222 ON DIVERGING STREAMS 



posing the compressed air at the edge of the 

 aperture, to be an elastic ring of 2f ths diameter, 

 and that every part of this ring shall be struck 

 with equal force from the centre, in a radiating 

 direction to the circumference. By the time 

 that the ring is projected to a sufficient distance 

 to be a diameter of, say 4 inches, it will be 

 stretched from a smaller to a larger circum- 

 ference, and every part of the ring will be equally 

 stretched or attenuated. A part of such a ring 

 may be supposed to be represented in Fig. 7. 

 It is not however necessary that the substance 

 projected should be elastic, for if the ring were 

 made of lead, the effect would be the same; or 

 if grains of sand, or small lead shot, could, in 

 like manner, be thrown from a centre, in all 

 directions around, it is clear that as they were 

 removed farther from the centre, the grains or 

 shot would be more distant from each other, or 

 the stream of them would be more attenuated. 



By a reference to the curve. Fig. 3, repre- 

 senting the degrees of vacuum, it will be seen 

 that the circle of greatest vacuum is near to 

 the aperture ; and it may be inferred, that this 

 fact is opposed to the theory of forced divergence, 

 as on that theory it may be thought that we ought 

 to have the greatest vacuum where the divergence 

 was the greatest, and consequently near to the 



