Itaque fix arum spha era non tantum orbe
stellarum, sed etiam circulo lactis versus not deorsum est terminata."
Our starry stratum is a disk of inconsiderable thickness, divided a
p 89
third of its length into two branches; it is supposed that we are near this
division, and nearer to the region of Sirius than to the constellation
Aquila, almost in the middle of the stratum in the line of its thickness or
minor axis.
This position of our solar system, and the form of the whole discoidal
stratum, have been inferred from sidereal scales, that is to say, from that
method of counting the stars to which I have already alluded, and which is
based upon the equidistant subdivision of the telescopic field of view. The
relative depth of the stratum in all directions is measured by the greater
or smaller number of stars appearing in each division. These divisions give
the length of the ray of vision in the same manner as we measure the depth
to which the plummet has been thrown, before it reaches the bottom, although
in the case of a starry stratum there can not, correctly speaking, be any
idea of depth, but merely of outer limits. In the direction of the longer
axis, where the stars lie behind one another, the more remote ones appear
closely crowded together, united, as it were, by a milky-white radiance or
luminous vapor, and are perspectively grouped, encircling as in a zone, the
visible vault of heaven.
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