing it brought 

 into general use. Mr. Froude said, in 1876, in one of the 

 papers above referred to : "It is to Mr. Denny's honour 

 that, finding the so-called constants [in the speed formulas 



then in use] were invariably variable and inconstant, he 

 determined of himself to strike out a new line, and find 

 out by trial what is fact, instead of contenting himself with 

 assuming what ought to be the relation between indicated 

 horse-power and speed." 



In 1881, Mr. Denny, with the consent of his partners, 

 took the important step of erecting an experimental tank 

 in the shipyard at Dumbarton for the purpose of carrying 

 out independent trials of the resistance of models such as 

 Mr. Froude had long been doing at Torquay. So long 

 before as 1877 he said at a meeting of the Institution 

 of Naval Architects : " The attention of all mercantile 

 naval architects should be called to the fact that all ] 

 Mr. Froude's experiments bear strongly and directly ' 

 on our work ; and unless we follow them thoroughly and 

 follow them accurately, and with an anxious spirit, we 

 shall not succeed as we ought in taking the lead of those 

 countries interested in shipbuilding." His biographer 

 says that in 1 881, when a large extension of the Dumbarton 

 shipyard was commenced, "the erection of an experi- 

 mental tank became a subject of serious consideration 

 with Mr. William Denny. He had become convinced 

 that the expenditure involved in the construction and 

 maintenance of such a tank would ba justified by its 

 utility. The result was that the present Dumbarton 

 tank, the only one either in existence or in contemplation 

 under private control, was devised, constructed, and 

 equipped." The magnitude and difficulty of the work 

 will be understood when it is remembered that the water- 

 space contained in the so-called tank is 300 feet long and 

 22 feet broad, and the depth of water 9 feet ; that the 

 models experimented upon are fashioned out of solid 

 paraffin by mechanism originally devised by Mr. Froude 

 for the purpose ; and that the models are towed from 

 end to end of the tank by means of an overhead 

 carriage fitted with delicate apparatus for accurately mea- 

 suring the speed of the model and the force applied 

 to maintain it at that speed, and for automatically pro- 

 ducing a graphic record, in a form suitable for subse- 

 quent measurement and calculation, of the results 01 

 each experiment. The outlay and thought demanded 

 by such an extensive, complicated, and novel under- 

 taking was very great ; but the greatest difficulty of all 

 would be the formation of a staff competent to make it 

 fruitful and successful in results. Mr. Froude was a man 

 of genius, and everyone could not work with his tools. 

 However, Mr. Denny soon organized a staff of skilled 

 assistants who have proved their fitness for the task to 

 which they were put. Prof. Bruce says that " since the 

 tank was opened some twenty thousand experiments 

 have been made on models of ships previously built and 

 tried on the measured mile, or of ships in process of 

 design, or of ideal ships conceived for the purposes of 

 experiment." 



Mr. Denny did much to simplify and improve the 

 methods of calculation for determining a ship's stability, 

 and to apply the known science of the subject to the 

 practical work of the designing office. In 1880 he com- 

 menced the practice of ascertaining by experiment the 

 position of the centre of gravity of every ship built by 

 his firm ; and the data thus obtained for numerous ships 

 were perfected and carefully systematized for guidance 

 in the preparation of new designs. Amsler's mechanical 



