Grusp— Zime Signals. 41 
The pneumatic system possesses the great advantage of being 
quite independent of any electrical currents in adjacent wires, 
which currents sometimes cause great trouble by producing in- 
duced currents in the electrical wires to the clocks. 
I was at first inclined to recommend this system, but as the 
currents in most of the service wires in the new Institution 
will be, I am informed, constant, and not intermittent, this 
objection does not apply seriously ; besides which, I find, on ex- 
amination of the pneumatic system, as carried out in Paris, 
two serious objections— 
(a). It has apparently been found necessary to transmit the 
power, not by a sudden pulse of air, but by gradually filling the 
whole system of tubes with compressed air, the operation taking 
about 20 seconds, and then allowing this to flow out again during 
40 seconds. Consequently the movement of the clock hand may 
take place anywhere within this 20-seconds period, and this, though 
accurate enough for domestic purposes, would not suffice for some 
of the purposes for which these clocks may be used. 
(0). I find that the air-compressing and distributing apparatus 
is extensive, complicated, and costly for small installations. 'There- 
fore, I do not see my way, at present, to recommend it for this 
particular case, notwithstanding its obvious advantages in other 
ways. 
As regards the electrical system of distribution :— 
There are many excellent systems in the market by which 
pionks, having motive powers of their own in the form of weights, 
springs, &e., can be regulated and cor- 
rected from a central clock, and almost 
any of these, except the sympathetic 
pendulum clocks, would be found suit- 
able. (Fig. 7.) [Tor figs. 1-6, see Plate 
VJ ; 
That which I would prefer is the 
elock which is furnished with a forked 
lever placed over the XII on the dial, 
which lever is momentarily brought 
down, at each hour precisely, by a 
current from the distributing clock, and 
sets the minute-hand right (if it be wrong) by the impact of the 
Fic. 7. 
