On the Electrification of a Steam-jet. 159 



base of the jet, the machine being worked slowly, a startling 

 change instantly comes over the shadow. It becomes dark 

 and dense, at the same time assuming a marked orange-brown 

 tint. By removing the point, or simply connecting it to earth, 

 the shadow can be immediately caused to resume its original 

 appearance, again becoming almost invisible. This operation 

 may be repeated as often as desired, one of the most remark- 

 able things about it being the extreme rapidity with which 

 the changes are produced. 



The point need not necessarily be directed to the origin of 

 the jet ; it is nearly as effective when placed in the steam at 

 a distance of a foot or more from the nozzle ; and in such a 

 case the whole of the steam-jet is equally acted upon from its 

 origin onwards, even when the direction of the point is the 

 same as that of the jet. A ball may be used instead of a 

 point, but it operates only when actually within the jet, 

 whereas a point may be outside it. The effect may also be 

 produced by directing the jet upon an electrified metal disk, 

 supported at a considerable distance from the nozzle. 



I have examined the absorption-spectrum of the steam-jet. 

 When the jet is not electrified, its action upon the spectrum 

 is small, the intensity of the whole being slightly diminished 

 in an apparently equal degree throughout. Possibly the 

 violet is dimmed in a somewhat greater proportion than the 

 other colours. Electrification of the jet causes the violet to 

 disappear completely, while the luminosity of the blue and 

 the more refrangible part of the green is materially decreased. 

 The orange and red are, I believe, quite unaffected. 



From these facts it may be concluded that electrification 

 causes an increase in the size of the water particles contained 

 in the steam-jet. In the unelectrifled condition the majority 

 of these particles are small in relation to a wave-length of 

 light; under the influence of electrification they become larger, 

 and attain a diameter of something like a fifty-thousandth 

 part of an inch. 



The idea naturally suggests itself that the phenomenon 

 may be of the same nature as that observed by Lord Rayleigh 

 in the case of water-jets *. A stream of water issuing in a 

 nearly vertical jet from a small orifice is found to break up 

 into separate drops at a certain distance above the orifice. 

 Under ordinary conditions these drops collide with one 

 another, and, again rebounding, become scattered over a con- 

 siderable space. But when subjected to the influence of an 

 electrified body, as a rubbed stick of sealing-wax, brought 

 near the point of resolution, the colliding drops no longer 

 * Proe. Roy. Soc. 1870. 

 N2 



