294 
NATURE 
[ JANUARY 24, 1907 
. 5 | 
synopsis of orders arranged according to Engler’s 
syllabus, a summary of naturalised plants, and a list 
of native names. 
Side-Lights on Astronomy and Kindred Fields of 
Popular Science: Essays and Addresses. By Prof. 
Simon Newcomb. Pp. vii+350. (London and New 
York: Harper and Brothers, 1906.) Price 7s. 6d. 
net. 
In bringing up to date and publishing in book form 
this collection of essays, which have from. time to 
time appeared in various American journals, Prof. 
Newcomb has provided us with a volume which is at 
once interesting and instructive. The range of sub- 
jects is a wide one, extending from a discussion of 
the question, ‘‘ Can We Make It Rain? ”’ to the flying 
machine and the structure and extent of the universe. 
The chapter on the making and using of a telescope 
should prove interesting to anyone who uses this 
instrument, whilst ‘‘ The Fairyland of Geometry ”’ will 
provide food for thought for many hours to those 
amateur astronomers whose acquaintance with the 
science has been restricted to observation only. 
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 NATURE. 
No notice is taken of anonymous communications.] 
Radium and Geology. 
In considering the influence of radium on earth history, 
it appears to be generally assumed that the radium detected 
everywhere in the surface materials of the earth is an 
original constituent of the igneous rocks. An entirely 
different view has been lately pressing itself upon me. L 
put the view forward mainly because I think there are 
difficulties in the way of accepting the original or primary 
nature of the radium in rocks. These objections I first 
briefly state. 
The original nature of the radium cannot be maintained. 
without at the same time assuming the presence of the 
associated uranium to make good the radio-active decay. 
Now it is easy to show that if such uranium existed grave 
difficulties arise from the facts of solvent denudation. 
The ocean which receives the dissolved rock materials 
must be in an entirely different state from what is 
observed. Even assuming geological time as only a very 
few million years, the quantity of radium now in the ocean 
should be much greater than has been observed. If the 
river supply of dissolved rock materials had been sustained 
for only some 20x 10° years, the sea-salt should possess a 
richness twenty-five times as great as the ascertained 
amount. 
In stating this T make the assumptions—which I think, 
however, are not easily evaded—that radio-active substances 
are removed from the land along with other mineral 
matter, and that, along with radium brought into river 
water on the break-up of rock minerals, the postulated 
uranium is also carried to the ocean. On these assump- 
tions we can arrive at an approximate estimate of what 
should be the existing state of the ocean on any possible 
estimate of geological time. ‘ 
We do not require accurate figures. We are only really 
concerned with their order of magnitude. I take, in the 
first place, the Hon. R. J. Strutt’s estimate of the radium 
in sea-salt, stated to be approximate only. The quantity 
is 0-15X10-** grams per gram. From this there must be 
in the ocean about 8x10° grams. I assume the oceanic 
mass as 1-468 1074 grams. On Dr. Boltwood’s result for 
the value of A(year)—* for radium, to maintain this quantity 
there must in some way be brought into the ocean 
1-78X 10° grams of radium per annum. 
NO. 1943, VOL 75] 
I now turn to the approximate river supply.. We have 
Sir John Murray’s estimate of the total volume of river 
water and the dissolved matter therein, which annually 
enter the ocean. The dissolved matter amounts to 
5:1x10'° grams. If we suppose the matter in solution still 
to possess the mean radium content of the igneous rocks 
as determined by the Hon. R. J. Strutt, that is, 5x10-** 
grams per c.c. (and the application of this number can be 
justified on data at our disposal), we find that 10* grams 
of radium enter the ocean annually from the waste of the 
land. It will be seen, in the first place, that this quantity, 
unless the uranium enters along with it, is not nearly 
what is required to maintain the oceanic radium. at its 
approximate present value; but if, on the other hand, the 
associated uranium enters along with the radium, in 8x 10° 
years there would be such an accumulation of uranium in 
the ocean as to account for the existing amount of radium. 
But we have not to deal with 800,000 years. If geological 
time was but a few million years, and solvent denudation 
had progressed as here assumed, the facts as regards 
oceanic radium would be entirely different from the 
observed facts, even allowing a wide margin of error ‘in 
all the data involved. In 1ooX10° years there should be 
o-19X10-'° grams of radium per gram of sea-salt. I 
neglect the rate of decay of uranium, as this rate involves 
periods of the order of thousands of millions of years. 
Is there any way of evading this difficulty? If we 
assume the uranium to be in some way caught in the 
sediments, and so brought again into dry land, we must 
expect to find a concentration to occur in them; but the 
facts are the other way. The average radium content of 
the sediments appears to be less than half (2x10~-**) that 
of the parent igneous rocks, and is, in the case of the 
detrital sediments and on the assumption of the original 
nature of the radium, presumably what remains be- 
hind with the less soluble constituents of the parent 
rocks. Nor can we suppose the uranium retained in the 
soils, for then we must face a still more extraordinary 
concentration of radium, whereas the soils are apparently 
poor in radium. If it is supposed to be concentrated in 
the rocks beneath the soils, difficulties have to be faced 
with other heavy metals. And in this case, of course, ex- 
amination of the surface rocks tells us little as to the 
radium-content of the deeper lying rocks, save that these 
should contain much less. We are observing, in fact, 
the concentration products of about a mile and a half deep 
of parent rock removed by the wear and tear of geological 
time, and know not the depth to which these products 
extend. But such a continued accumulation on the land 
is hard to comprehend. It appears to me that the simplest 
conclusion is that there is no associated uranium generally 
distributed throughout the surface materials of the earth. 
I of course do not refer to the ore bodies, thermal springs, 
&c. Again, in certain igneous masses uranium undoubtedly 
exists occluded in the minerals, whatever history we may 
ascribe to it. 
But if there is no associated uranium, whence comes 
the radium everywhere distributed over the surface of the 
earth? It cannot be from volcanic sources. These are 
entirely too local in their influence. Nor yet can we sup- 
pose it to reach the surface, as ores in general do, by 
means of fissure veins, &c. These, again, are quite local 
in their influence. Indeed, the Hon. R. J. Strutt points to 
examples of this in the case of the uranium deposits; the 
adjacent igneous rocks were not abnormal in their radium 
content. 
By a process of exclusion, if for no other reason, we 
are, I think, justified in considering the possibility that the 
radium is picked up by the earth in its motion through 
space. The probable source would be the sun. There 
are, in point of fact, many arguments in support of this 
view besides that by exclusion. The fairly uniform dis- 
tribution over the earth’s surface at once finds explan- 
ation. The picked-up radium probably floats in the atmo- 
sphere for a long time, and ultimately is helped downwards 
to the surface by rain and snow, and other meteorological 
conditions. Once upon the surface of the land, percolating 
waters will carry it to all depths to which such waters 
penetrate. It has many thousands of years for its travels 
