608 NATURE 
[AuGuUST 15, 1912 
sometimes not only unscratched, but patinated or 
weathered. 
The patination is of the kind which is now to be 
| 
seen on flints on the present land surface, and is | 
generally, and I think rightly, supposed to have been 
caused by the slow action of various solvents present 
on that surface. 
Thus it appears probable that these stones from 
the Boulder Clay were first scratched, then broken, 
and left lying on a land surface sufficiently long to be 
patinated, and finally incorporated with the clay, 
It is also apparent that if marked striations on 
flints are a sign of intense glaciation, then those 
found at the base of the Red Crag must have been 
at some period subjected to a much greater degree of 
ice-action than was present when the Boulder Clay 
was being formed, J. Rem Moir. 
12 St. Edmund’s Road, Ipswich, July 30. 
On the Sign of the Newtonian Potential. t 
Pror. Lamp, in the second edition of his ‘‘ Hydro- 
dynamics,’’ made a change in the sign of the velocity- 
potential. Would it not be an advantage to change 
the sign of the Newtonian or gravitational potential 
also? 
If this were done, the relation connecting field and 
potential (F=—dv/ds) would be true for gravitation 
as well as for electricity, and potential would always 
be potential energy divided by mass (or charge). , Of 
course, there would be the disadvantage that the 
analytical definition yn would have to be altered to 
ee which would conflict with the corresponding 
Se Poisson’s 
expression for the electrical potential. 
equation would also have to suffer a change of sign. 
However, it might be worth while to bring the 
physical definitions into agreement even at the cost 
of these analytical inconveniences. At present it 
Sometimes happens that students are confronted with 
two irreconcilable definitions, one from the mathe- 
matical, the other from the physical, lecturer. The 
result is that they are never sure whether a plus or 
minus is to be used in any given case. 
H. Piacero. 
University College, Nottingham, August 1, 
A Point in Geological Nomenclature. 
In his review of Prof. Haug’s ‘ Traité de Géologie”’ 
(II.) in Narure of August-1,-J. W. G. asks the ques- 
tion :. ‘Should it .[the ‘ Quaternary ’?]. not be Quar- 
tary?’’ He will perhaps be, glad to be reminded, of 
the fact that, so long ago as 1887, Prof. Hermann 
Credner, of Leipzig, used the term das Quartdr (in 
linguistic consonance with das Tertiary) in the 6th 
edition of. his well-known and invaluable text-bools, 
and has retained it in the roth edition (1906), brealsing 
it up-into (a) Dilwvium (=Pleistocene) and (b) Allu- 
vium, a most convenient division. A. IRVING. 
Bishop’s Stortford, August 3. 
A Reversible Photochemical Reaction. 
In the preparation of some tungsten compounds I 
obtained a by-product which is reduced on exposure 
to sunlight, the reduction being marked by a change 
of colour and being accelerated by reducing agents. 
In the dark, in contact with the atmosphere, the 
is brought about instantaneously by oxidising agents. 
Will readers of Nature who are acquainted with 
reactions of a similar type kindly inform me of pub- 
lications on the subject? M. Rrinp1. 
Grey University College, Bloemfontein, July 8. 
NO. 2233, VOL. 89] 
| detailed 
| 
NATURE AND MAN IN AUSTRALIA} 
ROF. BALDWIN SPENCER and Mr. Gillen 
are honoured by all ethnologists as the 
authors of two notable books on the tribes 
of Central Australia which afforded us more 
information about the peoples they 
visited than had previously been given con- 
cerning any other Australian tribes, and at 
the same time gave rise to more discussion than 
has befallen any other records of savage men. 
Their last book is, from one point of view, a 
supplement to their earlier works, and from 
another it may be regarded as an independent 
record of a more general and popular character. 
“Across Australia” is not, like its forerunners, 
a monographic study of certain tribes, but, as its 
name implies, is a running commentary, so to 
speak, of a transverse section through the con- 
tinent explained by two keen and experienced 
naturalists, one of whom has spent many years in 
the heart of the continent. and had wandered 
hither and thither. The present account, therefore, 
is not the description of a single expedition, but 
combines the experiences of several journeyings, 
except so far as the most northerly third of their 
route is concerned. aha 
The broad geographical features of Central 
Australia are clearly explained; the authors evi- 
dently incline to the view that a general desicca- 
tion, which dates from the Pleistocene period, is 
still taking place. The desert and poor steppe con- 
ditions and their bionomics are well described and 
illustrated; Fig. 19, with the mesas in the back- 
ground, might very well be a photograph of a 
typical scene in New Mexico, except that the 
scattered clumps of vegetation are not sage brush. 
The characteristic plants of the several geographi- 
cal areas are described, and attention is directed 
to a change of flora or fauna during the passage 
from south to north. 
The keynote of the greater part of Australia is 
drought, and our authors give abundant evidence 
to show how all living things have to accommo- 
date themselves to variable periods of greater or 
less desiccation alternated by copious rains and 
even floods, which subside and disappear with 
great rapidity. The inexorable necessity is laid 
upon plants and animals to take the utmost advan- 
tage of the very transient humid conditions, and to 
protect themselves as best they may against 
drought. The aquatic animals especially have 
adapted themselves to these variable conditions : 
very remarkable in this respect are several species 
of frogs belonging to three genera, which fill them- 
selves, more particularly their bladder, with water 
till they become spherical, then burrow a foot or 
so in the mud, and thus tide over a year or 
eighteen months of drought. ‘‘The water is quite 
pure and fresh, and the natives take advantage of 
t ji | this supply when they cannot otherwise secure 
original colour is gradually restored. The same effect | 
” 
any. Water-beetles, snails, and other aquatic 
animals also zstivate, and their young have to 
mature quickly in order to take advantage of the 
a4 “ Across Australia." By Prof. Baldwin Spencer, C.M.G., F.R and 
Fr J. Gillen. Vol. 1. Pp xv+254+plates. Wol. 1. Pp. xviiit25s5—sts 
+plates4-maps. (London: Macmillan and Co., Ltd., 1912.) Price 21s. net. 
“Ss 
