Nov. 17, 1881] 
atoms are supposed to form closed chains. Objections 
have sometimes been raised against this division as 
somewhat arbitrary ; but we cannot help thinking that it 
is justified by the peculiar kind of isomerism, depending 
on the relative position or “orientation” of the substi- 
tuted groups or radicals which exists amongst benzene 
derivatives. 
The formation, constitution, and general properties of 
the Paraffins are next explained, together with those of 
the several groups of bodies, Alcohols, Acids, Amines, 
&c., derived from them by substitution, and the remainder 
of the volume is devoted to the special description of 
these several compounds, which are arranged according 
to the number of carbon-atoms contained in them, begin- 
ning with the lowest or Methyl-group, the fundamental 
hydrocarbon or paraffin of each group being first de- 
scribed, and then in succession the Alcohols, Ethers, 
Nitrogen-bases, Phosphorus-bases, Organo-metallic com- 
pounds, Aldehydes, Acids, Ketones, Sulphur-compounds, 
&c., derived from it. 
All these compounds are clearly and ably discussed, 
especial attention being given to those which are of in- 
dustrial importance, ¢.g. common Alcohol, Acetic Acid, 
and the Higher Acids of the Fatty series, which enter 
into the composition of soap. Several industrial processes 
are described in considerable detail, and amply illustrated 
by figures, e.g. the separation of the Paraffin-oils by frac- 
tional distillation, the manufacture and rectification of 
Alcohol, the testing of the strength of Spirits and of Wine 
and Beer, the preparation of Vinegar, and the manufacture 
of Soap. And here perhaps it may not be out of place to 
point out the great practical importance of Organic Che- 
mistry, which, strange to say, has been called in question 
by some writers in the periodical press, who have spoken 
of it as consisting, in great part, of elaborate trifling about 
compounds of little practical importance, but rejoicing in 
names of fearful length, and formule of excruciating com- 
plexity--and in fact treating this branch of chemical 
science as altogether of second-rate importance in com- 
parison with Mineral Chemistry. Now the importance 
of this last-mentioned branch of chemistry, which in- 
cludes the description of the Metals and their Compounds, 
is of course beyond all question ; but it is perhaps not 
too much to say that at least an equal value in a practical 
point of view may be ascribed to that department of the 
science which is concerned with the materials of our food 
and clothing, and with the constitution of the compounds 
which make up the bodies of plants and animals. To 
remove any doubt that may yet exist as to the practical 
importance of Organic Chemistry, we can imagine nothing 
more effectual than a perusal of the volume under con- 
sideration, the appearance of which will doubtless be 
hailed with pleasure by all who are interested in the 
subjects of which it treats. H. Watts 
OUR BOOK SHELF 
Acoustics, Light, and Heat. By Thomas W. Piper. 
(London: George Philip and Son, 1881.) 
THISs little work is not without its merits, the descriptions 
of the simpler phenomena and laws of these branches of 
physics being for the most part clear, accurate, and 
couched in easy language. The arrangement adopted in 
the chapters of the book is a departure, and we think not 
NATURE 51 
a very wise one, from the usual order of subjects in ele- 
mentary text-books of physics. After a preliminary 
chapter on the atmosphere, its elasticity and its weight, 
the author plunges into vibratory motion, and under this 
head treats of acoustics. Chapter III. is on rectilinear 
motion, under which heading we have the following sub- 
jects :—The reflection of sound, the linear propagation 
of light, reflection of light and its applications, convection, 
radiation, and conduction of heat, laws of curved mirrors, 
laws of refraction, lenses, magic lantern, refraction of 
sound, spherical aberration of lenses, and, lastly, proper- 
ties of matter. We have quoted these in the order in 
which they occur, and cannot help thinking that, however 
clearly the individual subjects are treated of, this hetero- 
geneous lumping together of them must hamper the 
comprehension of beginners. Chapter IV. deals with 
the conservation of matter, including expansion by heat ; 
Chapter V. is on thermometers. Chapter VI., on the 
conservation of energy, is another example of the author’s 
peculiar method. It begins with the correlation of forces, 
deals with the prismatic spectrum, diathermancy, acoustic 
resonance, the laws of vibrations of strings, and specific 
heat. The book concludes with a chapter on sensation, 
optical and acoustical. Except for these aberrations of 
arrangement, and for one or two slips, the book would be 
a satisfactory one for beginners in natural philosophy. 
LETTERS TO THE EDITOR 
[The Editor does not hold himself responsible for opinions expressed 
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No notice is taken of anonymous communications. 
[The Editor urgently requests correspondents to keep their letters 
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that it ts impossible otherwise to ensure the appearance even 
of communications containing interesting and novel facts. | 
The Parasitic Habits of Molothrus 
IN the ‘‘ Origin of Species” I adopted the view maintained 
by some writers, that the cuckoo lays her eggs in other birds’ 
nests, owing to her habit of laying them at intervals of two or 
three days ; for it could hardly fail to be disadvantageous to her, 
more especially as she has to migrate at a very early period, to 
have young birds of different ages and eggs all together in 
the same nest. Nevertheless this occurs with the non-parasitic 
North American cuckoo. If it had not been for this latter case, 
it might have been argued that the habit of the common cuckoo 
to lay her eggs at much longer intervals of time than do most 
other birds, was an adaptation to give her time to cearch for 
foster-parents. The Rhea or South American ostrich is believed 
likewise to lay her eggs at intervals of two or three days, and 
several hens deposit their eggs in the same nest on which the 
male sits ; so that one hen may almost be said to be parasitic on 
another hen. These facts formerly, made me very curicus to 
learn how the several species of Molothrus, which are parasitic 
on other birds in very varying degrees, laid their eggs; and I 
have just received a letter from Mr. W. Nation, dated Lima, 
September 22, 1881, giving me information on this head. He 
says that he has there kept in confinement for a long time 
Molothrus perpurascens, and has likewise observed its habits in a 
state of nature. It is a resident species of Western Peru, and 
lays its eggs exclusively in the nests of a sparrow (Zonotrichia), 
starling (Sturnella bellicosa), and a pipit (2nthus chiz). He 
then proceeds: ‘‘ The eggs of the sparrow are very much like 
those of the Molothrus in size and colour. The eggs 
of the starling are larger and somewhat different in colour ; 
while the eggs of the pipit are very different both in size 
and colour, Generally one egg: of the Molothrus is found in 
a nest, but I have found as many as six. The young Moloth- 
rus does not always eject its foster-brothers; for I have seen 
a young one nearly fully feathered in a nest with two young 
