THE EXPERIMENTS OF 1836. 95 



PART III. 



The investigations of 1834 had established the principal points in the rela- 

 tion between the resistance of a fluid, the diminished immersion, and the velocity 

 of the wave. The prominent features in the representation of the law had been 

 traced, but the outline being in many parts faintly and ambiguously given, re- 

 quired to be retouched, corrected, and filled in. The power of horses, which 

 had been used as the moving force, was desultory in its action, so that the mea- 

 sure of the force employed did not always afford the means of obtaining even a 

 tolerable approximation to an accurate measure of resistance at a uniform velo- 

 city. Yet the power of horses had this advantage, that it could be continued for 

 a much greater length of time, and over a much longer space, than that obtained 

 by the action of a falling weight, or any other convenient mechanical means. For 

 small models, indeed, it would have been sufficiently simple to provide, as has 

 frequently been done, the means of applying a continuous moving force ; but I was 

 not, in 1834, in possession of any plan by which this object could be accomplished, 

 so as to obtain a continuous moving power, acting through a great space, to ge- 

 nerate high velocities in vessels of large size carrying considerable weights. In 

 1835, I had, however, attained this desideratum. 



The means of obtaining the continuous action of a moving force with great 

 power and through a great space, were very simply and conveniently obtained ; 

 and as the method may be useful to other inquirers, I shall on that account de- 

 scribe it more particularly than might perhaps be necessary for the mere purpose 

 of appreciating the experiments conducted with it. The method which has been 

 previously used for obtaining the power by means of a weight, has been by sus- 

 pending that weight from an elevated structure by strands of rope passing over 

 pulleys, by which a given weight, in falling through a given space, acts through 

 one of the strands so as to move the end of the rope through a space greater than 

 the space through which it falls by as much as the number of strands exceeds 

 unity. In this case the weight to be raised, in order to obtain a given power, in- 

 creases so rapidly with the increase of the space and the friction of the pulleys, 

 and the effect of rigidity increases so rapidly along with it, that the limit of 

 practicability, and, at all events of inconvenience, is very soon attained. Fur- 

 ther, after one experiment has been obtained by an apparatus of this kind, con- 

 siderable time must elapse before the we'ght is again elevated, and the rope dravni 

 out to its former station for commencing another experiment. In the method 

 which I have adopted, the weight never requires to exceed twice the moving force 

 required, plus friction and rigidity, for five pulleys ; the weight requires no increase 

 for the space moved over, except for the friction of the additional horizontal 



