Prof. Magnus's Hydrmdic Researches. 163 



by Savart, these are seldom present in^such quantity as to be 

 especially striking. 



] 20. Even with a perfectly regular flow, it is difficult to esta- 

 blish a quite steady stream ; for if the water flows out under a 

 pressure of about 20 centimetres, it is impossible to ensure the 

 perfect constancy of the jet, even when the '^ tranquilhzer " is 

 used. With a smaller pressure, the jet, it is true, appears 

 perfectly smooth ; but the smallest motion— that, for instance, 

 occasioned by the passage of a carriage in a distant street — is 

 sufficient to displace the image of an object seen by the reflexion 

 from the jet. 



The formation of the swellings. 



121. No swellings, however, are occasioned by such shakings. 

 In order that these may be formed, the vessel from which the 

 water flows must receive regularly and quickly recurring motions. 

 The fittest means for this purpose is furnished by the sounding 

 of a note. Indeed for the production of regular swellings, 

 scarcely any other means is applicable. For, as already remarked, 

 for this eff"ect to be produced, regular and quickly succeeding 

 motions are necessary ; and such always produce the impression 

 of a tone. The effect of such regular vibrations is to cause 

 swellings of about the form shown in fig. 3. The first swelling 

 always lies much nearer to the orifice than does the point where 

 the jet without swellings commences to become turbid. 



122. As is well known, the jet itself occasions a tone, 

 partly because its single separate masses of water set the air, 

 through which they fall, in motion, but especially by the impact 

 of these masses upon some solid or liquid. Hence swelhngs 

 are often produced without the intentional production of a tone. 

 It is only on the prevention of the percussion upon a solid body 

 or upon water which has already flowed out, by allowing the 

 stream to fall upon a board very slightly inclined from the ver- 

 tical, that the note of the jet is too weak to occasion any 

 swellings. 



123. Savart* asserts that if the note which the jet pro- 

 duces by falling through the air, be sounded upon a musical in- 

 strument, swellings are immediately produced, and that these 

 are also formed by the sounding of certain other notes which 

 stand in a simple relation to the first. He asserts, moreover, 

 that, on the contrarj', no such swellings are produced by the 

 sounding of notes which have no such simple relation to the 

 note of the jet itself. My experiments have confirmed this 

 EKiscrtion ; but only for the case where the stream flows out 

 under a jircssure of at least 10 centimetres. If the pressure be 



* hoc. cit. p. 357. 

 M2 



