284 
POPULAR SCIENCE REVIEW. 
1. For E. M. F. to arise in a free jet, the water must he in contact with 
a solid body. 
2. E. M. F. is only evolved where the particles of fluid undergo friction, 
so that only a small part of the jet contributes to its development. 
3. When the velocity of the jet is altered, the E. M. F. is proportional 
to the vis viva of the particles. 
4. The E. M. F. varies with the nature of the bodies in contact. 
From which observations he concludes : That (a) motion of a fluid by itself 
does not produce E. M. F. (/3) Capillary currents are conditioned solely by 
friction of particles ; in those which do not wet the wall of the tube, by 
friction against this ; in those which do wet it, by friction against a layer of 
fluid condensed against the wall, (y) Capillaiy currents are identical with 
the friction currents appearing in the rubber of an electrical machine. 
The Acceleration of Gravity for Tokio, Japan, formed the subject of a 
paper read before the Physical Society by Messrs. Ayrton and Perry. They 
proceeded by the following method : — A brass ball, 2352 # 2 grammes in 
weight, was suspended by a long steel wire O' 45 millimetre in thickness, and 
in the earlier experiments 978*7 centimetres in length. The wire was sup- 
ported from a steel knife-edge resting on a brass plate. Both the brass ball 
and the bob of the seconds-pendulum of the standard clock were fitted with 
fine pieces of platinum wire, either of which dipped into a small cup of mercury 
when the pendulum to which it was attached was vertical. The mercury- 
cups, &c., were then joined up with a battery and resistance-coils to a quick- 
running Morse instrument. The whole constituted what is known as a 
1 break-circuit chronograph/ that is, a continuous ink-mark was made on the 
paper run out by clockwork, broken by a very small gap each time the wire 
attached to the bob of the seconds-pendulum passed through the mercury. 
These breaks, then, in the ink line indicated seconds ; if, however, both pen- 
dulums were simultaneously in the vertical line, no break was made. Hence 
the absence of a break in the line at the end of any special second indicated 
coincidence of the two pendulums ; and in this way the times of a large 
number of coincidences could be automatically registered. 
During this set of experiments they could not measure the long fine steel 
wire with as much accuracy as was desired, since, although they had two or 
three brass scales, the makers had omitted to record on them at what 
temperature they were correct. However, assuming that one of them was 
accurate at 0° C., then a rather large number of experiments gave, as the 
value of g, 978'8 centimetres per second as a first rough approximation. 
Subsequently they obtained from the Finance Department of Japan the 
loan of two very beautiful brass scales, by Deleuil of Paris, and guaranteed 
correct at 0° C. One was graduated in millimetres ; the other consisted of a 
brass rod, with two pieces at its ends at right angles to the rod, and the 
distance between the two planes of the inner surfaces of the pieces was 
exactly a metre at 0° C. They had, then, the means of making a far 
more complete series of experiments than before ; but as their trial pendulum 
was nearly ten times as long as the seconds-pendulum of their clock, the 
method of coincidences was an inconvenient one; and so they merely 
adopted the following : — The long pendulum alone controlled the ‘ break-circuit 
chronograph ; ’ so that the number of breaks in the line during any time 
