104 REPORT — 1842. 



riods of the stroke. This velocity is dependent in engines working expan- 

 sively upon the particular law, according to which the pressure of the steam 

 varies as its volume expands ; any such law being assumed, the velocity may 

 be expressed by a mathematical formula in terms of that law and of other 

 given elements of the question. The determination of it by experiment thus 

 supplies a means (and apparently the best) of verifying the different formulas 

 which have been proposed to represent the true law of the expansion of steam. 



M. Morin has himself kindly undertaken to superintend the construction of 

 one of his instruments for the use of the Committee. It is in the hands of M. 

 Breguet, and they hope to receive it early in November. 



Nothing has hitherto approached to the admirable accuracy of the admea- 

 surements stated to have been given by this instrument. It discriminates be- 

 tween spaces described in successive intervals of time, whose duration does 

 not exceed the 10,000th part of a second, and measures them. 



Report of a Committee on the Form of Ships. By John Scott 

 Russell, 31. A. 



It contained upwards of 20,000 observations, the result of careful experi- 

 ments on the resistance to models of ships of more than a hundred different 

 forms and sizes, and extending from small models of 30 inches long, to ves- 

 sels of 25 feet, 60 feet, and 200 feet long, and above 1000 tons burden. 

 These experiments were under the general superintendence of a Committee 

 of the Association, consisting originally of Sir John Robison, Mr. Scott 

 Russell, and Mr. Smith. Unfortunately, the ill-health of Mr. Smith's family 

 had altogether deprived the Committee of his advice and assistance, but the 

 observations were personally conducted by Mr. Scott Russell, who had to 

 acknowledge the pleasure he had derived from conferring with his friend 

 Sir John Robison, with whom he had frequent occasion to consult during 

 the progress of the observations. The smaller experiments had been made in 

 a reservoir in the ground attached to his (Mr. Russell's) residence, and the 

 larger ones in the open sea. It was probable that these results, maturely di- 

 gested, and illustrated by accurate drafts of the forms of the ships subjected 

 to experiment, would be published in such completeness as might be practi- 

 cally serviceable to the naval constructor and mercantile ship-builder ; and 

 he would therefore confine the present Report to a general account of the 

 objects contemplated in the experiments, and the method by which these 

 designs had been carried out. Several series of experiments have already 

 been made, both by scientific bodies and by public-spirited men, for the ad- 

 vancement of naval architecture. These had cost large sums of money, and 

 consumed much valuable time and talent. To most of them it had been ob- 

 jected — unhappily not without reason — first, that they had not been con- 

 ducted with an adequate knowledge of the Avants of the constructor ; se- 

 condly, that the forms of bodies submitted to experiment were by no means 

 such as are used by the ship-builder ; thirdly, that the scale on which these 

 bodies were constructed was too small to claim for the results, as applied on a 

 large scale, any considerable degree of confidence ; fourthly, that it had not 

 been established by what law the results of experiments on one scale of mag- 

 nitude are to be transferred to a different scale, either greater or less ; and, 

 fifthly, that the apparatus formerly used was liable to errors which it was 

 difficult to eliminate from the results. To obviate such objections was one 

 great object in these experiments. Mr. Russell had contrived a new appa- 

 ratus, which was so simple and convenient, that a uniform propelling force 



