Prof. Magnus's Hydraulic Researches. 165 



swellings were formed even when the fork was held quite close 

 to the stream. If, on the contrary, after being struck, the fork 

 was held upon the stand, swellings immediately appeared, what- 

 ever might be the relation between the note belonging to the 

 jet and that of the fork. 



With small tuning-forks which did not possess either the ori- 

 ginal note of the stream or notes simply related to it, I was 

 unable to produce swellings even when the forks were placed 

 upon the stand. I was equally unsuccessful with an organ-pipe 

 0"63 metre long, which was screwed upon the stand and sounded 

 by means of a distant bellows through a tube. 



It is of course understood that this behaviour only relates to 

 the apparatus mentioned in § 1 17, and which I usually employed. 

 In another instrument less strongly made, swellings were pro- 

 duced by placing on the stand even smaller forks, whose tones 

 were neither the same as, nor simply related to, that of the 

 jet ; and this occurred even when a greater water pressure was 

 employed. 



77^6 swellings are produced by the vibrations of the orifice through 

 ivhich the water fi^ows, and not by the direct action of the undu- 

 lations of the air upon the jet. 



129. It follows from these experiments, that the swellings are 

 chiefly caused by the oscillations imparted to the vessel from 

 which the water flows ; and that, on the contrary, the direct 

 communication through the air of the undulatory motion of the 

 sonorous body acts upon the jet only to a very slight extent, or 

 not at all. 



130. The fact that swellings are occasioned by sounding bodies 

 which give either the same note as, or a harmonic of the note of 

 the jet, and which, being held in the hand, cannot commu- 

 nicate their motion otherwise than through the air, does not 

 prove that the changes are eff"ected directly through the air. For 

 we must not forget that when the peculiar note of the jet is 

 heard, the vessel from which the water flows invariably gives 

 forth a note as well. Hence the peculiar note of the jet is de- 

 pendent upon that which the vessel itself would give ; and the 

 former must stand in some simple relation to the latter. When 

 therefore a note is sounded which is simply related to that of 

 the jet, it must be also simply related to "that of the vessel. 

 Consequently the vibrations of the sounding body, although 

 only propagated througli the air, augment the vibrations of the 

 vessel, and, as will be shown more clearly in the sequel, the form 

 of the jet is thereby changed. 



131. If the note produced by a body held in the hand be suf- 

 ficiently strong, its vibrations are communicated to the vessel 



