ON THE VELOCITY OF A VESSEL. 367 



tinued ; which renders the problem more difficult. If we suppose 

 this angle to be 15 degrees, which Bouguer considers as near the 

 truth, it will be found that the angle in question ought to be 46 

 degrees 40 minutes. 



Ships do not receive the whole benefit of this force ; for the 

 length of the tiller does not permit the helm to form with the keel 

 an angle of more than 30 degrees. 



[Hutton. Montuclcfs Ozanam.] 



SECTION x. 



On the Velocity of a Vessel compared witk that of the Wind. 



A VESSEL can never acquire a velocity greater than, or even 

 equal to, that of the wind, when in a direct course, or when she is 

 sailing before the wind ; for besides that in this case a part of the 

 sails injure or intercept the rest, it is evident that if the vessel should 

 by any means acquire a velocity equal to that of the wind, it would 

 no longer receive from it any impulse ; its velocity then would begin 

 to slacken in consequence of the resistance of the water, until the 

 wind should make an impression on the sails equal to that resist- 

 ance, and then the vessel would continue to move in an uniform 

 manner, without any acceleration, with a velocity less than that of 

 the wind. 



But, when the course of the vessel is in a direction oblique to that 

 of the wind, this is not the case. Whatever may be its velocity, the 

 sail is then continually receiving an impulse from the wind, which 

 still approaches more to equality, as the course approaches a direc. 

 tion perpendicular to that of the wind : therefore, however fast the 

 vessel advances, it may continually receive from the wind a new im- 

 pulse to motion, capable of increasing its velocity to a degree supe- 

 rior to that even of the wind itself. 



But for this purpose it is necessary that the construction of the 

 vessel should be of such a nature, that, with the same quantity of 

 sail, it can assume a velocity equal to 8-llths or 3-4ths that of the 

 wind. This is not impossible, if all the canvas which a vessel can 

 spread to the wind, in an oblique course, were exposed in one sail 

 in a direct course. This then being supposed, Bouguer shews, that 

 if the sails be set in such a manner, as to make with the keel an 

 angle of about fifteen degrees, and if they receive the wind in a per. 



