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122 NATURE 
and animals, was given by Mr. Ernest Hart at one of 
the many meetings which have been held on the sub- 
ject, when he mentioned that wax. manufacture had 
been, during the last twenty years, successively driven 
further and further from the centre of London. Ten 
years ago it was possible to bleach wax in the sunlight at 
Shepherd’s Bush, but the factory was now removed to 
near Richmond, as it was found that the bleaching power 
of the sun for the greater part of the year was almost 
nullified by the pall of smoke which hangs over the 
metropolis. We shall not speak to-day of the various 
appliances of which we have as yet had but a hasty view, 
but it is only fair to say that there are shown at the 
Exhibition a number of grates, some of which, such as 
the new “ Everitt’’ grate shown by Messrs. Barnard, 
Bishop, and Barnard; Mr. Crane’s grate, shown by 
Deane and Co.; and in some respects the “ Excelsior ” 
grate of Mr. Archibald Smith, mark distinct advance. 
The possibility of consuming the smoke of bituminous 
coal in ordinary grates by forcing the draught of air and 
smoke downward through the fire before it is allowed to 
escape has been shown, as hasalso the facility with which 
hard anthracite smokeless coal will burn in open grates 
without any sort of blower or other such contrivance. 
In addition to the-e there is an extremely interesting 
series of exhibits of mechanical stokers, fire-bars for fur- 
naces, a new gas-kiln which will be shown in operation, 
as well as Dr. Siemens’ gas-regenerator. Some extremely 
good household stoves and fire-places are sent from 
Germany and Canada. 
DOUBLE-STARS 
Observations of Double-Stars made at the United States 
Naval Observatory. By Asaph Hall, Professor of 
Mathematics, United States Navy, and Rear-Admiral 
Rodgers, U.S.N., Superintendent. (Washington : 
Government Printing Office, 1881.) 
E welcome another addition to our knowledge of 
the positions and distances of double stars. Prof, 
Asaph Hall has published a volume containing 1614 obser- 
vations of such stars made by him chiefly with the 26-inch 
refractor at the Naval Observatory at Washington. The 
objects of the observations are two. Firstly, the detection 
of constant errors of observations by the measurements 
of double-stars from a selected list, and comparing such 
measures with those of other observers made as nearly as 
possible simultaneously; and, secondly, the measurements 
of double-stars generally. 
The list of stars adopted is that prepared by Otto Struve, 
with a few additions of stars of greater distance. There 
are 30 stars in all, and 296 complete sets of measures of 
these have been made, each set consisting of four measures 
of position and two double measures of distance, except 
in cases where the stars exceed 3” in distance, when four 
were taken. The measures appear to be made with 
care, and the discrepancies are not greater than may be 
expected from night to night. 
In connection with this subject Prof. Hall has applied 
a geometrical test to such observations by means of 
measures of the multiple stars = 2703 and = 311 and the 
stars in the trapezium of Orion, He says :— 
“In the case of three stars A, B, C, if we take the | 
origin of co-ordinates at A, and observe the angles of 
position and the distances of B and C only, then these 
quantities are independent, and we may put their differen- 
tials equal to zero. But if we observe also the angle of 
position and the distance between B and C we have ob- 
tained more quantities than the geometrical conditions 
require, and must adjust the parts of the triangle by the 
method of least squares.” 
In the case of the triangles and the quadrilateral there 
appear to be no important systematic errors. 
Prof. Hall gives a detailed account of the use of “rough 
circles’’ for setting the instrument on a star. These 
circles are the edges of the ordinary setting circles divided 
by lines of black paint on a white ground so as to be read 
without trouble, a method already adopted in some obser- 
vatories in this country. He also describes the difficulties 
he has had with the driving clock, difficulties which are 
too often experienced with driving clocks of all kinds, 
and often arising from insufficiency of power and strength 
of parts to stand varying strains, and often dust and 
damp, which ordinary clocks do not generally experience. 
The dome, which is 42 feet in diameter, now turns with 
more difficulty, and if our experience is worth anything, 
such a difficulty once commenced will keep on fast in- 
creasing, and will very materially militate against the 
continued use of the instrument beneath it. The flexure 
of the telescope, which is 31 feet in length, and of the 
mounting, is small, and the working of the instrument 
very satisfactory. 
A filar micrometer has been used for all the observa- 
tions, and great care has been taken to test its accuracy, 
which is all that can be desired; but we note that the 
wires are illuminated by a lamp held by an assistant, a 
method somewhat primitive, as Prof. Hall says, and a 
waste of energy which might, we should have thought, 
have been useful elsewhere. 
In all the ordinary observations four measures of posi- 
tion and two double measures of distances have been 
taken, and in all cases the head of the observer was kept 
in an upright or natural position. Owing to this we shall 
expect to find, on comparison of the list of test stars with 
others, a considerable error depending on the position of 
the stars with the horizon. No doubt practice hasa great 
deal to do with it, but we have generally understood that 
the observations were more accurate and differed less 
inter se when made with line joining the eyes parallel to 
that joining the stars under observation. 
Prof. Hall has included a good many very close stars, 
and it is to them that the large telescope can be most 
profitably turned, leaving the wider ones for the small 
instruments, with which they are well able to deal. 
OUR BOOK SHELF 
Zoological Atlas (including Comparative Anatomy), with 
Practical Directions and Explanatory Text for the 
Use of Students. Invertebrata. By D. M‘Alpine. 249 
Coloured Figures and Diagrams. (Edinburgh and 
London: W. and A. K. Johnston, 1881.) 
Tuis Atlas is prefaced by the following remarks :—“ In 
treating of the Invertebrata I have thought it advisable 
to depart slightly from the plan followed with the Verte- 
brata. There are five great divisions of Vertebrates 
recognised by naturalists, and a type or so of each was 
found to answer the purpose in view ; but among Inverte- 
brates the range of structure is immensely greater, and 
