132 



Lord Rayleigh. 



[June 15, 



reduced to below yoo inch, the scattering cannot be completely 

 prevented by the presentation of an electrified body. One possible 

 reason for this is evident. The mutual repulsion of the similarly 

 electrified drops increases rapidly relatively to the masses as the 

 size is reduced, and thus it may happen that before the differential 

 electrification sufficient to rupture the separating envelope at 

 contact is arrived at, the repulsion may be powerful enough to 

 prevent most of the drops from coming into contact at all. In 

 connexion with this it may be remarked that two perfectly equal 

 and equally electrified spheres would repel one another at all dis- 

 tances ; but that if there be the slightest difference in the size or 

 electrification, the repulsion will be exchanged for attraction before 

 actual contact is attained. This attraction will be local, and thus the 

 opposed parts of the surfaces may come into contact with considerable 

 violence, even when the relative motion of the centres of the masses 

 is small. It is easily shown experimentally (see § 4) that violence 

 of contact tends to promote coalescence, so that we have here a 

 possible explanation of the action of electricity. 



With respect to the persistent scattering of very fine jets, however, 

 it would appear that the principal cause is simply that many of the 

 fine drops fail to come into contact in any case. The capillary forces 

 act with exaggerated power, and doubtless impress upon the minute 

 drops irregular lateral velocities, which may easily reach a magnitude 

 sufficient to cause them to clear one another as they pass. At any 

 rate little difference is observable in this respect between a fine jet of 

 clean water under feeble electrical influence, and one to which a little 

 milk has been added, bat without electrification. 



With a suitable jet, say from a nozzle about inch diameter, and 

 rising about 2 feet, the sensitiveness to electricity is wonderf ul, more 

 especially when we remember that the effect is differential. I have 

 often caused a jet to appear coherent, by holding near the place of 

 resolution a brass ball about 1 inch in diameter, supported by a silk 

 thread, and charged so feebly that a delicate gold-leaf electroscope 

 would show nothing. Indeed, some care is necessary to avoid being 

 misled by accidental electrifications. On one occasion the approach 

 of a person, who had not purposely being doing anything electrical, 

 invariably caused a transformation in the appearance of the jet. 



The jets hitherto under discussion are such as resolve themselves 

 naturally into drops soon after leaving the nozzle, or at any rate 

 before approaching the summit of their path. If the diameter be 

 increased, we may arrive at a condition of things in which the undis- 

 turbed jet passes the summit unbroken. In such a case the addition 

 of milk, or the presentation of an electrified body, produces no 

 special effect. One interesting observation, however, may be made. 

 By the action of a vibrator of suitable pitch, e.g., a tuning-fork, 



