256 Mr. Tredgold on a new Theory of the Resistance 



elude that the formula is sufficiently uear for any practical 

 purpose, as far as this species of body is concerned. 



23. Some experiments were made in a very different man- 

 ner by Mr. Vince*, and besides being chiefly made with thin 

 planes, they were made by a rotary machine, which rendered 

 it necessary to determine the centre of resistance. This he 

 has done inaccurately ; but neglecting its effect on the results, 

 the experiments give the ratio of the height due to the resist- 

 ance to be to the height due to the velocity as 3 : 2. This is 

 the same as the ratio we have derived from theory (Art. 9.). 



The experiments with a thin plane set at different angles 



may be compared with the equation — (2 sin 2 a + sin fl) = H; 

 (Art. 12.) which making the resistance at 90° equal 1000, will 



vary as lOOO (2 sin * a + sin a) 



3 - 



Mr. Vince also tried the resistance of hemispheres moving 

 in water; with the base foremost, and with the spherical side 

 foremost, the ratio was 8339 to 3400. The resistance of a 

 cylinder of the same diameter he found to be 7998; hence 

 making the latter unity we have By experiment ; Cylinder 1 ; 

 base of hemisphere 1*05 ; round side *427. 

 By calculation ; Cylinder 1 ; base of hem. *835, round side *6. 



24. The experiments of Dubuatf on the pressure of water 

 on bodies moving in it tend to confirm the relation of 2 to 1 

 between the direct and minus pressure of a column capable of 

 generating the velocity. He has shown that the pressure is 

 different on different parts of a plane surface, and this we might 

 expect ; but the whole effect is not altered by the distribution 



* Phil. Trans. Abrid., vol. xviii. p. 250. 



f Principes (V ' Hydraulique, torn. ii. partie 3. 



of 



