American Horological Journal, Vol. I, No. 1, July 1869: Devoted to Pratical Horology

Vol. I.NEW YORK, JULY, 1869. No. 1.
⁂ Address all communications for Horological Journal to G. B. Miller, P. O. Box 6715, New York City. Publication Office 229 Broadway.
However accurate an instrument for the mensuration of time may be, it would be of little use for close observation unless we have some standard by which to test its performance. We look to Astronomy to furnish us with this desideratum, nor do we look in vain. The mean sidereal day, measured by the time elapsed between any two consecutive transits of any star at the same meridian, and the mean sidereal year—which is the time included between two consecutive returns of the sun to the same star—are immutable units with which all great periods of time are compared; the oscillations of an isochronous pendulum affording us a means of correctly dividing the intermediate space into hours and days.
We must premise that the whole theory of taking time by sidereal observations is based on angular motion, the mensuration of one of the angles of motion giving a measurement of space, so that to say space, or distance, is equivalent to saying time. From noon of one day to noon of another is the whole problem to be solved by correct division. The astronomical day begins at noon, but in civil law the day is dated from midnight. So in the year the astronomical day is dated December 31, while in common reckoning the 1st of January is the initial point. This day is divided into twenty-four hours, counted in England, America, and the most of the Continental nations of Europe, by twelve and twelve. The French astronomers, however, adopted the decimal system, for ease in the computation. Thus they divided the day into ten hours, the hour into one hundred minutes, and the minute into one hundred seconds. This plan was in conformity with the French system of decimal weights and measures. Again, in Italy, the day was divided into twenty-four hours, but counting from one to twenty-four o’clock. The French system presents some features well worthy of adoption, as it gives results so much more easy in computation—a facility unattainable in the common division; yet it did not come into general use in other countries, and although some French astronomers still hold to the system, it is gradually dying out.