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The accurate position of the foot of equatorial being known, a few minutes before the time of transit find the desired object and keep it central in the field of view, by means of the hand following movement, until the instant of transit. Now firmly clamp the telescope, as it will be exactly in the meridian, and alter the indices of the verniers until they are exactly opposite. Finally, adjust the level until the bubble is central.

If there are more adjusting screws than that in latitude, by their means the foot of the pillar should be brought level and parallel with the stone, before any adjustment is effected. An alteration in the east or west screws may be used to delicately alter the meridian position of the entire instrument. Raising the west foot will move the vernier towards the west.

To find a Celestial Object by means of the Declination and Hour Circles.

A movable hour-circle is now invariably used with equatorials, as by its use a considerable amount of calculation is avoided. The right ascension and time setting depend on the way this circle is figured. This will be easily understood if the circle is compared to a clock face and the time vernier to a hand. If the face revolved and the hand was a fixture the hours would have to be figured in an opposite direction to those usually marked on a clock face. In some forms of equatorials this plan is adopted, and therefore there are two ways of finding a celestial object.

If the circle is figured from W. to E. :

A. —Clamp the telescope to the declination given in an almanac,

allowing the error of refraction if ihe object is near the horizon.

B. —Revolve the hour-circle until it reads to the vernier with which it

turns the right ascension of the object sought.

In some forms of the Berthon equatorial the hour-circle can be connected with the clock; if this is the case, after the circle has been set to sidereal time on the lower vernier, it should be clamped to the clock axis, and no further time setting will be necessary.

C. —Turn the telescope until the lower fixed vernier reads on the lower

half of circle the sidereal time of the observation.

If the circle is figured from E. to W. :

A. —Clamp the telescope to the declination.

B. —Revolve the movable hour-circle till it reads (to the lower vernier

attached to the pier) the right ascension of the object.

C. —Turn the telescope until the movable vernier reads (on the hour-

circle) the sidereal time of the observation.

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