402 
air current vary as the square of the relative velocity, 
the mean reaction is greater than that due to the 
mean velocity considered as steady. 
HERBERT CHATLEY. 
Chinese Government Engineering College, 
Tangshan, North China, May 24. 
Weather Forecasts in England. 
Mr. MALLock, in giving his reasons for believing 
that correct weather forecasts are not likely to. be 
possible even for twenty-four hours in advance, 
touches upon many very debatable meteorological 
theories. 
His diagram purporting to show the surface wind 
currents for an earth, the surface of which is level 
and uniform, requires for its prediction a much better 
knowledge of the actual cause of wind distribution 
than we possess at present. Indeed, at the present 
time, it would appear that the wind conditions he 
shows are more nearly those of the northern than the 
southern hemisphere, and rather are the result of the 
irregular distribution of land, sea, and mountain than 
to uniform surface conditions. In the southern hemi- 
sphere the conditions, as near the equator, approxi- 
mate more to belt than to cyclonic conditions. 
An inspection of the daily weather charts issued 
by the Meteorological Office will also show that the 
general directions of the winds over the northern 
hemisphere are by no means as Mr. Mallock shows. 
A cyclone is a much more complex affair than the 
whirls of his figure. Cyclones are generally rather the 
result of the common action of several winds moving 
in different directions. Not only is this the case, but 
we have no accepted theory as to the cause of cyclones 
and the source from which they derive their energy. 
If it were a simple matter of the passage and rapid 
appearance and disappearance of cyclones, as Mr. 
Mallock supposes, I take it that the weather condi- 
tions would be rapid alternations of sunshine, cloud, 
and rain.. But such is not the case. We have long 
periods of fine weather, long periods of wet, un- 
settled weather, and spells of heat and cold. We must 
recognise the fact that on the earth we have regions 
where the weather conditions vary regularly with the 
seasons, and we also have insular and oceanic weather 
conditions. The boundaries of these areas are not 
always the same. The one is apt to encroach upon the 
other, and it is probable that by obtaining a know- 
ledge of such general movements, weather forecasting 
for considerable periods of time will be possible. 
So long as the old ideas of cyclones and anti- 
cyclones held sway, weather predicting really seemed 
hopeless; but fortunately we find that these old 
theories, though expressing important truths, require 
considerable modification in detail. Mr. Mallock’s 
contention that useful forecasting will never be pos- 
sible seems premature in face of the fact that there 
are so many things taking place in weather changes 
the theoretical reasons for which are unknown. 
With improved weather charts will come a better 
knowledge of the theory of cyciones and anticyclones. 
However, it may never be possible to predict, from the 
to-be-discovered laws of the winds, the course of 
weather changes with the certainty the movements 
of the members of the planetary system can be pre- 
dicted by the application of Newton’s laws. 
R. M. DEELEY. 
Abbeyfield, Salisbury Avenue, Harpenden. 
The Thunderstorm of June 14, at Dulwich. 
My observations on the thunderstorm of Sunday, 
June 14, at Dulwich, may perhaps be of interest. 
Thunder was first heard a little before 12.30 p.m., 
and lightning was seen from about 12.45. These 
NO:2320; VOL. 93 | 
NATURE 
[JUNE 18, 1914 
continued more or less throughout the afternoon until 
quite 5 o’clock, the lightning being very brilliant and 
rather frequent. Heavy rain iell from 12.50 until 
I.J0, and from 1.15 to about 2.20. Some white hail 
fell about 1.45. 
At 2 p.m. there was a heavy fall of big hailstones 
as large as marbles, which lasted about five minutes. 
Many of these hailstones were like large acid tablets, 
about an inch long, half an inch broad, and more 
than a quarter of an inch thick. The hailstones were 
composed of perfectly clear ice, and did not contain 
any white opaque substance. Hailstorms are usually 
accompanied by gusts or squalls of wind; in this 
storm, however, there was but little wind. 
When the big hailstones fell the leaves were torn 
off the trees, and so the pavements immediately be- 
neath them became quite green with the fallen leaves. 
The heavy rain, however, quickly washed these away, 
so that they were carried-into the gutters and soon 
stopped up the drains, with the result that the roads 
were flooded. 
A minute or two after the big hailstones had fallen, 
a mist arose above the roads and pavements to a 
height of about 4 ft. This clearly showed how the 
fogs were formed near the Banks of Newfoundland 
owing to the mixing of the cold and warm sea cur- 
rent. 
Rain came on again about 3.15, and continued until 
-m, 
“ it was not able to get to my rain-gauge in Alleyn 
Park until atter 5 o’clock, as the lawn was flooded 
and the water had not subsided sufficiently for me to 
get into the garden. I found the rainfall to be 
2-15 in., and of this amount I believe that about 1-60 
to 1-75 in. must have fallen in three-quarters of an 
hour, from 1.30 p.m. to 2.15 p.m. 
Wn. Marriorir. 
Royal Meteorological Society, 70 Victoria Street, 
London, S.W., June 16. 
A Dual Phenomenon with X-Radiation. 
SINCE our paper on the ‘‘ X-Rays and Concentra- 
tion,’’ and our exhibition of models and negatives at 
the annual general meeting of the Roéntgen Society 
on June 9, we have obtained further results which 
favour the hypotheses then suggested. 
For instance, if a radiograph be taken at any inci- 
dence (except o° and go®°) of a ring of rectangular 
cross-section made in ebonite, its circular edges will 
be distinctly visible as black and white semi-circles. 
These alternate for the top and bottom outer rings, 
and they are in the reverse order for the inner circles. 
These differences were predicted from the generalisa- 
tion we gave in the paper. We think it would be 
advantageous to repeat the conclusion of the paper for 
those who were not present at the exhibition :— 
‘‘Generalising our results, it would seem that when 
X-rays are incident (or emergent) simultaneously upon 
two surfaces having a common boundary, this will be 
marked by a white or black band according as the 
dihedral angle of the solid is greater or less than 180°. 
If, however, the rays are incident upon one of the 
surfaces only, and emergent from the other, the order 
is reversed. In the third case, where the rays are 
incident upon one surface but parallel to the other 
(as with single laminae) the two bands appear in close 
association, and are observable with difficulty without 
the aid of suitable magnification.”” Tangential radia- 
tion has given a black or white band according as the 
surface was convex or concave. 
I. G. Rankin. 
W. F. D. CHAMBERS. 
90 Gordon Road, Ealing. 
