DECEMBER 25, 1913] 
“It may be that if each day, or, better still, twice 
each day, a more detailed map of the wind provinces 
were drawn, and as much information of the upper 
currents obtained as possible, it would assist to 
elucidate many obscure questions relating to rainfall. 
Of late years the steady improvement of the charts 
given in the Weekly Weather Reports of the Meteoro- 
logical Office has been very noticeable. If the charts 
were twice the size and the evening observations dealt 
with as fully as the morning, a great step in 
advance would be made. R. M. Deetzy. 
_Abbeyfield, Salisbury Avenue, Harpenden, 
November ‘13. 
Amehbocytes in Calcareous Sponges. 
Wuen Prof. Dendy, in Narure of December 4, 
writes that ‘‘the Amcebz referred to by Mr. Orton 
. . . possibly . were . . - metamorphosed collared 
cells,’’ he must have failed to notice the dimensions 
given by Mr. Orton, 
A cell “‘ with slightly rounded ends” “80 » long 
and 40 » broad,” and (say) only 10 thick, would con- 
tain some sixty of even the large collar-cells of Grantia 
compressa. Geo, P, BippeEr. 
Cavendish Corner, Cambridge, December 14. 
Mr. Brpper is perfectly right. The Amcebz de- 
scribed by Mr. Orton are far too large to be meta- 
morphosed collared cells or even young amoeboid germ 
cells. The only cells in the sponge (Grantia com- 
pressa) which compare with them in size are the full- 
grown oocytes, and although these are amceboid and 
put out long pseudopodia, it is scarcely likely that 
they would find their way into the gastral cavity, as 
I have never seen them except in the mesogloea be- 
tween the chambers. My data, from which the actual 
size of the amoebocytes could be calculated, were not 
at hand when I wrote my letter, and as I had been 
working with a magnification of 1650 diameters, my 
ideas of a “rather small’’ Amceba had come to differ 
considerably from Mr. Orton’s. Knowing how 
abundant ameebocytes frequently are in the flagellated 
chambers of the sponge it seemed almost certain at first 
sight that any obtained from the gastral cavity would 
be of the same nature, but evidently I was mistaken, 
and I am much obliged to Mr. Bidder for directing 
my attention to the fact. ArtHUR Denby. 
University of London, King’s College, 
December 16. 
Reversibility of Ferment Action. 
In Nature of December 4 last there is a letter from 
Sir Lauder Brunton, correcting a misstatement in a 
former issue in connection with a paper by Prof. 
Bourquelot on the reversible nature of ferment action. 
Sir Lauder Brunton’s letter points out a mistake that 
might have been prejudicial to me; but your original 
article was not quite fair also to Prof. Bourquelot, for 
he, so far from claiming priority for himself, gave 
me in his paper full recognition. 
Since I first showed that the action of a ferment was 
a reversible one, many observers have done confirma- 
tory work. The earliest to do so were Profs. Kastle 
and Léwenhart, of the United States, and among the 
more recent, Prof. Bayliss in this country has done 
valuable work. 
I am glad that Prof. Bourquelot by his own good 
work has become convinced. 
ARTHUR CRorT Hitt. 
169 Cromwell Road, S.W., December 19. 
NO. 2304, VOL. 92] 
NATURE 
479 
THE ORIGIN OF CLIMATIC CHANGES. 
feo discussion of meteorological observations 
shows clearly that climates undergo varia- 
tions of short duration, but such records as the 
presence of old lake beaches and the existence of 
well-marked glacial moraines, and other geological 
evidence distinctly point to climate changes cover- 
ing long intervals of time. The evidence is not 
sufficient to characterise the variations as periodic, 
but the ice ages are sufficient to point to times 
when the conditions reached were extreme. 
What may reasonably be assumed to be the 
chief established facts about such extensive 
changes may be summed up briefly as follows :— 
Climatic changes were several, and probably many. 
Similar simultaneous changes occurred over the 
whole earth, or, in other words, it was warmer 
or colder over the whole earth simultaneously. 
These times of warmth or coldness were unequal 
in intensity and duration, and of irregular occur- 
rence, and, lastly, they have taken place from 
very early, if not from the earliest geological age 
down to the present. Numerous theories, both 
probable and improbable, have been suggested 
from time to time to account for the origin of such 
world-wide changes, and while each has its ad- 
vocates, perhaps only three may be said to claim 
attention to-day. These may be briefly stated as 
the Eccentricity Theory (Croll), depending on the 
eccentricity of the earth’s orbit; the Carbon 
Dioxide Theory (Tyndall), based on the selective 
absorption and variation in amount of carbon 
dioxide; and thirdly, the Solar Variation Theory, 
on the assumption of solar changes of long dura- 
tion. A new theory, which may be called ‘The 
Volcanic Dust and Solar Variation Theory,” has 
recently been put forward by Prof. W. J. 
Humphreys,! under the guarded heading, “ Vol- 
canic dust and other factors in the production of 
climatic changes, and their possible relation to 
ice ages.” 
The author carefully points out that the idea 
that volcanic dust may be an important factor in 
the production of climatic changes is not new, 
but “though just how it can be so apparently has 
not been explained, nor has the idea been specifi- 
cally supported by direct observation.” He re- 
marks also that while the pioneers regarded the 
presence of volcanic dust in the atmosphere as an 
absorbent of radiation, and so lowered the earth’s 
temperature, modern observation suggests the 
opposite effect, namely, the warming of the earth’s 
surface. 
In putting forward his views of the action of 
dust, Prof. Humphreys proceeds first to indicate 
that the dust that is effective is that which is 
situated in the atmosphere in the isothermal 
region or stratosphere. He then enters into the 
question of the size of the particles and probable 
time of fall, and concludes that particles of the 
size 1°85 microns in diameter would take from 
one to three years to get back to the earth if 
1 Journal of the Franklin Institute. August, 1913, vol. clxxvi., No. 2, 
p; 131; also Bulletin of the Mount Weather Observatory, August, 1913, vol. 
vi,, part 1, p. 1 
