264 The Bight Hon. Lord Bayleigh [Feb. 6, 



a vibrating body, such as a tuning fork, the breaking into drops 

 occurs still earlier, the drops are more regular, and assume a curious 

 periodic appearance, investigated by Savart. I have some photo- 

 graphs of jets of that nature. Taken as described, they do not differ 

 much in appearance from those obtained by Chichester Bell, and by 

 Mr. Boys. We get what we may regard as simply shadows of the 

 jet obtained by instantaneous illumination ; so that these photo- 

 graphs show little more than the outlines of the subject. They 

 show a little more, on account of the lens-like action of the cylinder 

 and of the drops. Here we have an instantaneous view of a jet 

 similar to the one we were looking at just now. [Fig. 2, Plate I.] 

 This is the continuous part ; it gradually ripples itself as it comes 

 along ; the ripj)les increase ; then the contraction becomes a kind of 

 ligament connecting consecutive drops ; the ligament next gives way, 

 and we have the individual drops completely formed. The small 

 points of light are the result of the lens-like action of the droj)S. 

 [Other instantaneous views also shown.] 



The pictures can usually be improved by diffusing somewhat the 

 light of the spark with which they are taken. In front of the 

 ordinary condensing lens of the magic lantern we slide in a piece of 

 ground glass, slightly oiled, and we then get better pictures showing 

 more shading. [Photograph shown.] Here is one done in that way ; 

 you would hardly believe it to be water resolved into drops under the 

 action of a tremor. It looks more like mercury. You will notice the 

 long ligament trying to break up into drops on its own account, but 

 not succeeding. [Fig. 3, Plate I.] 



There is another, with the ligament extremely prolonged. In this 

 case it sometimes gathers itself into two drops. [Fig. 4, Plate I.] 



[A number of photographs showing slight variations were 

 exhibited.] 



The mechanical cause of this breaking into drops is, I need 

 hardly remind you, the surface tension or capillary force of the liquid 

 surface. The elongated cylinder is an unstable form, and tends to 

 become alternately swollen and contracted. In speaking on this 

 subject I have often been embarrassed for wantof an appropriate word 

 to describe the condition in question. But a few days ago, during a 

 biological discussion, I found that there is a recognised, if not a 

 very pleasant, word. The cylindrical jet may be said to become 

 varicose, and the varicosity goes on increasing with time, until 

 eventually it leads to absolute disruption. 



There is another class of unstable jets presenting many points of 

 analogy with the capillary ones, and yet in many respects quite 

 distinct from them. 1 refer to the phenomena of sensitive flames. 

 The flame, however, is not the essential part of the matter, but rather 

 an indicator of what has happened. Any jet of fluid playing into a 

 stationary environment is sensitive, and the most convenient form for 

 our present purpose is a jet of coloured in uncoloured water. In this 

 case we shall use a solution of permanganate of potash playing into 



