ADHESION OF PLANE SURFACES. 157 



disks cannot be made to move asunder with a velocity greater tbaa 

 l-64th of that of the blast. Of course all the momentum of the 

 aerial particles which constitute the current through the tube, will 

 be expended on the moveable disk, and the thin ring of air which 

 exists around the orilice between the disks ; and since the movea- 

 ble disk can oidy move with l-64th of the velocity of the blast, the 

 ring of air in the interstice must experience nearly all the momen- 

 tum of the jet ; and must be driven outwards, the blast following 

 it in various currents, radiating from the common centre of the 

 tube and disks. The etlect of such currents in producing an afflujc 

 of the adjoining portions of any tluid in v.hich they may be excited, 

 is well known, having been successfully illustrated by Vcnturi. — 

 See Nicholson's Journal, quarto, vol. ii. p. 172. 



Accordingly the afflux of the air towards the disks counteracts 

 the small velocity which the blast would communicate, and thus 

 prevents their separation, and may even cause them to approach 

 each other, if previously situated a small distance apart. 



This rationale commences with the assumption that the disks 

 will remain nearly parallel. That there cannot be much deviation 

 from parallelism must be evident, since any obiiquity will make the 

 opening greater on one side than on the other ; and the jet pro- 

 ceeding with most force towards the widest opening, will increase 

 the afflux of air upon the outer surface of the moveable disk in the 

 part where the current is strongest, and thus correct the obliquity. 



The phenomenon is advantageously exhibited, when the area of 

 the tube is to that of the disk, as stated ; but were any other ratio, 

 which can be successfully employed, substituted, it would not alter 

 the explanation, [^SiJlima)i^s Journal. 



The phenomenon, described above, and which has excited a 

 good deal of curiosity, was first observed by JVI. Clement, of Paris. 

 He found, that a " flat valve being placed over an orifice in a steam 

 chest, and coveiing a considerable space around the orifice, when 

 the steam was let on the valve, (instead of rising as was expected,) 

 kept its place, and required a considerable additional force to lift 

 it." Some consider Prof. Hare's theory incorrect, and have 

 offered other explanations and experiments, to prove the fallacy of 

 his, and the truth of their own opinions ; they will probably be 

 published in the next number of the Journal, that its readers may 

 judge fof themselves. 



