i 
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150 
NATURE 
quite recent introduction’; for in chemical books of older 
date it was always observed, in proof of which see 
Gmelin’s “ Handbuch der Chemie” throughout. Gmelin 
indeed, in the first volume of his great work (4te Auflage, 
1843, p. 61, and English Edition, i. 61) lays down the law 
of the case as follows :—* A number placed before several 
symbols multiplies them all, as far as the next + sign or 
comma; or if it stands before a bracket, it multiplies all 
the symbols and numbers included within the brackets.” 
This rule is consistently followed all through the “ Hand- 
buch,” and, so far as I know, in most contemporary 
chemical writings ; but lately it has fallen intodisuse, and 
a numeral placed before a set of unbracketted symbols is 
supposed to multiply them all, whether separated by addi- 
tion-signs (+,.) or not. Now this last practice would 
be all very well if consistently followed out ; but unfortu- 
nately it is not, and hence confusion arises. For example, 
the formula 2SO;,H,O is used, sometimes to signify 
S,0;H., that is to say, one molecule of pyrosulphuric 
acid, while at other times it is employed to denote 
S,H,O, or 2SO,H,, ze. two molecules of sulphuric acid, 
which latter, according to earlier usage, would have been 
represented by 2(SO,, H.O). Again, in the formule of 
basic salts we find such expressions as 3Fe,0;, SO;, and 
2Fe,0;,3SO0., &c., in which the co-efficient 3 or 2 is 
understood to multiply only the Fe,O,, without affecting 
the SO,; these formule being in fact identical with 
SO,, 3Fe,C3; and 3SO,, 2Fe,0, respectively. Now it is 
easy to see that this varying practice in the use or omis- 
sion of brackets must lead to confusion, and it is much to 
be desired that the rule which formerly prevailed should 
be restored to use. 
In conclusion, I hope it will be understood that the 
preceding criticisms are offered solely with the view of 
promoting uniformity in our nomenclature and notation, 
and by no means in disparagement of the volume under 
review, which is in every way a useful and valuable 
. addition to English chemical literature. H. Watts 
OUR BOOK SHELF 
Inorganic Chemistry, Theoretical and Practical. An 
Elementary Text-Book. By William Jago, F.C.S., &c. 
(London; Longmans, Green, and Co., 1881.) 
Practical Chemistry. Adapted to the First Stage of the 
Revised Syllabus of the Science and Art Department. 
By J. Howard, F.C.S., &c. (London and Glasgow: 
William Collins, Sons, and Co., Limited, 1881.) 
THE first-named of these books is a really good text-book 
for laboratory use; the experiments are clearly described ; 
most useful “Jaboratory hints” are given ; conclusions 
are carefully drawn from the experimental data obtained. 
The methods for proving the definition of boiling point, 
for illustrating the manufacture of sulphuric acid, and for 
confirming quantitatively the equation KCIO, =O, + KCl, 
are especially to be praised. The student who works 
through this book will have laid a good foundation on 
which he may afterwards build; only let him skip those 
parts which deal with “chemical philosophy.” Why 
should he begin his chemical career by learning that 
“combining weight” is synonymous with “ atomic 
weight” (p. 31)? Why should he trouble himself with 
committing to memory the “atomicity’’ of the most im- 
portant elements as given on p. 27 of this book? Why 
should he draw from the statement of Avogadro’s law 
the erroneous conclusion that “the molecules of all gases 
are of the same size”? Why should he deceive him- 
mn _— 
[Dec. 15, 1881 
hy ae 
self by fancying that the formula Lae (p. 143) 
iy 
4 
gives him accurate and well-grounded information regard- 
ing the molecule of nitrous oxide? No good reason can 
be given for doing any of these things, therefore let the 
student use this book as a laboratory guide only, and he 
will doubtless find it a trustworthy guide. ’ 
Could Mr. Howard's chemical philosophy be separated 
from his directions for conducting experiments, his book 
might also be recommended to the student of practical 
chemistry. . 
Although this book deals with laboratory experiments, 
one is much tempted to think that the author does 
not really regard chemistry as an experimental science. 
He deals with the general principles of chemical science 
too much from a literary point of view. An instance of 
this method is found in the preface, where we are told that 
“in former editions . . . the notation of Dr. Frankland 
was alone used... . In the present edition, however, it 
has been thought advisable to give, in addition, the nota- 
tion and formula used by Professors Roscoe, William- 
son, Thorpe, and others.’’ This sentence is decidedly 
humorous; it connects so closely phenomena which 
appear to the student of chemistry to have but little in 
common. 
Authoritative statements from the text-books exert a 
great influence on the author of this book; witness a 
sentence on p. 62: “A molecule must have all its bonds 
engaged, that is, it cannot combine with any substance 
without altering the arrangement of the atoms. Hence, 
there must always be an even number of domds in the 
molecule of any element or in any compound.’ Nitric 
oxide is of course formulated as N,O,; no hint is given 
that the molecular formula of this gas is NO. 
The first few pages contain many excellent examples 
of the misuse of that much misused word “ force.” 
LETTERS TO THE EDITOR 
[Zhe Lditor does not hold himself responsible for opinions expressed 
by his correspondents. Neither can he undertake to return, 
or to correspond with the writers of, rejected manuscripts. 
No notice is taken of anonymous communications. 
[The Editor urgently requests correspondents to keep their letters 
as short as possible. The pressure on his space ts so great 
that it ts impossible otherwise to ensure the appearance even 
of communications containing interesting and ncvel facts.] 
Primitive Traditions as to the Pleiades 
Mr. Justice HaLisurTon’s letter of December 1 (vol. xxv. 
p. 100) will have been read by many as calling attention to a 
curious subject. As it refers especially to me, and indeed arises 
out of my remark on the story of the ‘* Lost Pleiad” in 
Daw:on’s ‘‘ Australian Aborigines” (NATURE, vol. xxiv. p. 
530), I now write a few lines in reply. But it will not be 
pos-ible to di-cuss properly Mr. Haiiburton’s ideas as to the 
Pleiades till he publishes them io full, with the evidence on 
which he grounds them. It must not be supposed that the sub- 
ject has been unnoticed till now by anthropologists. That the 
Pleiades are an important constellation, by which seasons and 
years are rezulated among tribes iu distant parts of the world, 
that they are sometimes worshipped, and often festivals are held 
in connection with their rising, that their peculiar grouping has 
suggested such names as the *‘ dancers,” or ** hen and chickens,” 
and that numbers of myths have been made about them—all 
this has long been on record, though in a scattered way, and at 
any rate itis well known to students. Mr. Haliburton’s letter 
shows that he has new information to add to the previous stock, 
and furthermore that he has formed a theory that the Pleiad 
beliefs go back to a marvellously remote period in the history 
of man, when these stars were, as he says, the ‘‘ central sua” of 
the religions, calendars, myths, traditions, and symbolism of early 
ages. If the astronomical evidence is to support so vast a structure 
as this, it need hardly be said that it must go far beyond what Mr. 
/ 
