March 23, 1882] 
NATURE 
495 
vents the instrument approaching too closely to the bed of the 
river, where it might be injured or retarded by obstacles. In 
the interior of the cylinder, c, there is a cylindric case, cy (Figs. 
3, 4, and 5), in which a brass spring is fastened, and through 
which the pin, ¢3, is carried, To this pin the end of the sus- 
pending rope, D, is fastened. The internal diameter of the 
cylinder, C, is a little larger than the outside diameter of the 
hollow rod, a, on which it is to slide. The part, cy, to which 
the rope is attached, is connected with c by an arm which passes 
through a vertical slit in the hollow rod, a. Thus, the instru- 
ment is kept always, if the pipe, A, is properly placed, with its 
axis normal to the plane of the cross section. The cylinder, c, 
is also fitted with rollers, cg cg, which render the motion on the 
fixed rod easy. After the instrument has been placed on the 
rod or staff, a bracket, E (Fig. 1), with a pulley, a, is attached 
at the top, and the rope is carried over this pulley, The 
rope, D, is wound on a barrel, F. This barrel is fixed with 
the frame, A, and the pin, /,, on the arm, G (Figs. 1, 6, and 7), 
which is firmly fastened to the hollow rod, A, With the barrel 
is connected the apparatus, /;, registering the depth at which the 
meter is at any moment. Tbe fan, /,, and gearing, /;, regulate 
the rate of rotation of the barrel and permit the adjustment of 
the speed of the meter in its descent along the rod, A. By the 
handle, 7;, the meter is again raised. The lever, 7, and ratchet 
Fic. 6. 
We 
wheel, /, (Fig. 6), arrest the rotation of the barrel. The movement 
begins ias soon as the ratchet is lifted by the lever. On the 
frame of the barrel, F, are fastened the contact screws, I, 2, 3 
(Figs. 1, 6 and 7), for attaching the wires of the electric circuit, 
The screw, 1, is connected with the rope, D, which is a copper- 
wire rope covered with insulating material. The rope is in 
electric contact with the shaft of the screw through the spring, cg 
(Fig. 5), because an insulated wire, c, (Figs. 5 and 3), connects 
the lower end of the pin, c,, and the loop of one of the screws, 4, 
(Figs. 2 and 3), which fasten the spring to the brass frame, 2. 
The other conductor is the cast-iron pipe, A, which is in contact 
with the rest of the apparatus through the parts c, G, A, 4 and 
F (Figs. 6 and 7). These parts are connected with the screw 2 
(Figs. 1,6, and 7). By putting a wire into the loop of screw 3 
the depth of the meter below the water-line can be registered 
electrically. The registering apparatus, H (Fig. 1), has two 
dials, one marking single revolutions and the other hundreds of 
reyolutions. 
If desired, a recording arrangement can be added, the rota- 
tions of the meter being marked ona slip of paper in the same 
way as ina writing telegraph or chronograph. Prof. Harlacher 
used this arrangement in determining the variation of velocity at 
a given fixed point. The battery, 1, and the clock, or indicator, 
H, with the rod, A, carrying the meter, are placed on a float, P. 
The sight vane, k, is fastened to the rod, A, so that it is parallel 
to the plane of the cross section, and then the axis of the screw 
is normal to the cross section and parallel to the current. The 
float is anchored in large rivers and fastened to guide ropes or 
poles in smaller streams. As soon as the work at one vertical 
of the cross section is finished, the anchor ropes on one side 
are slackened and on the other tightened, so as to bring the 
float into a new position in an easy and a speedy manner. The 
float must be built so as to be capable of supporting four or five 
persons. 
The determination of the mean velocity at one vertical, by 
allowing the meter to slide once from the surface of the stream to 
the bottom, is accomplished thus. The meter, B, and all its 
connections, C, ¢, &c., are brouzht to within a few inches of the 
water surface, the fingers of the electric clock being set to zero, 
Then the barrel, F, is released by the lever, 4, Fig. 6. Assoonas 
the axis of the screw touches the water surface a signal is given, 
the electric clock is brought into the circuit by a spring lever, 
and begins to count the rotations of the screw. It is necessary to 
commence with the meter some small distance above the water 
surface, in order that it may acquire the proper descending velocity 
previous to the counting of therotations. Inacertain number of 
seconds the meter descends from M to N (Fig. 1), having at each 
point in its descent acquired the velocity of rotation corresponding 
to the velocity of the water at that depth. Dividing the number 
of revolutions by the number of seconds the rate of rotation cor- 
responding to the mean velocity at that vertical is found. The 
fact that the disk, q (Figs. 1, 2, and 3), preveuts the meter 
from descending exactly to the bottom entails a small correction, 
This correction, however, will be more insignificant the larger the 
difference of the heights MN and NO, that is, the deeper the river 
in which the observations are made. It is a matter of course 
that the readings of the instrument at each vertical should be 
repeated, and the average of the results taken for the true mean 
velocity. The results of single measurements will not differ 
much from each other, but the repetition of the reading will give 
a certainty that all the variations of the velocity at the given 
vertical are allowed for. 
Before using the meter, its constants must be determined in 
the same manner as with the Woltmann apparatus. A length 
is marked out in a still-water basin, and the meter is frequently 
moved through this distance at different speeds. It is essential 
that the movement of the boat or float on which the meter is 
fixed should be a uniform one. 
The above description of the apparatus will prove that the 
advantages of this form of meter are of considerable importance. 
THE STORAGE OF ENERGY * 
‘THE subject of this lecture has been called by the world at 
large, even by well-informed Punch, ‘‘The Storage of 
Force.” Why, then, have I ventured, in my title, to differ from 
so popular an authority? For this simple reason—that you 
cannot store force any more than you can store time. There is 
as much difference between force and work, as there is between 
a mile and tne speed of a train or between a ship and a voyage. 
Work involves two distinct ideas combined, whereas force only 
involves one, Whena weight rests on the ground, the weight 
pushes the ground down with a certain force, and the ground 
pushes the weight up with the same force, If, then, there were 
such a thing as a storage of force, the mere resting of a weight 
on the ground would be such a storage, since the force exerted 
between the weight and the ground never grows less. But, I 
need hardly say, it would be beyond the ability of the cleverest 
engineer to work a machine, or drive a train, by using a weight 
resting on the ground ; the very expression, ‘‘dead weight,” 
shows how useless it is for the practical purposes of producing 
motion, A weight resting on the safety-valve of a steam-engine 
may be a very good means of adjusting the pressure at which 
the valve shall open and liberate the excess steam, but this 
weight will never work the engine. 
Work is force exerted through space ; if a weight P be raised 
through F feet, P x F foot-pounds of work will be done, and 
there will be a store of P x F foot-pounds of work in the raised 
weight. 
The continuous evaporation of the water from the seas and 
1 Abstract of a lecture delivered at the London Institution on Thursday, 
March 2, by Prof, W. E. Ayrton, F.R.S. 
