STABILITY, PROPULSION, AND SEA-GOING QUALITIES OF SHIPS. 23 



Former Experiments on Resistance. 



The first important experiments were those made by Bossut, Condorcet, 

 and D'Alembert, by direction of Turgot. The results were published as a 

 separate work in 1777, and a very full abstract of them is given by Bossut 

 in his ' Hydrodynamique.' The chief results are summarized by Bossut as 

 follows : — - 



That the resistance of the same body at different speeds, whatever be 

 its shape, varies very nearly as the square of the speed. 



That the direct head-resistance of a plane surface is sensibly propor- 

 tional, at the same speed, to the area of the surface. 



That the measure of the direct resistance of a plane surface is the 

 weight of a fluid column which has that surface for its base, and whose 

 height is that due to the velocity. 



That the resistance to oblique motion, other things being alike, does 

 not diminish by a law at all approaching that of the squares of the sines 

 of angles of incidence ; so that for sharp entrances, at least, the former 

 theory must be completely abandoned. 

 Mr. Scott Russell has remarked that between certain limits the observed 

 resistances of wedge-bows could be represented with a close degree of ap- 

 proximation by a formula of the form 



^-^G-^^y 



where K is a constant, tt stands for 180°, and e is the angle of the wedge, 

 which is supposed to be of not less than 12°, and not more than 144°. See 

 his ' Naval Architecture,' p. 168, and ' Transactions of Civil Engineers,' vol. 

 xxiii. p. 346. 



The next experiments of importance are those of De Chapman, published 

 in his ' Architectura Navalis Mercatoria.' The result of these has already 

 been mentioned. He performed some fresh experiments at Carlscrona, in 

 1795, wliich seemed to lead to somewhat different conclusions. See Inman's 

 translation of De Chapman, pp. 41 and 257. 



We then come to Beaufoy's experiments in the Greenland Dock from 

 1794-98. This enormous series of experiments can only be regarded as 

 establishing very few facts, among which we may mention : — 



That the resistance to oblique surfaces does not vary as the sine 

 squared of the angle of incidence. 



That for unfair bodies, such as he experimented upon, the resistance 

 increases faster than the square of the velocity. 



That increase of length, within certain limits, has a tendency to de- 

 crease resistance. 



That friction of the wetted surface enters largely into the resistance. 



That friction of the wetted surface appeared to increase in a ratio 



somewhat less than that of the velocity squared, — between v^'' and v^'^. 



He also arrives at the conclusion that bodies immersed to a depth of 



6 feet experience less resistance than at the surface ; but in the case of an 



iron plane towed flatwise, he found that resistance increased with the 



depression. 



The whole of these experiments lose much of their value from having 

 been tried on small models, and on bodies which are not ship-shape. 



The ' Philosophical Transactions ' for 1828 contain an account of experi- 

 ments performed by Mr. James "Walker in the East-India Import Dock. A 



