S24< M. Breguefs JVew Chronometer for reckoning 
2 Lnits or single seconds upon the segment of a circle op of 60® 
divided into 10 seconds. The larger index m carries at its ex- 
tremity an opaque circular disk, whose centre describes in a 
single second a segment of 60°, which we may also suppose to 
be divided into ten parts or tenths of seconds. The prolonga- 
tions of the divisions 1, S, 5, 7, 9, determine the distances of 
the wires in the field, so that they may give their aid in esti- 
mating the divisions of the scale. The coincidence of the disk 
with one of the wires, or its situation in the middle of one of the 
intervals between the wires, will therefore indicate one, or two, 
or three-tenths. The three needles G, m, ?^, move in the same 
direction as the star in the astronomical telescope. There is a 
detent for stopping the wheelwork, and a lens near the eye for 
enabling it to read off the minutes and the tens of seconds upon 
the dial-plate EF. 
In using this instrument, the observer must notice upon 
the dial-plate EF, the minute and tens ~of seconds, a few 
seconds before the star has arrived at the wires ; then raising 
his eye to the field of the telescope, he will observe by means 
of the shortest needle the units of seconds which are to be 
added. The eye of the observer must now be fixed solely on 
the star which is about to pass behind the first wire, and con- 
tinuing to reckon the seconds, by observing laterally and indi- 
rectly the passage of the disk m over the divisions from 0 to 10. 
As the eye can never be removed for a moment from the star, 
the estimation of the eighteenths of seconds must always be per- 
formed by indirect vision. A little experience will obviously 
be necessary, to enable the practical astronomer to perform this 
operation with facility and confidence ; and it is stated, that the 
instant of the transit of the star by the wire can thus be ob- 
served very distinctly to the tenths of seconds ; — with some prac- 
tice, to the twentieth of a second, and even to some hundredths 
of a second by approximation 
* The particulars from which we have drawn up this notice, are taken from 
the Annates de Ckimie et de Phys., tom. x. p. 431, &c. The interior arrangement 
of the Chronometer, by which an uniform motion is given to the indices, has not 
been described, but is promised by the Editor of that Journal, in a future Number. 
