222 
NATURE 
[JANUARY 7, 1897 
of objectives. The new triple photo-visual objective is 
the outcome of experiments made by Messrs. Cooke’s 
optical manager, Mr. H. Dennis Taylor, in the direction 
of improving the so-called achromatic telescope. The 
success with which he has been rewarded, has given 
astronomers an objective which is not only free from 
colour aberrations, but which can be used for celestial 
photography without the necessity of any further adjust- 
ment. 
In the present edition this new lens is fully referred 
to, and the communications of Mr. Dennis Taylor to the 
Royal Astronomical Society are reprinted in full. A 
supplementary chapter is also added, describing the 
adjustments of its component parts ; this will, no doubt, 
prove most serviceable to those who are the fortunate 
possessors of this lens. 
In the main, the general text of the book has not been 
very considerably disturbed ; modified views, and the 
insertion of up-to-date information, have of course 
required here and there changes in the text, and to some 
extent enlargement. 
Users of telescopes cannot do better than make them- 
selves thoroughly acquainted with the contents of this 
excellent and valuable source of information. It must 
be remembered that we are here enabled to make use 
of the knowledge of those well experienced in the 
making and testing of numerous objectives, and amateurs 
and others may gather many a wrinkle, the knowledge 
and use of which will make all the difference between 
the bad and good working of an objective with which 
they are making observations. Wo diccSeglh. 
Materials. By A. Humboldt 
(London: Blackie and Son, 1896.) 
THIS book is intended to meet the want of a manual 
intermediate in size between the exhaustive treatises of 
Percy, Mills, and Rowan on the one hand, and such 
brief outlines of the subject as may be found in manuals 
of metallurgy on the other. Seven chapters out of 
fifteen are devoted to fuel, one to the recovery of bye- 
products, three to furnaces and refractory materials, 
whilst the subjects of pyrometry, calorimetry, utilisation 
and testing of fuel are dismissed in one chapter each. 
The book is written in a clear and concise style, and is 
profusely illustrated with excellent diagrams. Thé sub- 
jects of coking, recovery of bye-products, and prepara- 
tion and use of gaseous fuel are treated in a very prac- 
tical manner and in great detail. The chapter on the 
important subject of pyrometry is not so satisfactory, 
as although an account is given of almost every type 
of instrument, whether obsolete or not, the impres- 
sion is given that the author has little practical know- 
ledge of many of the instruments described, as scarcely 
any criticism is offered, and the descriptions are often in 
the inventor’s own words. The result is that an engineer, 
wishing to put in a pyrometer for practical purposes, 
would receive little assistance in choosing the best type 
of instrument for any special case. An exact definition 
of the various thermometric “scales” of the several in- 
struments would also be desirable, so that the exact 
meaning of a temperature measured, say on the platinum 
resistance scale, could be clearly shown. The same his- 
toric completeness and lack of criticism applies to the 
chapter on calorimetry ; a student might get the idea 
that for practical purposes it is a matter of indifference 
whether the heat of combustion of a fuel be determined 
by Berthier’s process (fusion with litharge) or by the 
Berthelot-Mahler process. Taking the size of the book 
into consideration, very few essential points have been 
omitted. It is to be hoped, however, that in the second 
edition space may be found in Chapter x. fora description 
of an anemometer of the Fletcher type, the direct mea- 
surement of the gaseous velocity in a shaft being much 
NO. 1419, VOL. 55] 
Fuel and Refractory 
Sexton. 
preferable to the indirect methods given. The approx- 
imate analysis of flue gases is now so common in 
works, that a short account of the methods used, together * 
with an application (such as a boiler trial), would be very 
useful. The only method mentioned for carrying out 
such analyses is both cumbersome and expensive. At 
the end of the book is an admirable set of references to 
works and papers bearing on the subject. 
The Lepidoptera of the British Islands; a Descriptive 
Account of the Families, Genera and Species indigenous 
to Great Britain and Ireland, their Preparatory States, 
Flabits and Localities. By Charles G. Barrett, F.E.S. 
Volume III. HETEROCERA: Sombyces, Noctue. 
Pp. 396. 8vo. (London: L. Reeve and Co., 1896.) 
THE present instalment of Mr. Barrett’s voluminous 
work includes the following families: BOMBYCES: 
Bombycide {more correctly Lasiocampide), Endromide, 
Saturnide, Drepanulide, Notodontide. NOCTUINA: 
Cymatophoride, Trifide (Diphthera to Agrotis). 
The habits, localities and transformations of the 
various species are dealt with at considerable length, 
and practically include most of the available information 
respecting British Lepidoptera likely to be useful toa 
practical collector. Information respecting the occur- 
rence of British species abroad is likewise furnished in 
most instances, and reputed British species are also 
mentioned incidentally. 
Entomologists who do not confine their studies to 
British insects, and who are more interested in classifica- 
tion than in habits, will find Mr. Barrett’s remarks on 
the structure, pattern and classification of that extensive 
group of moths (the Mocfu@) well worth perusal. 
They form one of the most dominant groups of the 
larger moths at the present day; but they are very 
compact, and it is exceedingly difficult to find satis- 
factory characters by which they can be divided into 
families. This has been attempted by Guenée, but 
many writers since his time have abandoned the idea of 
subdividing the octue, except into genera. Mr. Barrett 
evidently recognises three main families at least ; but we 
shall be interested to see where he places some of the 
more aberrant genera usually included in the MVoectue, 
when he arrives at them in later volumes of his work. 
Flow to Study Wild Flowers. By the Rev. George 
Henslow. M.A., F-L.S., F.G.S., &c. Pp. 224 (with 
fifty-seven illustrations). (London: The Religious 
Tract Society, 1896.) 
THIS is a useful little book, and doubtless it will be 
welcome to many people who live in the country, and 
who may desire to gain a systematic acquaintance with 
the flowering plants around them. 
We could wish, however, that the author had empha- 
sised the “ Floral Formula” part of the business a trifle 
less, and had given a little more attention to floral 
diagrams instead. As regards the latter, we might 
remark that the position of the mother-axis ought always 
(if possible) to be indicated in the diagrams, otherwise 
how are his readers to tell which aspect of the 
flower is posterior and which anterior? A neglect of 
this necessary adjunct to these figures will tend to render 
such diagrams as the learner may attempt to construct 
for himself quite useless, inasmuch as his attention is not 
directed, as it ought to be, to a definite orientation of » 
the different parts of the flower. 
Some of the plants receive a somewhat desultory 
treatment ; but notwithstanding this, and in spite of some 
errors we have noticed, the book is well worth looking 
into, on account of the refreshing number of interesting 
first-hand details which it contains. 
