GENERAL PHENOMENA. 55 



to the resistance of bodies partly immersed in water has been observed, viz. that 

 a boat drawn on a canal with a velocity of more than four or five miles an hour, 

 rises perceptibly out of the water, making the resistance less than if no such effect 

 took place ;" and he further observes, that " theory, although it has never pre- 

 dicted any thing of this nature, now that the fact is proposed for solution, will 

 probably soon be able to account for it on known mechanical principles." 



To observe with accuracy the conditions of some of these discrepant pheno- 

 mena, and reduce to the dominion of known laws certain anomalous facts, so as to 

 obtain a closer approximation to a correct system of theoretical and practical 

 hydrodynamics in those points in which they have hitherto been furthest apart, 

 has been the object of this series of investigations. If the reasoning I have used 

 in the sequel follow accurately from the experiments I have adduced, it will be 

 shewn that there have hitherto been neglected in the calculation from theory of 

 the resistance of fluids to the motion of floating bodies, two important elements of 

 that resistance which affect low velocities by very small quantities, and have 

 therefore escaped observation until certain practical results gave their effects more 

 prominent importance; and that these two elements are, (1.) An emersion of the 

 floating body developing itself as a function of the velocity of the motion, and of 

 the measure of gravitation ; and, (2.) The generation of waves by the motion of 

 the floating body which are propagated in the fluid, and which affect the form of 

 the surface of the fluid, the position of the floating body, and the resistance. 



It appears to me probable that I shall most readily and simply communicate 

 to others the information I have acquired on this subject, by following the order 

 in which I was myself led to the acquisition of it. My examination was first of 

 all directed to the effects produced by motion upon the floating body itself, and 

 afterwards to the motions of the particles of the fluid in which the body is 

 moved. 



Section I. — The Effect 'produced by Motion on the Immersion of a Floating Body. 



It has been suggested as an explanation of the cases in which the motion of a 

 floating body is observed to be facilitated at high velocities, that the moving power 

 by drawing a vessel partially out of the water, so as to diminish its immersion, 

 may lessen the sectional area of resistance of the solid ; and further, that if the 

 moving force be supposed to be applied to the anterior part of a vessel, so as to 

 elevate the prow above the surface of the fluid, the diminished immersion of that 

 part would sufiiciently account for the diminished resistance. These suggestions 

 are not confirmed by observation. The amount of force required to produce the 

 said effect by either of these methods, is found to be more than equivalent to the 

 diminution of resistance produced by such force, and it has been observed on the 



