EEVIEWS. 
301 
tronomy will soon be removed. And we can be all tbe more hopeful of the good 
fruit to be yet borne when we reflect what the condition of amateur natural 
science was some sixteen or twenty years ago, when the microscope itself 
was as great a curiosity as some of the creatures which have since been 
revealed by it. We do not think that it is too much to expect that the 
future progress of popular astronomy shall be in the same ratio. Mr. Webb’s 
book appears to be a well-arranged one, and to contain reference to most of 
the recent advances in astronomical science. It might, we think, have been 
more amply illustrated; but we should remember that illustration is not 
always compatible with cheapness, and that the author’s object has been to 
lay before all who care for his subject a book which it is within the means 
of all to purchase. He divides his work into three parts : 1st, he deals with 
the telescope and the observer ; 2nd, he gives an account of the solar sys- 
tem ; and 3rd, he describes the so-called fixed stars. The portions of the 
treatise which appear to us to have really the highest value to the yoimg 
student are those which relate to testing the telescope, so as to detect any 
faults, and to the best mode of using the instrument in making observations. 
On these points the author is very explicit. The hints to those who are 
about to buy a telescope are so valuable that we do not hesitate to quote 
them, at least in part. ‘Hn buying a telescope,” says Mr. Webb, ^^we 
must disregard appearances. Inferior articles may be showily got up, and 
the outside must go for nothing. Nor is the character of the glass or the 
polish of the mirror any sign of excellence ; these may exist with bad figure 
(z.e. irregular curvature), or bad combination of curves, and the inevitable 
consequence, bad performance. Never mind bubbles, sand-holes, scratches 
in object-glass or speculum ; they merely obstruct a very little light. Actual 
performance is the only adequate test. The image should be neat and well 
defined with the highest power, and should come in and out of focus sharply ; 
that is, become indistinct by a very slight motion on either side of it. A 
proper test-object must be chosen. The moon is too easy ; Venus too severe, 
except for first-rate glasses ; large stars have too much glare ; Jupiter or 
Saturn are far better ; a close double star is best of all for an experienced 
eye ; but for general purposes, a moderate-sized star will suffice. Its image 
in focus with the highest power should be a very small disc, almost a point, 
accurately round, without ^ wings,’ or rays, or mistiness, or false images, 
or appendages, except one or two narrow rings of light, regularly circular, 
and concentric with the image, and in an uniformly dark field ; a slight 
displacement either way should enlarge the disc into a luminous circle. If 
this circle is irregular in outline, or much brighter or fainter towards the 
centre, or much better defined on one side of the focus than the other, the 
telescope may be serviceable, but it is not of any great excellence. The 
chances are, however, against any given night being fine enough for such a 
purpose, and a fair judgment may be made by day from the figures on a 
watch-face, or a minute white circle on a black ground placed as far oflf as 
•is convenient.” W^e have given thus much of Mr. Webb’s excellent advice, 
as a sample of the character of his book, but we have by no means included 
all his remarks, since the observations we have quoted refer especially to the 
common achromatic telescope. The author’s guidance of the observer is as 
clear as it is indispensable to the beginner. Indeed, we have no hesitation 
VOL. YII. — NO. XXYIII. 
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