respecting Sound and Light. 1 1 1 



this took place, the external curves, which are so constructed 

 as that their ordinates are reciprocally in the subduplicate ratio 

 of the pressure observed in the second cavity, with apertures 

 equal in semidiameter to their initial ordinate, approach, for a 

 short distance, nearer to the axis than the internal curve : after 

 this, they continue their course very near to this curve. Hence 

 it appears, that no observable part of the motion diverged 

 beyond the limits of the solid which would be formed by the 

 revolution of the internal curve, which is seldom inclined to 

 the axis in an angle so great as ten degrees. A similar conclu- 

 sion may be made, from observing the flame of a candle sub- 

 jected to the action of a blowpipe : there is no divergency 

 beyond the narrow limits of the current; the flame, on the con- 

 trary, is every where forced by the ambient air towards the 

 current, to supply the place of that which it has carried away 

 by its friction. The lateral communication of motion, very 

 ingeniously and accurately observed in water by Professor Ven- 

 ture is exactly similar to the motion here shown to take place 

 in air ; and these experiments fully justify him in rejecting the 

 tenacity of water as its cause : no doubt it arises from the rela- 

 tive situation of the particles of the fluid, in the line of the cur- 

 rent, to that of the particles in the contiguous strata, which is 

 such as naturally to lead to a communication of motion nearly 

 in a parallel direction ; and this may properly be termed friction. 

 The lateral pressure which urges the flame of a candle towards 

 the stream of air from a blowpipe, is probably exactly similar 

 to that pressure which causes the inflection of a current of air 

 near an obstacle. Mark the dimple which a slender stream of 

 air makes on the surface of water ; bring a convex body into 

 contact with the side of the stream, and the place of the dimple 



