14 
MINUTES OF PROCEEDINGS OF 
DESCRIPTION 
of ait 
ELECTRIC CHRONOGRAPH, 
FOB 
THE MEASUREMENT OF MINUTE PORTIONS OF TIME, &c„ 
BY 
LIEUT. II. WATKIN, R.A. 
This chronograph, like several others invented during the last few years, 
makes use of the properties of the induced current of a Ruhmkorff coil; but 
I think differs from them in its extreme simplicity and freedom from minute 
and careful adjustments. 
In this instrument, a weight drops freely in air, and the registration 
(which is entirely effected by the induced spark) does not, as in the Boulenge 
chronograph, commence from the moment of its liberation, but during its 
free fall; thus avoiding any inaccuracies arising from the ever-varying strength 
of the batteries, and the electro-magnets in connection therewith. A great 
advantage also of this arrangement is that any slight error in measuring the 
distance passed over by the weight is of very small importance compared 
to what it would be in those instruments which register from the starting 
point. Thus an error of T i(jth of an inch at the usual point of registration 
in this instrument would represent an error in actual time of only Toiooth 
of a second, in the others of nearly -roWth of a second. Moreover, it will 
register a number of consecutive screens, each registration being in duplicate. 
Erom the fact that the registration takes place during the fall of the 
weight, it is evident that where very minute portions of time are to be 
measured, the experiments may be so arranged that the weight, under the ac¬ 
celerating force of gravity, shall have acquired a considerable velocity before 
the registration commences, and thus any required accuracy obtained. 
Before proceeding to the description, I would remark that the instrument 
here illustrated is an exact representation of the one experimented with; and 
from being altered and added to, from time to time, is not so elegant in 
design as it might be. 
