42 Scientific Prececdings, Royal Dublin Society. 
A-shaped fork against a pin on the minute-hand. ‘This is simple, 
inexpensive, and very reliable. 
Any clock of this form, however, requires winding periodi- 
cally; and if it be desired to avoid this, one or other of the second — 
class of electric clocks which do not require winding must be used- 
There are many varieties of these also in the market, but I 
cannot say that any of them are certain to prove satisfactory. 
It is much more difficult to keep a clock going correctly when it 
has no driving power of its own, and when the work of driving, as 
well as regulating, has to be done by the electric current. 
There are some excellent clocks of this description in‘ the 
market, but if must be remembered that there is one great differ- 
ence between the working of these driven clocks and that of the 
first-mentioned clocks, in which the regulation only, and not the 
driving, is effected by the electrical current. 
In the latter, if the current at any hour fails from some cause 
to do its duty (and in electrical arrangements of the very best 
order this will sometimes happen), the only result is that, at the 
next hour, the correction to be made will be double that which 
would have been required if the former current had acted rightly ;. 
and the error in the clock before that correction will be double 
that which it would have been for the one hour; but as the 
error for two or three hours run must be very small, and as 
it is wiped out completely by the first current that comes after the 
Juilure, this is of little consequence. 
In the former case, however (that of the driven clock), any 
error that occurs is not wiped out by any of the succeeding cur- 
rents, but remains there until set right by human agency; and 
if the errors, though only occasional, be (as is likely). mostly of 
the same character, ¢.e., gaining or losing, they will accumulate, 
and in time amount to a serious quantity. 
For the above reasons I would recommend for this purpose, 
where convenient, the adoption of clocks which have a motive 
power of their own, and which only depend on the central clock 
for periodic correction of any accumulating errors; or if, as is. 
sometimes the case, it is highly desirous to avoid the necessity 
of periodic winding, clocks of the self-winding principle may 
be used, corrected periodically from the central or distributing 
clock. 
