REVIEWS. 
57 
It would be impossible in tbe space of this short review to indicate more 
than a small fraction of the total number of imperfections which we have 
noticed in looking- through the volume. On page 16 we find it stated that the 
mirrors of reflecting telescopes are usually made of speculum metal, though of 
late years excellent mirrors have been made of silvered glass, whereas there 
has been scarcely a mirror made of speculum metal for a quarter of a 
century, and over ninety-nine per cent of the reflecting telescopes in use have 
silver-on-glass mirrors. Pages 79 to 88 are devoted to the transit instru- 
ment and its corrections, though the very lengthy account would be quite 
insufficient to enable any one to take and reduce a transit, and it contains an 
extraordinary definition of the error of collimation, — the axis of collimation 
being- defined as the line from the centre of the object-glass to the inter- 
section of the central cross wires ! Towards the end we have a selection 
of star catalogues given as the most generally useful : these are the British 
Association Catalogue ! Argelander ! ! and Lalande ! ! ! Not a single cata- 
logue from which a decent star-place could be derived, and all based on 
observations made near the beginning of the century ! On page 283 
we are favoured with a peculiar description of the lunar mountains, and 
the so-called lunar craters are spoken of as the nearly extinct craters of 
once active volcanoes, and as being several hundred in number ! The illus- 
tration given as that of a typical lunar crater is curiously unlike anything 
on the face of the Moon. The picture of the Moon would not be so bad 
did not the shadows give rise to the question whether there were not two 
suns shining on it. The author also speaks of the absence of any penumbral 
fringe to the border between light and darkness on the Moon as proving the 
absence of any sensible atmosphere, whereas the actual existence of a broad 
penumbral fringe is well known to every lunar observer ; and it is also 
known that no possible atmosphere on the Moon would produce such a 
broad fringe of this nature. On pages 115-123 we find a long account of 
the parallel-wire position-micrometer and its use, but no account of how 
the position-angles are to be determined, or even what they are. Later 
(page 332) we are told what a position-angle is, but not in what direction 
it is measured, so that the earlier information is useless. On page 326 we 
are told that 1 it is at present, at all events, quite out of the question to 
suppose that a quantity so minute as the Sun’s diameter could be detected 
by our instruments a startling statement, followed as it is by the addition 
that even were it ten times as great, it would be barely appreciable. It is to 
be trusted that the context will show the student that this means ( if the 
Sun’s diameter seemed two hundred thousand times smaller than it does 
to us.’ 
The whole character of the book may be summed up as a little badly 
selected astronomy very diffusively treated with the aid of elementary 
geometry — a work neither sufficiently trustworthy nor sufficiently complete 
for the purpose it aims at. Its principal virtue is the clear and lucid 
manner in which it is written, the distinctness with which the various 
mathematical principles are enumerated, and the capital index with which 
it is furnished. As a text-book of Astronomy, however, it is certainly 
not to be recommended to any one wishing to obtain a full and trustworthy 
account of Modern Astronomy. 
