Vibrations on Gaseous and Liquid Jets. 387 



split into three, one of the divisions being subdivided; and 

 generally the subdivision occurs at right angles to the plane of 

 the other"*.] 



We have thus far confined our attention to jets of ignited 

 and unignited coal-gas, of carbonic acid, hydrogen, and air. 

 We will now turn to jets of water. And here a series of experi- 

 ments, remarkable for their beauty, have long been known, which 

 claim relationship to those just described. These are the expe- 

 riments of Felix Savart on liquid veins, which have been 

 repeated, verified, and modified in various ways in this place. 

 If the bottom of a vessel containing water be pierced by a 

 circular orifice, the descending liquid vein will exhibit two parts 

 which are unmistakeably distinct. The part of the vein nearest 

 the orifice is steady and limpid, presenting the appearance of a 

 solid glass rod. It decreases in diameter as it descends, reaches 

 a point . of maximum contraction, from which point downwards 

 it appears turbid and unsteady. The course of the vein, more- 

 over, is marked by periodic swellings and contractions. Savart 

 has represented the vein in the manner shown in fig. 17. In 

 this figure a is the orifice end of the vein, the part a n is 

 limpid and steady, while all the part below n is in a state of 

 quivering motion. This lower part of the vein appears continu- 

 ous to the eye ; still, when the finger is passed rapidly across it, 

 it is sometimes not wetted. This, of course, could not be the 

 case if the vein were really continuous. The upper portion of the 

 vein, moreover, intercepts vision ; the lower portion, even when 

 the liquid is mercury, does not. In fact, the vein resolves 

 itself at n into liquid spherules, its apparent continuity being 

 due to the retention of the impressions made by the falling 

 drops upon the retina. If the drops succeed each other in in- 

 tervals of a tenth of a second or less, then, before the impres- 

 sion made by any drop vanishes, it is renewed by its successor, 

 and no rupture of continuity can be observed. If, while look- 

 ing at the disturbed portion of the vein, the head be suddenly 

 lowered, the descending column will be resolved for a moment 

 into separate drops. Perhaps the simplest way of reducing 

 the vein to its constituent spherules is one long ago adopted 

 by myself — namely, to illuminate the vein, in a dark room, 

 by a succession of electric flashes. Every flash reveals the drops 

 as if they were perfectly motionless in the air. 



Could the appearance of the vein illuminated by a single 

 flash be rendered permanent, it would be that represented in 

 fig. 18. And here we find revealed the cause of those swell- 

 ings and contractions which the disturbed portion of the vein 



* The point of departure of these experiments were those of Dr. Young 

 ("Sound and Light," Phil. Trans. 1800). The experiments with the tall 

 smoke-jets were for the most part executed by Mr. Barrett's successor* 



2C2 



