1822.] with Remarks on the Apparatus. 281 



side, but under each other ; and the lower sheave of the block 

 fastened to the top of the mast was smaller, and the uppermost 

 sheave of the lower or movable block was also the smaller. 

 By this arrangement every part of the hne was parallel, and the 

 uncertainty caused by the friction of the line against the sides 

 of the frame avoided. The diameter of each of the larger wheels 

 was ten inches, and that of each of the smaller, seven inches ; 

 and for the sake of hghtness and appearance, they were inserted 

 in iron frames, put together with nuts and screws, for the conve- 

 nience of taking to pieces. A double cylinder would answer the 

 purpose of a system of pulleys ; but so much inaccuracy is 

 caused by the friction of the line in winding as to exclude this 

 contrivance. 



The shape of the conductor represented by figure 14 is prefer- 

 able to any other. The total length 26 feet, each oblique end 

 six feet, the depth one foot, and the breadth one foot nine 

 inches to two feet ; the middle part was excavated within an 

 inch of the bottom, sufficiently capacious to admit a quantity of 

 iron or lead ballast to sink it and its attached body within an 

 inch or somewhat more of the surface of the water. To prevent 

 any alteration in the trim, the water should have access to the 

 hollow by means of small holes, in which the ballast is stowed. 

 The attached body or solid, whose resistance is the object of the 

 experiment, ought to be rendered heavier than water by insert- 

 ing cylinders of lead, so placed that the centre of gravity may 

 be at the place where the bar is inserted. 



Prior to the commencement of each day's experiment, the 

 conductor, with the attached solid, should be weighed ; that is, 

 jis much additional known weight placed on the conductor as 

 will sink it level with the surface of the water. If, on a second 

 day's trial less weight from the absorption of water is requisite 

 to sink it, ballast must be taken out. The conductor is perfo- 

 rated in the middle, and near the commencement of the oblique 

 stern, to admit the bar. A minute alteration when in motion of 

 the horizontal position of the conductor, from the resistance of 

 the water to the under body is made evident, by the water run- 

 ning above the thin edge of the bow or forepart. The edges of 

 the bow and stern should be protected from injury by thin pieces 

 of iron. The correct velocity, or the true resistance, is the latter 

 part of the course ; and after the line which gives motion is (if 

 immersed during the run) above the water. Attention must be 

 paid to this circumstance, or no accurate result can be expected ; 

 for the error will be in the compound ratio of the length and 

 yeJocity of the line which is in contact with the water. 

 I remain, dear Sir, truly yours, 



Mark Beau toy. 



