1882.] 



On Liquid Jets. 



143 



mine coalescence, and that the addition of a small quantity of soap 

 made rebound impossible. Moreover, the " coalescence of the jets 

 would sometimes occur in a capricious manner, without the action of 

 electricity or other apparent cause." 



As in many respects this form of the phenomenon is the most 

 instructive, I was desirous of finding out the explanation of the 

 apparent caprice, and many experiments have been made with this 

 object in view. The observations on fountains recorded in § 1 having 

 suggested the idea that the accidental presence of greasy matter, 

 removable by caustic potash, might operate, this point was examined. 



"July 8, 1880.* — Colliding Jets. — Two large glass bottles, with holes 

 in the sides, close to the bottom, were fitted by means of corks with 

 glass tubes, drawn out to nozzles of about of an inch in diameter. 

 The bottles were well rinsed with caustic potash, to remove any 

 possible traces of grease, and filled with tap water. The colliding jets 

 coalesced in a manner apparently entirely capricious, the only prin- 

 ciple observable being that they coalesced even more readily with high 

 pressures (12 inches) than with low, and with lower pressures would 

 stand collision at greater angles. The addition of caustic potash suffi- 

 cient to give a very decided taste to the water, produced no apparent 

 effect." Subsequently the water used was boiled with caustic potash r 

 but without success. 



"July 27, 28, 29, 30.— On the theory that when the jets collide 

 without uniting there is between them a thin film of air, which would 

 be very liable to be sucked up by water not saturated with air, we 

 tried jets of water through which a stream of atmospheric air had 

 been passed for several hours. We tried it three times. The first 

 time the jets seemed very decidedly less liable to unite capriciously. 

 The second time they behaved even worse than ordinary tap water 

 usually does. The third time we thought it rather better than tap 

 water usually is, but not materially so." 



Jets of hot water, and of mixtures of alcohol and water in various 

 proportions, were also tried at this time, but without obtaining any 

 clue as to the origin of the difficulty. 



I had begun almost to despair of success, when a determined 

 attempt to conjecture in what possible ways one part of the stirred 

 liquid could differ from another part suggested the idea that the 

 anomalies were due to dust. 



" Aug. 1880. — We tried dropping dust on to the colliding jets just 

 above the point of collision, and found that union was always pro- 

 duced. The following powders were tried — powdered cork, sand, 

 lycopodium, plaster of Paris, flowers of sulphur, sugar, dust that had 

 accumulated upon a shelf, and later emery and putty powder. The 

 lycopodium was a little more uncertain in its action than the others, 

 * Mrs. Sidgwick's " Note Boot." 



