particular
method to those cases in which great accuracy in obtaining a direction
line and great rigidity in the material indication of that line's
position were essential or at least exceedingly desirable. Again, in
some cases presently to be noticed, he would require, not a tubing
directed to some special fixed point in the sky, but an opening
commanding some special range of view. Yet again it would be manifestly
well for him to retain, whenever possible, the power of using the shadow
method in observing the sun and moon; for this method in the case of
bodies varying their position on the celestial sphere, not merely with
respect to the cardinal points, would be of great value. Its value would
be enhanced if the shadows could be formed by objects and received on
surfaces holding a permanent position.

We begin to see some of the requirements of an astronomical building
such as we have supposed the earlier observers to plan.

First, such a building must be large, to give suitable length to the
direction lines, whether along edges of the building or along tubular
passages or tunnellings within it. Secondly, it must be massive in order
that these edges and passages might have the necessary stability and
permanence. Thirdly, it must be of a form contributing to such
stability, and as height above surrounding objects (even hills lying at
considerable distances) would be a desirable feature, it would be proper
to have the mass of masonry growing smaller from the base upwards.
Fourthly, it must have its sides carefully oriented, so that it must
have either a square or oblong base with two sides lying exactly north
and south, and the other two lying exactly east and west. Fifthly, it
must have the direction of the pole of the heavens either actually
indicated by a tunnelling of some sort pointed directly polewards, or
else inferable from a tunnelling pointing upon a suitable star close to
the true pole of the heavens.

The lower part of a pyramid would fulfil the conditions required for the
stability of such a structure, and a square or oblong form would be
suitable for the base of such a pyramid. We must not overlook the fact
that a complete pyramid would be utterly unsuitable for an astronomical
edifice. Even a pyramid built up of layers of stone and continued so far
upwards that the uppermost layer consisted of a single massive stone,
would be quite useless as an observatory. The notion which has been
entertained by s