Prof. Magnus's Hydraulic Researches. 175 



thin rods. From these thin masses of water, as they separate, 

 small drops appear with great regularity between each two of 

 the greater ones. These small drops are not to be confounded 

 with the much smaller ones which move laterally, and which 

 have been mentioned in the previous paragraph and in § 118. 

 Such laterally-moving drops, it is true, are sometimes produced 

 when the stream has swellings, but only when the note which 

 causes them is impure, or when two inharmonious notes are 

 sounded at the same time. These small drops, which regularly 

 occur between two of the larger drops, and which fall vertically, 

 give the appearance of a hollow cylinder placed in the middle of 

 the swelling, as Savart has already mentioned. They are so 

 small that a change in their form cannot be recognized even by 

 means of the rotating slit. On the other hand, as Savart has 

 also mentioned, the larger drops appear in some places broader 

 than they are long, in others longer than they are broad. At the 

 middle, where a swelling occurs, a spheroid is formed whose ver- 

 tical axis is smaller than its horizontal one. On the contrary, 

 at the point midway between two swellings they appear elongated, 

 so that their vertical axis is greater than their horizontal one. 



160. It follows from Savart's observations*, that by means of 

 the band he employed with alternating light and dark stripes, 

 he only observed the swellings to consist of isolated separate 

 masses. The shape which he gives to the curve in drawing ia 

 rather a deduced than an actually observed one. The greater 

 the credit due to him ! The actual observation by means of the 

 rotating slit is now very simple. 



161. If swellings arc to be formed in a stream, the regularity 

 in the separation of the drops must not only take place in such 

 a manner that all the drops are equally great, but the time which 

 elapses between the formation of two of them must remain con- 

 stant, and the place also at which the drops separate from the 

 stream must remain always the same. For it is only under these 

 conditions that all drops on arriving at the same part of the 

 stream, for instance at the middle of a swelling, are drawn out 

 to the greatest extent in a horizontal direction, and that in the 

 middle between two swellings they are vertically most elongated. 

 It is just on account of their assuming the different diameters 

 always at the same place, that they produce the impression of 

 swellings. 



162. It would be erroneous to suppose that in a jet which 

 does not show any swellings, the separated masses of water do 

 not also change their form in such a manner as to appear at 

 one time elongated, and at another flattened and broad. But 

 these masses are not all of the same size, nor do they separate 



* Ann, lie Ckim. et de Phys. 2ud series, vol. liii. p. 349. 



