JUNE 4, 1914] 
inquiry into the exceptional character of the latter half | 
of the year 1912. During that period the intensity of 
solar radiation appeared generally to be considerably 
below the values previously found; the decrease was 
indeed so marked that it could be detected in the 
records from the Campbell-Stokes instrument which is 
designed primarily for the registration of duration of 
sunshine. The diminution has been attributed to the 
presence in the atmosphere of an exceptional amount 
of fine dust arising from the volcanic eruption of 
KXKatmai, in Alaska, at the end of June, 1912. 
An ingenious explanation of the way in which the 
dust may stop the solar radiation without keeping 
in the earth’s radiation to anything like the same 
degree has been put forward by Humphreys, in the 
Bulletin of the Mount Weather Observatory. The 
particles of dust have a diameter almost certainly 
greater than the wave-lengths of the most intense 
solar radiation, and smaller than the wave-lengths of 
terrestrial or atmospheric radiation, sc that they would 
reflect the former but merely scatter the latter; and 
Humphrey’s calculations show that the reflection 
would be much more effective than the scattering. 
Thus the effect on the temperature at the earth’s sur- 
face is the reverse of that due to an increase in the 
absorbing power of the atmosphere, such as would be 
produced by increasing the water vapour or carbon 
dioxide in it. The theory is both novel and important ; 
it indicates a method by which purely terrestrial 
agencies may profoundly affect the mean temperature 
of the globe, which may be sufficient justification for 
this digression. 
The measurements at Warsaw bear out those found’ 
at other places; the intensity of radiation was slightly 
above the average for the earlier months of 1912, 
but from July to the end of the vear it was nearly 
20 per cent. below the average. The amount of the 
deficiency decreased in the first three months of 1913, 
and thenceforward the radiation appears to have been 
about normal. The latest values given are those for 
July, 1913. 
The only other year in the period during which the 
records show a deficiency comparable with ‘that for 
1912 was 1903 (and the last two months of 1902), after 
the eruptions of Mont Pelée, Santa Maria, and 
Colima. It will be remembered that 1903 was a year 
remarkable in this country for its excessive: rainfall 
and its disturbance of meteorological ‘statistics and 
theories of periodicity. 
The results of the whole series of measurements 
are discussed very fully for different altitudes of the 
sun, different times of day, and different conditions 
of the atmosphere, especially as regards humidity. 
The main text is in Polish, but the headings of the 
tables are given also in French, and there is a sum- 
mary in French at the end of the paper. 
; E. Gop. 
AMERICAN RESEARCH ON CLAYS.! 
CONSIDERABLE amount of interesting work 
in connection with clays and the clay industries 
has been done in recent years in Germany and in 
America, and no one has worked more enthusiastically 
than Messrs. Ashley and Bleininger. - In Germany, 
too, Drs. Rieke and Endell are doing really fine work. 
The untimely death of the writer of the first-named 
pamphlet—Mr. H. E. Ashley—was a sad loss which 
must have considerably retarded: subsequent: develop- 
ments. The clay industries the world over owe the 
Bureau of Standards, etc., in the United States a debt 
1H. E. Ashley, Technical Control of the Colloidal’ Matter of Clays; 
G. H. Brown, The Function -of Time in the Vitrification of Clays; A. V. 
Bleininger and E. T. Montgomery. Effect of Overfiring upon the Structure 
of Clays. Three ‘Vechnological Papers of the Bureau of Standards, 
(Washington, D.C., U.S.A , 1913.) 
NO. 2327, VOL. 93| 
NATURE 393 
of gratitude for having set aside such men as Messrs. 
Ashley and Bleininger to devote their whole time to 
this work, and the results must be a source of satisfac- 
tion to the authorities responsible for the innovation. 
The posthumous pamphlet by Mr. Ashley, together 
with his ‘‘The Colloidal Matter of Clay and _ its 
Measurement’’ (1g0g9), form a kind of monograph, or 
rather a brief advocating the colloidal theory as an 
explanation of the many curious properties of clays. 
Mr. Ashley was an extremist, and in consequence we 
beve here probably the best possible statement of the 
theory without those doubts and difficulties which 
perplex and hamper less enthusiastic temperaments. 
For that reason, Mr. Ashley’s brief is particularly 
valuable, even though it is certain that some of the 
applications of the colloidal theory will not be able 
to stand, in their present form, before adverse criticism. 
The colloidal theory has been mainly directed to 
explaining the plasticity of clays. The argument 
appears to run somewhat as follows :—The plasticity 
of clays is determined by the contained colloidal 
matter (and also by the degree of fineness of the 
constituent particles of the clay). The greater the 
plasticity, the greater the proportion of colloids. 
Colloids are always present in clays in unknown quan- 
tities, and the proportion of colloids in clays of differ- 
ent plasticity varies in accord with theoretical require 
ments! The amount of colloidal matter in a clay is 
assumed to be proportional to the dye-absorptive power 
of the clay, and this, in turn, is stated to be propor- 
tional to the plasticity. 
As a matter of fact, the real plasticity of a clay. is 
not. so easily measured. The potter’s thumb is the 
ultimate test, and any process of measurement must 
express by number those complex sensations which the 
| potter ‘feels’? when he estimates the plasticity of a 
clay. If measurements of the dye-absorptive power 
and of the fineness of the grain of a clay will do this, 
then the problem is solved in a most simple and in- 
teresting manner. Unfortunately, the method breaks 
down completely in practice. Consequently, we cannot 
really go further than this: the known facts favour 
the colloidal theory as the best qualitative explanation 
of plasticity yet suggested, but no one has. succeeded 
in satisfactorily demonstrating the theory quantita- 
tively. Thus we return to the view held by a writer 
in the eighteenth century, who stated that ‘the plas- 
ticity is due to the presence of a greasy medium 
between the particles of the clay.’ It is difficult to 
see how the plasticity of clays can be measured unless 
it be treated as a mechanical problem; and to the. 
present writer, Zschokke’s analysis of plasticity is far 
and away the greatest advance that has yet been 
made. 
The two other pamphlets seem to be an application 
to American clays of some ideas suggested by the 
present writer in several papers a few years ago: “‘On 
the Speed of Vitrification of Clays,” etc. Clays are 
made up of a heterogeneous mixture of particles of 
different sizes and composition; when clay. products— - 
bricks, etc.—are being fired, the more refractory par- 
ticles start dissolving in the matrix formed by those 
which melt first. In the extreme case, the whole 
would form a homogeneous vitreous mass. The firing 
is stopped before this condition is reached. The stage 
at which the process of vitrification is arrested is deter- 
mined by the nature of the required products—porce- 
lain, firebricks, ete.—and on the character of the par- 
ticular clay ‘‘body” being used. Each clay has its 
own specific character, and this explains how a fire- 
man. with no sound principles to guide him—but a 
: triumph of empiricism with one, or maybe two, types 
/ of clay—often fails ignominously when he is_trans- 
ferred: from one district to another, using a different 
type of clay. J. W. MELLor. ~ 
