Nipher — Frictional Effect of Railway Trains upon the Air. 225 



as calms and gusts of wind alternate with each other. In a 

 timbered region, or along the banks of the Mississippi river, 

 where the bluffs and timber check the air current, the phe- 

 nomenon is always present. The locality where James 

 Graney was killed was eminently favorable to the production 

 of train draught, even with a transverse wind. 



The effect of a wind blowing against any object, is the re- 

 sult of the compression on the windward side and the rare- 

 faction on the leeward side. The cup-shaped collector used 

 in these measurements, gives only the compression. The 

 effective pressures acting on any object like a pressure board, 

 are about thirty-three per cent, greater than those computed 

 by Newton's formula.* 



* These Transactions, Vol. VIII, No. 1, p. 19. 



