A Study of Splashes

tching, perhaps half-unconsciously, the thousand little crystal fountains that start up from the surface of pool or river; no

; hoping to share with them some of the delight that I have myself felt, in contemplating the exquisite forms that the camera has revealed, and in watching the progress of a multitude of events, compressed indeed within th

far too rapid to come within reach of any ordinary kinematograph, and even the quickest photographic shutter is also much too slow, so that it is necessary to have recourse to the far shorter exposure of a suitable electric spark. The originals of

he problem to be solved was, therefore, as follows:-To cause a drop of definite size to fall from a definite height in absolute darkness so as to strike the surface of the liquid into which it falls at a spot towards which is directed a photographic camera with un

e same place, and photographed in just the same way, but the flash must now be so timed as to take place at a slightly later stage of the splash, say, one-thousandth of a second later

hotographic plate or film through a distance equal to the breadth of the whole picture every five hundredth or thousandth of a second (if we wish to obtain pictur

actly as required; and (2) that of timing the flash on each occasion within one or

how these two proble

fine glass tube connected to a vessel in which the liquid is maintained at a constant level, as in Fig. 1, or they may be squeezed out slowly as required by means of

g.

g.

tle glass cup such as a deeply concave watch-glass; but other liq

en water or milk will roll over it without sticking, and the drop thus made up will retain a spheroidal form,

(I) and is held in position by means of an electro-magnet (M), against the action of a spring. On cutting off the current from the electro-magnet the spring, acting as a catapult, tosses up the longer arm of the lever and thus removes the watch-glass from below the drop (D), which is left unsupported in mid-air, so that it falls from a de

ead from the outer coats to the dark room, and terminate in a spark-gap (S) between magnesium terminals close over the surface of the water in the bowl just mentioned. If the inner coats are now c

inating spark; we have n

between two terminals S and S connected one to the inside of one jar and one to the inside of the other. These terminals are just too far apart for a spark to

two electro-magnets are on the same electric circuit, so that the drop and timing sphere are released simultaneously. But while the drop always falls the same distance, the height through w

then by raising its releasing-lever about two-fifths of an inch, the laws of falling bodies tell us that we shall postpone

AT

paratus for photo

electrica

se inner coats are connecte

or releasing the

he cat

of iron held down by

sting on the smo

lever against the action of the catapul

towards the liquid L into

esium terminals connected to th

concave

ace close behind it a little concave mirror (R), by means of which a compact beam of rays, which would otherwise have be

rrent is cut off, is not truly instantaneous, and the time required depends on the strength of the magnetizing current and on the temperature of the iron, which in turn will depend on the length of time for whic

AT

to test the accura

ese charges are larger, then the spark will be longer and will take place earlier and before the timing sphere has reached the mid-position. The charging has therefore to be carefully watched by means of the indications of a suitable electrometer, and the timing spher

timing from the photographs given on Plate II, in which a solid sphere was let fall in the dark room past a metre scale. The timing sphere was arranged, in the first four photographs, t

ght-hand edge of the scale. The greatest difference of position being just about one millimetre (as read off the left-hand scale), which would correspond to an error of

e higher up, and it will be seen that if we compare this with No. 3, the error is again only one millime

f the spark, and this image is very much the same in 1, 2 and 4, but much larger and brighter in 3 and 5, showi

oval form, elongated vertically, and a flattened form (see Fig. 4). These oscillations are unavoidable, and their extent will depend partly on the amount of adhesion between the smoked surface and the drop, and as this adhesion is never entirely absent and is variable, depending partly on the length of time that the drop has been lying in the cup, it fo

g.

g.

order to afford the reader an opportunity of judging for himself

millimetres, corresponding to 1/560 of a second. Thus even

2

to test the timing

er or shorter spark is correspondingly less, so that it appears safe to say that the accuracy of the timing was su

of the experiments was to find out what happened, and only incidentally to ascertain exactly how long it took to happen, and there is no doubt that on some occasions, through

g.

e edge of a rapi

The evidence for this is the accompanying photograph (Fig. 5), taken of a cardboard disc when rotating at a rate of fifty-three turns per second; the disc was 22 cm. in diameter, and had been roughly graduated round the edge with pen and ink. The photograph of the part that was in focus shows no perceptible blurring of the edge of the marks, and w

all the photographic processes had to be conducted in absolute darkness. To avoid the tedium of long waiting in the dark room, a light-tight tray was constructed, in which seve

he primary circuit of an induction coil at the surface of mercury was found to

TNO

ave mostly used have bee