212 EIGHTH REPORT — 1838. 



1100 yards was 172 seconds, and that therefore the mean ve- 

 locity of the descent was 19* 18 feet per second. But by com- 

 paring the times of descending each successive interval of 110 

 yards, it will be observed that the rate of acceleration, instead 

 of being uniform, as it would be independently of the resistance 

 of the air, is gradually less ; and the last 330 yards of the plane 

 was descended at an uniform velocity of 33 feet per second. 



Mr. Woods has computed the value of /. determined by the 

 formula 10, page 207, for the first 110 yards, the first 220 yards, 

 the first 330 yards, and the first 440 yards, and the following 

 are the results. 



1. From to 110 yards /= -00228 = 5'107 pounds per ton. 



2. FromO to 220 yards/ = '00255 = 5*712 pounds per ton. 



3. FromO to 330 yards/= -00265 = 5-936 pounds per ton. 



4. From to 440 yards/ = -00293 = 6-563 pounds per ton. 



The increasing value of/ shows the increase of the resistance 

 with the velocity. In the first 110 yards, the mean velocity 

 being only 6-34 feet per second, the resistance of the atmosphere 

 was trifling, and the value of/ may be considered as a close ap- 

 proximation to the friction, properly so called. 



Since in the first 110 yards there must have been some atmo- 

 spheric resistance, however small, it follows that the friction, 

 properly so called, must have been less than the value of / ob- 

 tained by Mr. Woods' calculation. We shall therefore assume 

 that /was in this case less than 5-11 pounds per ton. The total 

 amount of friction, therefore, for the load of 25-58 tons would 

 be less than 130-7 pounds. If we take the mean resistance of 

 this load at 9-17 pounds per ton, as determined by M. de Pam-- 

 hour's method, we shall find the total mean resistance to be 

 234-55 pounds. The mean atmospheric resistance would there- 

 fore be greater than 104 pounds. 



It will be observed that this result is in accordance with that 

 already obtained for the load of 31-31 tons, by a different process 

 of reasoning. The determination of the limit of /, by the for- 

 mula (10.), may, however, be regarded as a closer approximation. 



The angle of friction corresponding to 5-11 pounds per ton, 



would be 1 in 438. Therefore /< — -• 



438 



We shall not pursue these experiments of M. de Pambour 

 further than to observe, that the computed resistances of the 

 single wagons, as given in p. 209, rendered the eff"ects of the 

 resistance of the air still more apparent. While the mean 

 computed resistance of the train of five wagons was only 8*69 

 lbs. per ton, their gross weight being 31-31 tons, that of the 



