82 
Electrical Magazine. 
The problem was this:—to arrange an instrument which 
might indicate and preserve thirty or forty successive obser¬ 
vations, made in very close spaces of time, of a phenomenon 
happening at a greater or less distance from the place where 
the instrument of observation is situated. It naturally oc¬ 
curred to us to employ electricity for this purpose. 
It was furthermore necessary to unite to this physical part 
the mechanical part, which might become very complicated, 
but which, however, was not so much so as the solution in 
question induced us to presume. 
Private reasons had prevented my making this machine 
known ; but, as at present nothing remains to prevent its pub¬ 
licity, I will endeavour to convey as exact an idea of it as I 
possibly Can without the aid of figures ; moreover, it has been 
seen by MM. Arago, llegnault, and Morin, whose authority 
may be quoted if necessary to establish what I advance. M. 
Régnault especially has, so to speak, followed it in ail its 
phases, and has assisted at almost all the experimental essays 
that had in view the verification of the principles on which it 
was established. 
We thought of employing an apparatus with a revolving 
plate, similar to that of M. Morin ; and as we required 
several successive indications distant from each other, we had 
thought of making the style alter its position, by approaching 
or withdrawing from the centre at each new mark ; but this 
means did not appear to us sufficient, in that the marks made 
at the centre and those made at the circumference were not 
within the same limits of error ; for the smaller the radius 
was of the arc traced by the style, the greater would be the 
chance of error. 
We then placed the indications in identical positiom. by 
constructing a cylinder of sufficient length to make foi y or 
fifty distinct observations, all of which should apperta • to 
the same radius. In June, 1843, we commenced the jon- 
struction of our machine, which was not completed until 
May, 1844. 
The following is its arrangement : — 
The apparatus is mounted on a cast-iron frame, and is com¬ 
posed of six distinct parts : — 
1st. Of a system of toothed wheels, set in motion by a cord 
rolled round a cylinder, and to which is suspended the 
moving weight. 
2nd. Of a cylinder, 1 metre (3-28 ft.) in circumference, and 
0*36 metre (T18 ft.) in length, divided on its surface into a 
thousand parts, which are therefore millimetres. In order to 
diminish its friction on the pivots, it is supported by a system