st notes the hour and minute, and, by pressing
a contact key attached to a flexible cord at the transit instrument,
marks the paper with a letter in Morse telegraph characters,
indicating the hour and minute; he then waits till a micrometer wire
cuts a star and at the instant closes the circuit, so that the second
and fraction of a second are registered on the chronograph paper. When
a set of observations have been taken, the paper is removed from the
cylinder, and the same results are obtained by applying a suitably
divided rule to the marked paper, fractions of a second being
estimated by applying a piece of glass ruled with eleven straight
lines converging to a point. The ends of these lines on the base of
the triangle so formed are equidistant on one edge of the glass, so
that when the first and last lines are so placed as to coincide with
the beginning and end of the markings of a second, that second is
divided into ten equal parts. The base of the triangle is always kept
parallel with the line of dots. The papers, after they have been
examined and the results registered, are kept for reference.

Hipp.

In the astronomical chronograph of Hipp, used in determining
longitudes, the movement of a recording cylinder is regulated by means
of a toothed wheel, the last of a clockwork train, controlled by a
vibrating metal tongue; this important feature is described in detail
in Favarger's work cited above.

Regnault.

_Acoustic Chronographs._--In the chronograph devised by H.V. Regnault
(_Acad. des Sc._, 1868) to determine the velocity of sound propagated
through a great length of pipe, a band of paper 27 mm. wide was
continuously unrolled from a bobbin by means of an electromagnetic
engine. In its passage over a pulley it passed over a smoky lamp
flame, which covered it with a thin deposit of carbon. It next passed
over a cylinder in contact with the style of a tuning-fork kept in
vibration by electromagnets placed on either side of its prongs, the
current being interrupted by the fork; it was also in contact with an
electric signal controlled by a standard clock. Also an
electromagnetic signal marked the beginning and end of a time period.
Thus three markings were registered on the band, viz. the time of the
pendulum, the vibrations of the fork, and the marking of the signal
due to the opening and closing of the current by electrical co