[ 68 ] 



principle by which we accounted for the augmentation of the- 

 diameter of a vertical vein of water, through a limple orifice, 

 when the velocity of the effluj: is confiderable. For when a per- 

 pendicular pipe is inferted, the velocity of the difcharge being 

 confiderably encreafed, the refiftance from the air will be fo like- 

 wife; and thus the diameter of the vein has a tendency to en- 

 large itfelf; now in the widening cone, the pipe admits of this 

 augmentation, at the fame time that it encreafes the velocity; but 

 the cyHndrical pipe, though it equally encreafes the velocity, yet 

 it does not permit the vein to enlarge itfelf, and by thus con- 

 fining it, the efflux is obflruded, and the quantity difcharged in 

 a given time is diminiflied. Accordingly, under the receiver of 

 an air-pump, even in a moderate degree of exhauflion, there is 

 no difference perceived between the velocities with which a fluid 

 is difcharged through a conical or cylindrical pipe. 



