VOL. XLVIIi:j PHILOSOPHICAL TRANSACTIONS. 457 



being thus cominunicated to a spindle within the ship, this spindle may be made 

 to drive a set of wheel-work, which will register the turns of the y ; and the 

 value of a certain number of these turns being once found, by proper experi- 

 ments, they are easily reducible into leagues and degrees, &c. The only diffi- 

 culty then is, whether this y will make the same number of rotations in going 

 the same space, when it is carried through the water fast, as when it is carried 

 slow. On this head Mr. de Saumarez, as well in the paper above-cited, as in a 

 subsequent one published in Philos. Trans. N° 408, has given an account of 

 several trials, which he has made of it, from which it appears, that this machine 

 in part answers the end proposed, and is in part defective; the errors of which 

 he supposes to proceed from the sinking down of the y into the water on a slow 

 motion ; the axis of its rotation being then more oblique to the horizon, than in 

 a quick one. 



In a machine constructed like this, it is evident that the end of the spindle, to 

 which the rope is fastened, must be of sufficient strength and thickness, not only 

 to bear the force or stress, that the hauling of the y through the water will lay 

 on it, in the greatest motion of a ship; but also to bear the accidental jerks of 

 the waves. The thickness of the spindle then being determined by these con- 

 ditions; it is also manifest, that to prevent the spindle from being pulled out of 

 its place by the draft of the rope, there must be a shoulder formed on it, which 

 must be greater than the part of the spindle before described, for the spindle to 

 bear against. The size that Mr. Saumarez proposes to give to his y, is 1^ inches 

 tfie whole length; 15 inches for the length of the arms, which are to be opened 

 to a right angle; 8 inches for the length of each vane; A\ inches broad, and^ 

 the stems and shank to be \ of an inch thick. According to these dimensions, 

 the resistance that this part of the machine will meet with, in passing through 

 the water, will, in the swift motions of the ship, be very considerable; conse- 

 quently the necessary bulk of the pivot-end of the spindle, and its shoulder, will 

 occasion a considerable friction in its turning, and retardation to the rotation of 

 the machine. 



To cure these defects, as much as possible, instead of the y before described, 

 Mr. S. made trial of a single plate of brass, of about 10 inches long, 2-J- broad, 

 -^ of an inch thick, and cut into an oval shape. This plate being set a little 

 atwist, and fastened by one end to a small cord, in the manner of the y, is like- 

 wise capable of making a rotation, in being drawn through the water; but with 

 this diffiirence, that as this is but a small thin plate drawn edgewise through the 

 water, its resistance, in passing through it, is much less; of consequence, a 

 much smaller line is sufficient to hold it, which again considerably diminishes 

 the resistance; and this of course proves a double diminution of friction in the 

 spindle; first, as the pressure upon it is less; and, secondly, as it allows the 



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