VOL. XXXIX.] PHILOSOPHICAL TKANSACTIONS. 13 



cross containing tlie axis, ggg, bj a pricked circle, denotes a narrow ring of 

 thick blanketing, which (by pressing against the outside case, while it is fixed 

 to the outside of the flat of the wheel) makes the passage into the wheel tight. 

 HHH is another circle of blanketing, likewise fixed to the outside of the wheel, 

 and rubbing against the case ; that the air violently driven against the inner cir- 

 cumference of the case, may have no exit, but at the blowing-pipe at b. 



On the outside of the other flat of the wheel, where the handle is fixed, is 

 a ring of blanketing, like hhh, opposite to it, but none opposite to ggg; be- 

 cause the wood there is not open, but comes home close to the axis. 



Fig. 3 gives a vertical section of the wheel and case, a little forward of the 

 flxis, drawn to a scale twice as large as that of the other two figures. Aa the 

 axis, supported by the irons A, a, cylindrically hollowed, except the upper part, 

 where a pin keeps in the axis, bd the case with the sucking-pipe sa. ea the 

 prop for one end of the axis. 1, 2, the opening into the wheel, gg the emi- 

 nence of the wood, to which is fixed the small ring of blanketing. The four 

 black marks, one of which is near h, represent the sections of the two other 

 rings of blanketing. 



A Calculation of the Velocity of the Air moved by the new-invented Centrifugal 

 Bellotvs, of 7 Feet in Diameter, and 1 Foot thick within. By J. T. Desa 

 guliers, F. R. S. N° 437, P- 44. 



When the wheel revolves on its axis, which is performed in this machine 

 every revolution in about half a second, the air may be considered as divided 

 into as many concentric circumferences, as there are particles of air contained 

 between the least and the greatest circle ; consequently the centrifugal forces 

 will be as the radii, that is, in an arithmetical progression. 



Let R = radius of the greatest circle 3.5 feet, 



r = radius of the least circle O.75, 



m = radius of the middle circle . •• 2. 125 = 4.R -j- ^r, 



t; = the velocity, or space described in a second, "S 



in the middle circle, on the supposition that .2Q.ll, 

 the wheel makes two revolutions in a second j 

 s = space described in a second by the action of 



gravity 



}l6.1. 



* = the space that a particle of air, receding from the centre, would 

 describe in a second, by the action of the centrifugal force at the 

 circumference of the middle circle. 

 Then 2m'.v::v:s\ therefore ^ = «, by Huygens's rule. Let g and c. 



