370 
means improving the crop by choosing wheat that is 
immune from the effects of incidental causes which are 
part of the natural order and used to be instrumental 
in depressing the market yield. Moreover, when 
wheat was cheap there was a disposition only to sow 
it in the most favourable land, to withdraw the rest 
from wheat-cultivation, and thus to raise artificially 
the average yield per acre. 
Considering all the circumstances, even as they were 
in 1906, it is surprising that any suggestion of law 
should come out of the figures at all. Improved know- 
ledge among farmers may easily now have introduced 
variations which will form a systematic error in the 
comparison of facts with the calculations of either 
“theory ’’; consequently the investigation means _ rather 
more than comparing figures. The mere repetition of 
the process that was good enough for 1904 may be 
illusory in 1917, for causes which were not inherent 
in the original figures. NaPIER SHAW. 
A Frost Thistle: A Beautiful Effect of Freezing. 
Tue frost flower here photographed was entirely the 
result of a chance experiment, but it was so beautiful 
that it would be well worth repetition and detailed 
study. 
So far as I can see, the sole factors necessary for 
the production of such an effect are a small amount 
of garden mould left standing in a little water (about 
an inch in depth) in a small glass jar, and frosty 
weather. In this particular case the vessel was left 
out of doors on a window-sill during a recent frosty 
night in-a state of tranquillity save for the occasional 
shakings caused by vehicles passing over the bridge 
be low. 
In the morning the 
was intact, 
the 
water was frozen solid; the glass 
the ice having expanded upwards, doming 
surface. Within the ice cylinder was a wonder- 
fully perfect representation of a thistle flower, most 
delicately fashioned in gleaming threads of ‘silvery 
whiteness and of exquisite beauty, all emanz iting from 
a fluffy-looking, opaque, central, domed nucleus. 
In reality the frei ads were fine curved threads of 
gas (? air) radiating through the clear ice. As shown 
in the figure, those be ‘low curved downwards, those 
above upwards, for all the world like lines of force 
round a magnetic pole, 
NO. 2463, 
but demonstrated by capillary 
VOL. 98] 
NATURE 
[JANUARY II, I917 
tubes in ice. On closer examination I was, I believe, 
able to discover another essential feature in the pheno- 
menon in the form of tiny specks of mud, one at the 
peripheral end of each gas-tube. 
I submit the following explanation of the frost 
thistle. 
It must be assumed that as freezing proceeds from 
without inwards, the gas-tubes also grew centripetally- 
The tiny particles of earth we believe to have deter- 
mined the points of origin of minute gas bubbles. 
When the first shell of ice was formed, these bubbles. 
would naturally, by the expansion of the ice, tend to 
be squeezed and compelled to elongate, and then to 
move in the direction of least resistance—i.e, inwards. 
and towards the centre of the vessel. In other words, 
these silvery threads, curving, as they do, upwards from 
the bottom and downwards from the tov, are graphs 
which indicate the progress of the congelation. 
When the congelation had reached to about one-third 
of the radial distance to the centre, some change 
appears to have occurred, for the central ice-mass was 
no longer clear, but of a milky opaqueness, within 
which the gas-tubes could be no longer followed by 
the eye. This we attribute to the sudden solidification 
of a confined residual volume of liquid of enhanced 
salinity, which, at the moment of its change of state, 
yielded up its dissolved gases in countless bubbles of 
the minutest size. These, probably uniformly distri- 
buted throughout the cefitral ice, produced its cloudi- 
ness. : 
May I add that this example of natural magic grew 
within a few yards of the site of Roger Bacon’s study 
on Folly Bridge at Oxford? R. T. GuNTHER. 
NATIONAL RECONSTRUCTION. 
i is not too much to say that of all the subjects 
which claim careful consideration at the 
present time of discussion as to Imperial recon- 
struction, none is more important than education. 
It is true that the consequences of any change for 
the better or worse in educational matters will 
affect more directly the next generation than the 
present, but the clarification of men’s minds and 
the settlement of a course of action in this direc- 
tion are urgently desirable. For it is evident that 
opinion is still much divided as to the aims which 
ought to be kept in view, and until such divisions 
are practically healed the present wasteful con- 
flict will go on. 
The discussion which has been carried on during 
so many years by the partisans of classical studies 
on one hand, and the supporters of science on the 
other, is an indication that there is still much 
misunderstanding and exaggeration on both sides. 
The extremists on one side contend that Greek is 
an essential element in a liberal education, and 
talk of physical science as “gross materialism,” 
while some of the extreme opponents of classical 
studies are not content with dropping Latin and 
Greek, but would turn schoolboys into technical 
chemists. It is to be hoped that the people with 
more moderate views, who fortunately seem to 
form the majority, will arrive before long at a 
generally acceptable compromise whereby the 
interests of a truly liberal education may be 
secured. 
The advocates of the classical system have 
shown in recent utterances a moderation whicl 
