Prof. Magnus on the Motion of Fluids. 21 



CC is a wooden cistern or barrel, rendered air-tight ; the tubes 

 AA widen towards the top ; two boards, pp, inchued to\yards 

 each other, are introduced above into each tube, thus forming a 

 funnel-shaped narrowing of the orifice; the boards are kept 

 asunder by the pieces of wood it. 



Below these pieces a number of apertures, ee, are made in the 

 tube, through which air can enter. Similar apertures, e'e', were 

 made in Richard's instrument about half-w^ay up the tubes ; from 

 these water sometimes escapes, as Richard himself has found ; 

 and for this reason it would be better to omit them altogether. 



"When the conical stopper k of the funnel-shaped orifice pp 

 is drawn upwards, the water falls through the tube, and at the 

 same time air is sucked in at the orifices ee* ; as this is carried 

 do\^Tiwards by the water into the cistern, the air in the latter 

 increases, and passing into the tube H, streams out of the 

 opening b. 



At q, in the bottom of the chest CC, an opening is made 

 through which the descending water can escape. The magnitude 

 of the opening is so arranged that the water can never sink down 

 to it. A second trough is generally placed before the opening, 

 in which the water must first ascend to escape over the edge. 



Notwithstanding all that has been written about these bel- 

 lows f, which in some departments in the south of France have 

 been variously applied, and however comprehensive and exact 

 the description given by Richard in the w^ork already mentioned, 

 which appeared in Paris in 1838, the real physical cause of the 

 descent of the air is still totally imknown. 



Richard has not at all entered upon this subject, ximong 

 the old writers, Justi J asserted in the last century that the water 

 is changed by the violent motion into air. Venturi§, in 1800, 

 referred the origin of the bubbles to the lateral motion imparted 

 to the air by the moving stream. This would imply that a force 

 of attraction exists between the air and water sufficient to carry 

 the former far beneath the surface, which, as already remarked 

 in § 16, is scarcely conceivable. Besides, at the place men- 

 tioned an experiment is described which I believe entirely refutes 

 this notion. 



In order, however, to observe with more exactness the action 



* Instead of sucking in the air through the apertures ee, there is another 

 arrangement, where, in place of the hoards pp, two wooden funnels are used, 

 which are high enough to reach over the surface of the water. The water 

 flows through the space between the funnels ; this causes the fluid within 

 them to sink and the air to enter. 



t These bello^\•s are chiefly used in the immediate extraction of iron from 

 its ores {Forces caialanes) ; and acciu'tUng to Richard, they were used in 

 1838, with one or two exceptions, in all the works in the Departcment 

 de I'Ariege. 



X Exhibition of Arts and Manufactures, vol. ii. p. 97, note. 



§ Gilbert's Annalen, vol. iii. p. 12^. 



