1822.] loith Remarks on the Apparatus. 279 



ing the after extremity. The experiments made with these 

 bodies, 3 and 4, are contained in Table 4, and show, hke the 

 former, a considerable increase of resistance. The minus pres- 

 sm-e found by these last experiments is set down in Table 2. 

 The minus pressure thus ascertained rests on the supposition 

 that a wedge whose obhque sides exceeds the width of the base 

 four times and a half is devoid of that kind of resistance. To 

 . clear up any doubts on this subject, experiments were made with 

 bodies 5, 6", 7, ^, 9, 10; the stern ends of solids 6, 8, 10, were- 

 shorter than those of 5, 7, 9; the obhque sides of these mea- 

 sured in length three feet, and the obhque sides of the others 

 four feet and one half. Tables 5, (5, and 1, contain the experi- 

 ments, with these figures, and justify the conclusion that the 

 minus pressure of those sohds that have the longest after extre- 

 mity is so minute that it may be considered as nothing, and 

 consequently rejected. 



By consulting Tables 3 and 4, it might be concluded that of 

 all the variety of forms of whicli the stern end is susceptible, the 

 most obtuse would have the greatest minus pressure. To prove 

 or disprove the justness of this inference, the resistance of solids 

 11, 12, 13, were found, the last being the same as figure 2, that 

 is, with a square stern. Fig. 12 is the same as fig. 8, turned 

 end for end, or the hind part made the bow and vice versa ; but 

 the stern of fig. 11 is an equilateral triangle. The result of these 

 experiments is set down in Table 10, and it is very singular that 

 an equilateral triangle so far from diminishing the minus pres- 

 sure; augments it ; and, on the contrary, a semicircular after 

 body diminishes the minus pressure. The effect of joining an 

 equilateral triangle to the base of an isosceles considerably 

 augmented the resistance near the surface, as will appear iioni 

 the following experiments : A wedge 43 feet in length, 4-75 feet 

 in width, -and 1,28 feet in depth, and nearly immersed, required 

 a motive weight of 395,} pounds to draw it 12 feet in a second 

 through the water by the vertex. On the addition of an equila^ 

 teral triangle to produce the same velocity, 470 pounds were, 

 requisite, being an increase of 74-|- pounds. That the shape as 

 well as length contributed to diminish the negative pressure 

 appears by comparing the result of fig. 12 with fig. 11, as con-, 

 tained in Table 8. The minus pressure of fig. 9 being nothing, 

 it might be expected that the plus pressure or head resistance of 

 this figure would be the same as the weight of water contained 

 in Column 3 of Table 2 ; but on examining Table 2, the head 

 resistance is smaller ; consequently the plus pressure increases 

 in a less ratio than the squares of the velocity. 



Some observations on the size of the bodies, and the difficul- 

 ties experienced in making the experiments, may not prove 

 unacceptable to those who hereafter engage in a similar employ- 

 ment. It is recommended that the size of the bodies whose 

 resistance is to be determined, should, if square, not exceed one 



4 



