OF COMPRESSED AIR. 2W 



from a centre, in radiant lines in every direction 

 through enlarging circles, and thus became 

 attenuated as it was thrown off from the centre, 

 in the way that light is diminished according 

 to its distance from its radiating point. For 

 the purpose of ascertaining whether this was a 

 correct view, or not, another experiment was 

 made. 



Instead of a circular valve, one of the form 

 of a cross was used, 6 inches in diameter, of 

 which Fig. 6 is a plan. The centre of this cross 

 valve just covered the aperture B, in Fig. 1. 

 And the four arms /, /, /, /, extended to the 

 diameter of six inches. The four angular spaces 

 between them left on the seat of the valve were 

 covered with pieces of wood m, m, m, w, fitted 

 to the spaces and fastened to the valve seat, 

 leaving the cross valve at liberty, to be raised 

 up between them. By this contrivance, the 

 compressed air, on issuing from the aperture, 

 was confined to four separate streams of equal 

 and uniform breadth, which could not diverge, 

 but passed under the cross until they escaped at 

 the ends of its arms. The tubes with mercury, 

 as in Fig. 1, having been inserted in the aims 

 shewed not more than l-8th of an inch vacuum 

 in any part of the arms, and less towards their 

 outer extremities. And this small vacuum 

 2e2 



