JANUARY 31, 1907 | 
NATURE 319 
science they profess to write about, or imagine that 
a description of the bones and a few other anatomical 
facts constitutes physiology so far as the general 
public are concerned. There are, of course, some 
books which are notable exceptions to this rule, but 
we never remember to have seen one before which 
so admirably fits the purpose for which it is written 
as the little treatise before us, which the authors have 
labelled *‘ The Human Mechanism.” 
A little anatomy has, of course, to be introduced, 
but this is kept in the background; what comes to the 
front is the study of function; this is well up to date, 
and the first half of the book is a clear and succinct 
account of modern physiological knowledge. It 
avoids unnecessary details, but omits nothing essen- 
tial. It is so lucidly written that the wayfaring man 
will have to be a terrible fool if he does not under- 
stand it. 
From such a sure bed rock, the authors pass on in 
the second part of the book to the application of 
physiological laws, and treat of personal, domestic, 
and public hygiene in turn. We can award to this 
part no higher praise than to say that it is as excellent 
as the preliminary physiological portion. It teems 
with sound practical common sense; it points out con- 
vincingly, avoiding too great technicality, the scientific 
reason for their faith. If the people at large and 
their rulers could be induced to act on its precepts, 
preventive medicine would indeed make a yreat stride 
in the battle man is always waging against disease ' 
and the consequences of his misdeeds. 
Avithmélique graphique. Introduction a@ l’Etude des 
Fonctions arithmétiques. By G. Arnoux. Pp. xx+ 
226. (Paris: Gauthier-Villars, 1906.) Price 7.50 
francs. 
AssIstED by M. Laisant, the author has put into an 
interesting and occasionally novel form the elementary 
theory of congruences, indices, and residues of 
powers. He has also given various examples of the 
use of Galois’s imaginary units, and of the solution 
of cubic congruences by means of Cardan’s formula. 
There is nothing essentially new in the book, but it 
is entertaining as the work of an amateur who has 
looked at the subject in an independent way, and has 
occasionally put the facts into an unusually vivid 
form, for instance when he gives a chess-board 
diagram showing the solutions of x*+ y7{||2 (mod 5), 
and so on. 
Familiar Trees. By Prof. G. S. Boulger. 
160. (London: Cassell and Company, Lid., 
Price 6s. 
Pp. vi+ 
n.d.) 
As the author informs us in his preface, the books is 
an endeavour to describe the beauties of our familiar 
trees. He further points out that ‘‘ Their many 
associations have interests that appeal to the historian 
and the moralist, to the student of literature and of 
follx-lore, but little less than to those interested. in 
botany.’’ . . ..‘‘ The time has gone by when we could 
be content to stand agape at the wonders and 
beauties of the world of Nature; we require now some 
attempt, at least, at an analysis of the origin, pur- 
pose and significance of the objects of our admira- 
tion.’”’ Mr. Boulger has certainly given a_ fairly 
interesting account of a few of the commoner trees 
and shrubs. In his introduction he defines trees as 
perennial plants with a principal stem of some con- 
siderable diameter, rising from the ground and 
forming wood. Their woodiness distinguishes them 
from all herbs, and their one principal stem from 
shrubs. In spite of this, however, he includes in his 
book of familiar trees shrubs and even climbers, while 
such familiar trees as the oal, beech, and the lime 
NO. 1944, VOL. 75] 
are omitted and the Scots pine dismissed with a 
passing reference. 
The author has, however, brought together a con- 
siderable amount of interesting material concerning 
| the species with which he deals, and the value of the 
book is greatly enhanced by the many beautiful 
coloured plates and photographs. The appearance of 
the cross-section of the wood of the various species is 
well illustrated by selections from Mr. J. A. Weale’s 
unique collection, and these, like the other plates and 
figures, do great credit to the artists by whom they 
were produced. 
LETTERS TO THE EDITOR. 
{The Editor does not hold himself responsible for optnions 
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 NATURE. 
No notice is taken of anonymous communications.] 
Radium and Geology. 
Arter reading Arrhenius’s vivid account’ of the bom- 
bardment of the earth by electrically charged solar dust, 
one is prepared to appreciate Prof. Joly’s hypothesis as set 
forth in his letter in Nature of January 24. On the other 
hand, Mr. Strutt’s- analysis of granite affords strong sup- 
port to the view that the radium. it contains is of terrestrial 
origin. The concentration of this constituent in the biotite 
might conceivably be due to the absorption of percolating 
water containing radium in solution, but not in the zircon, 
a mineral w hich is as impermeable as quartz. A mineral 
analysis of Cornish granite from Penrhyn, made by Miss 
Davies in our geological laboratory, Ae the following 
results :—orthoclase, 24:62 per cent.; albite, 13-42 per 
cent. ; quartz, 40-23 per cent. ; Meecevite. 10-05 per cent. ; 
biotite, 11-46 per cent.; magnetite and zircon, 0-16 per 
cent. The heavy portion of the Cornish granite analysed 
by Mr. Strutt, which was insoluble in hydrochloric acid, 
consisted of silica hydrate and zircon, and if the latter 
mineral was present to the extent of 0-16 per cent. only, it 
must have contained, judging from the analysis, 
0-637xX10-'* gram of radium per gram, or a little less 
than was found in crystals of zircon from North Carolina. 
In the consolidation of granite, the zircon crystallises out 
first, then the biotite, next the muscovite, afterwards the 
albite, and, finally, the orthoclase and quartz; but the 
concentration of radium diminishes in a similar order, a 
correspondence that can hardly be the effect of chance. 
In the formation of granite, water has undoubtedly 
played a large part, and may have had a good deal to do 
with its differentiation from the parent magma. Water 
forms one of the constituents of bictite, sometimes to the 
extent of 10 per cent. Thus it is possible that the rich- 
ness of granite in radium is due to the removal of this 
constituent in solution from the general mass of a magma 
and its concentration in certain portions which were con- 
verted by hydration into granite. 
But if this be true of granite, 
well of basalt and other basic rocks in which also water 
plays its part, though to a less extent? All the igneous 
rocks to which we have access are very superficial parts 
of the earth’s crust, and it is unsafe to reason from them 
to the deeper underlying regions. There may be other 
causes, apart from solution, by which electrically charged 
atoms like those of disintegrating radium have found their 
way up from below to enrich the outermost layers of our 
planet. In any case, the assumption that radium is 
uniformly distributed through a crust forty-seven miles in 
thickness seems to require support from independent 
evidence, and until that is forthcoming it is equally open 
to us to assume a thick crust, 800 miles, consisting of 
silicates. with radium distributed through it according to 
some unknown law, but with a rapid increase towards the 
zone affected by highly heated waters. 
January 26. W. J. Sottas. 
1 Arrhenius, ‘‘I ehrbuch der kosmischen Physik, 1¢03," p. 149. (Leipzig.) 
may it not be true as 
