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[138] from this is obtained directly the declination, or distance from the celestial equator. The time of a star's transit is signalled, by means of an electric transmitter in the operator's hand, to a chronograph which records the beats of the astronomical clock in the basement. This chronograph was invented by Professor Bond and was very quickly adopted in other observatories. The time observed gives the star's right ascension which corresponds to terrestrial longitude, as declination does to terrestrial latitude.

The meridian circle is the most accurate means of obtaining the exact position of stars. These positions are recorded in the star catalogue. It is also the most accurate means of obtaining true time. Until very recently Boston obtained its true noon from this observatory. Now, however, the time is telegraphed daily from the observatory at Washington, and the Harvard time service has been discontinued.

A beautiful little brass instrument in the same room, not more than three feet high, is a transit instrument made in Russia. It can be used, like the meridian circle, for obtaining the time of meridian transit of stars, but not for declinations, as there is no circle attached to it.

The astronomical clock is in the basement, and is interesting to look at with its three dials, one for each of the three hands. It is regulated to sidereal time; that is, it makes its round of twenty-four hours between two successive passages of the same star over the meridian, thus gaining about four minutes a day over solar time. This clock is, perhaps, the most important instrument in the observatory, for it is essential to the proper use of Zzz the other instruments. A fine new clock Zzz

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