1891.] on Some Applications of Photography. 263 



interesting an account last year ; Prof. Rood's multiple discharge 

 was not of that character. It consisted of several detached over- 

 flows of his Leyden jar when charged by the Rhumkorff coil. One 

 number mentioned for the total duration was one six -thousandth 

 part of a second ; but the individual discharges had the degree of 

 instantaneity of which I have spoken. 



It is not a difficult matter to adapt the electrical spark to 

 instantaneous photography. We will put the lantern into its proper 

 position, excite the electric sparks within it, causing them to be con- 

 densed by the condenser of the lantern on to the photographic lens. 

 We will then put the object in front of the lantern-condenser, remove 

 the cap from the lens, expose the plate to the spark when it comes, 

 and thus obtain an instantaneous view of whatever may be going on. 

 I propose to go through the operation of taking such a photograph 

 presently. I will not attempt any of the more difficult things of 

 which I shall speak, but will take a comparatively easy subject, — a 

 stream of bubbles of gas passing up through a liquid. In order that 

 you may see what this looks like when observed in the ordinary way, 

 we have arranged it here for projection upon the screen. [Experi- 

 ment.] The gas issues from the nozzle, and comes up in a stream, 

 but so fast that you cannot fairly see the bubbles. If, however, we 

 take an instantaneous picture, we shall find that the stream is decom- 

 posed into its constituent parts. We arrange the trough of liquid in 

 front of the lantern which contains the spark-making apparatus 

 — [Experiment] — and we will expose a plate, though I hardly 

 expect a good result in a lecture. A photographer's lamp provides 

 some yellow light to enable us to see when other light is excluded. 

 There goes the spark ; the plate is exposed, and the thing is done. 

 We will develop the plate, and see what it is good for; and if it 

 turns out fit to show, we will have it on the screen within the hour. 



In the meantime, we will project on the screen some slides taken 

 in the same way and with the same subject. [Photograph shown.] 

 That is an instantaneous photograph of a stream of bubbles. You 

 see that the bubbles form at the nozzle from the very first moment, 

 contrasting in that respect with the behaviour of jets of water, 

 projected into air. [Fig. 1, Plate I.] 



The latter is our next subject. This is the reservoir from which 

 the water is supplied. It issues from a nozzle of drawn-out glass, 

 and at the moment of issue it consists of a cylindrical body of water. 

 The cylindrical form is unstable, however, and the water rapidly 

 breaks up into drops, which succeed one another so rapidly that they can 

 hardly be detected by ordinary vision. But by means of instantaneous 

 photography the individual drops can be made evident. I will first 

 project the jet itself on the screen, in order that you may appreciate 

 the subject which we shall see presently represented by photography. 

 [Experiment.] Along the first part of its length the jet of water is 

 continuous. After a certain point it breaks into drops, but you 

 cannot see them because of their rapidity. If we act on the jet with 



