under a spider's line stretched in the field of view of the fixed microscope, and this gives him the required altitude of the star. The measuring apparatus is so perfect, that the position can be read off to the fraction of a second. The transit-circle is one of the most perfect productions of art, both in regard to its optical and measuring powers. It was executed at Munich, the metropolis of art. Most of the finest instruments of European and American observatories have been sent forth from the workshops of this city. It is, however, satisfactory to note, that the tide seems to be once more turning in favour of our own country, for the recently-executed transit-circle at Greenwich is entirely of home manufacture, and its performance is quite unmatched.
When reference is made to the delicate measurements of the astronomer, it is satisfactory to have a clear conception of what the minute divisions mean. Now, what is meant when it is said, that such an instrument reads to the fraction of a second? How far distant from one another must the slender lines be which include a second of space? Some notion of this extreme closeness may be formed, when we state, that about six thousand lines would be crowded into the space of an inch on the limb of a circle six feet in diameter, and yet the astronomer has to deal with even minute fractions of the intervals between these lines. The distances of the fixed stars depend on the measurement of quantities so minute. It was not till
