ON NA VA L A RCIII TEC TURE. 299 



I have to say, but I will endeavour to inalic it as clear as I can, and I 

 will only ask you to bear in mind that the attempt to be brief generally 

 leads to some obscurity. 



I \vill divide what I have to Gay into three portions. I will tell you, first, 

 what it is I am doing ; secondly, a3 well as I can 1 will explain what is the 

 justification of the mode of procedure in U3ing models to test the forms 

 of ships ; and, thirdly, I will give you some slight sketch of the result 

 that we have obtained and arc obtaining. The thing to be clone is, to 

 determine by measuring the resistances of a model at various speeds, 

 what will be the resistances of a ship similar to the model at various 

 speeds, and for convenience I will in the first instance give you a, term, 

 which is very serviceable in reference to this subject, the term, 

 namely, which expresses the form in which we embody the ascertained 

 merits of the model or ship as a body moving with greater or less 

 resistance. We reduce the results obtained from each form, to 

 what we call a "curve cf resistance." \Ve introduced that term be- 

 cause it is a short expression and means a good deal. On a straight 

 base line are set off a series of speeds beginning with zero, and going on 

 to one, two, three, &c., in units of speed, whatever they may be. For 

 every speed for which the resistance is ascertained, the resistance is set 

 off a to scale, and is plotted as an ordinate on the base line at the appro- 

 priate speed. Having thus obtained a series of ordinates representing 

 thj resistances, a curve drawn through their summits constitutes the 

 curve of resistance. That curve expresses the resistance which the 

 model or ship will experience at any intermediate speed. In speaking 

 of the resistance of a mode!, I shall generally speak of its curve of 

 resistance as expressing this. 



The object, then, is by the use of models to determine the curves of 

 resistance for ships, and in order to do that with effect, it is necessary to 

 be able to produce models, lapidiv, economically, and exactly. For 

 this purpose it was necessary to find some more suitable material than 

 wood. It is well known that to make a large exact model in wood, 

 occupies considerable time, requires skilled labour, and costs a great 

 deal ; but happily a rather new material in organic chemistry, paraffin, 

 so called because it has little affinity for anything else opportunely 

 presented itself, and by the use ^f this material we are able if we please 

 to complete a model sixteen feet long, cf the general dimensions of 



