In the transit-room, the observer must wait till the star come round to the slit in the roof. In the dome, he turns the telescope to the object at once. The dome has also a slit like the transit-room; but, in order to accommodate the wider range of its inmate, it is made to turn round on its base, so that the slit may be always opposite the mouth of the telescope. An equatorial is a telescope so mounted that it keeps the object in view, and does not allow it to flit by as in the transit instrument. If, in travelling on a railway, you look at some near object through a telescope, you will, in order to keep the object in view, require to be constantly changing the direction of the telescope. This is precisely the case with the equatorial, only it is the motion of the earth, not the railway carriage, that requires to be compensated. The motion is produced by clock-work attached to the axis of the telescope.
We have now taken a very rapid glance at the principal instruments of an observatory; but before leaving the scene, we must bestow a little attention on the astronomer himself. What should be the most marked moral feature of his character? A distinguished Christian poet fixes on devotion:
"An undevout astronomer is mad."
But poetical sentiment does not always coincide with; stern fact. We fear that astronomers, as a class, are not marked very strongly by devotion. There is
