110 Dr. Tj'udail on some Pluenomena of a Water- Jet. 



the time which elapses between the passing of a certain point by 

 one drop and the passing of the same point by the follow ing one, 

 be less than the eighth of a second, the mass will appear conti- 

 nuous. But, on the other hand, with regard to the self-same 

 point, it may be observed that it ought never to appear ob- 

 scm'ed bv the drops thus falling ; for the impression of it must 

 remain upon the eye during the brief space occupied by the drop 

 in passing it, and at every interval between two drops this is 

 renewed. Hence if an object capable of making a strong im- 

 pression be placed stationaiy behind the jet, the said impression 

 ought to be constant. To ascertain if this were the case, I fixed a 

 fine platiniim wire between the poles of a battery composed of four 

 of Bunsen's cells, and shortened the wire imtil an intense white 

 heat was obtained. This was set in a dark room behind the jet 

 and at right angles to it. AMien the portion above the contracted 

 section came between the eye and the Avire, the latter appeared 

 intersected by a dark bar ; but when the portion below the con- 

 tracted section came into this position, the wu-e glow^ed with 

 uninterrupted brightness from end to end, thus proving that the 

 continuity of the mass had ceased. Were the jet illuminated by 

 an instantaneous flash, we ought to see the thing as it actually 

 is for the fraction of time above mentioned. This is effected by 

 the electric spark, which at once disintegrates the jet and reduces 

 it to a string of pellucid beads. 



§4. 



During these experiments a circumstance repeatedly suggested 

 itself, which, although a matter of as common experience as the 

 production of bubbles, has, so far as I am aware of, hitherto 

 escaped notice ; I mean the origin of the sound of agitated 

 water. When the smoke is projected from the lips of a tobacco- 

 smoker, a little explosion usually accompanies each puff; but 

 the nature of this is in a great measure dependent on the state 

 of the lips at the time, w^hether they be diy or moist. The 

 sound appears to be chiefly due to the sudden bursting of the 

 film which connects both lips. If an inflated bladder be jumped 

 upon, it will emit an explosion as loud as a pistol-shot. Sound 

 to some extent always accompanies the sudden liberation of com- 

 pressed air, and this fact is also exhibited in the deportment of 

 our jet. If the surface of the fluid on which it falls intersect its 

 limpid portion, the jet enters silenthj, and no bubbles, as before 

 remarked, are produced. The moment, how-ever, after the bub- 

 bles make their appearance an audible rattle also commences, 

 which becomes louder and louder as the mass of the jet is in- 

 creased. The very nature of the sound pronounces its origin to 

 be the bursting of the bubbles ; and to the same cause the rip- 



