_ OcrTosBER 16, 1913] 
great preponderance of basic types. In the neigh- 
-bourhood of Leipa occur numerous volcanic plugs 
and necks, composed of various alkaline basalts 
and trachydolerites, with tuffs of corresponding 
nature. In addition, dykes with a N.E.-S.W. 
direction are met with throughout the whole 
district. These have a wider petrographical 
range, and are discussed at length by the author. 
The most basic rocks of this series contain 50 per 
cent. of olivine, with melilite, biotite, haiiyne, 
nepheline, &c, To this type the author gives the 
name polsenite, but it does not seem to differ 
essentially from alnéite. From this extreme the 
rocks range through melilite- and nepheline- 
basalts, haityne-basalts, and various trachy- 
dolerites to phonolites, the most acid term being 
a trachytoid phonolite very rich in sanidine. The 
silica percentage ranges from less than 30 to 58. 
The whole assemblage of dyke-rocks is regarded as 
a single series, derived from a common magma 
by differentiation along definite lines. This con- 
clusion is enforced by chemical analyses, fourteen 
in number, which yield smooth curves when plotted 
_onadiagram. The author connects the differenti- 
ation with progressive crystallisation in the 
original magma, of trachydoleritic composition; 
and for a series of rock-types so related he pro- 
poses the term pexitropic. 
Elements of Water Bacteriology with Special 
Reference to Sanitary Water Analysis. By 
S. C. Prescott and C, E. A. Winslow. Pp. 
xiv+318. Third edition. (New York: John 
Wiley and Sons, Inc.; London: Chapman and 
Hall, Ltd., 1913.) Price 7s. 6d. net. 
ATTENTION has been directed in these columns to 
the previous editions of this work; to the first on 
July 7, 1904 (vol. Ixx., p. 221), and to the second 
on November 5, 1908 (vol. Ixxix., p. 6). In view 
of the important progress made during the fast 
five years in sanitary bacteriology, the authors 
have thoroughly revised their work. Newer ideas 
on the effect of temperature upon the viability 
of bacteria in water are included; the recent 
recommendations of the committee on standard 
methods are discussed; the description of the 
isolation of specific pathogenes from water has 
been largely rewritten and much extended; and a 
new chapter on the application of bacteriology to 
the sanitary study of shellfish has been introduced. 
Metallography. By Dr. Cecil H. Desch. 
xi+431. Second edition. (London: 
mans, Green and Co., 1913.) Price gs. 
_ Tue first edition of this book was reviewed in the 
issue of Nature for January 5, 191i (vol. Ixxxv., 
p- 301). In the present work the general plan 
and arrangement of the first edition remain un- 
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most important results of recent investigations 
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_ been made in the treatment of the physical pro- 
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and steel, 
NO. 2294, VOL. 92] ‘ 
Pp. 
Long- 
NATURE 
197 
LETTERS TO THE EDITOR. 
| [The Editor 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 intended for 
this or any other part of Naturr. No notice is 
taken of anonymous communications.] 
The Piltdown Skull and Brain Gast. 
Tue discovery of the fragments of the Piltdown 
| skull has given rise to a problem of a new kind. 
| In all former discoveries of the remains of ancient 
man the part of the skull actually found was intact, 
or, if broken, a sufficient number of pieces were 
| recovered to render reconstruction an easy task. In 
| the case of the Piltdown skull, although the greater 
part of the bony walls of the cranial cavity were 
| 
| found, a large area of the forehead and along the 
middle line of the roof of the skull are still missing. 
| The problem that has to be solved is: How much is 
| missing? The solution of the problem, as Dr. Smith 
| Woodward realised when he commenced his work of 
15 9 c 9 2. 
7 
vi 
i 
| 
i 
- 2 
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s-007 7 
IF 
' 
1 
‘ 
‘(| 
my 
Fic. 1.—Occipital aspect of the brain-cast of the Piltdown skull as recon- 
structed by Dr. Smith Woodward. The parts missing in the skull are 
represented by vertical shading. 
restoration, lies in the hinder or occipital wall of 
the skull. The fragment which Dr. Smith Wood- 
ward himself discovered gives a definite index to the 
width of the right half of the occipital bone, and 
also to the width of the hinder or occipital part of the 
head. 
| It is clear, then, that the first step in the recon- 
| struction of the Piltdown skull must be an accurate 
| adjustment of the parts which enter into the forma- 
| tion of the occipital wall. If a mistake is made in 
| this initial step, then the error may become propor- 
| tionately greater as one proceeds towards the region 
of the forehead. In my opinion, Dr. Smith Wood- 
ward has made a grave mistake in his restoration of 
| the occipital region, and therefore the brain cast 
which he obtained from his reconstruction—the basis 
of Prof. Elliot Smith’s preliminary note to the Geo- 
logical Society—does not give an accurate representa- 
tion of either the size or general form of the brain of 
Piltdown Man. , 
The nature of the problem and the manner of its 
solution will be made clear-by the three accompanying 
figures. Fig. 1 represents the occipital aspect of the 
