8 NATURE 
[May 4, 1871 

arch in the morning, and the pale light seen shooting across it, 
were connected with the same phenomenon.” 
I have just been informed by a friend whose veracity I would 
be the last to question, that he saw a very faint arch in the 
eastern sky on the afternoon of the roth inst. (about 4.30 P.M.). 
There were no clouds near it, while the background was a beau- 
tiful azure. The colour of the arch was of a much fainter blue, 
or, as he calls it, ‘‘a whitish blue,” and was almost a perfect 
semicircle. I have not the least doubt that it was a ‘‘ daylight” 
aurora ; it must be remembered that on the previous night there 
was a most magnificent aurora borealis. 
In conclusion, after carefully examining the facts contained in 
the various communications to your journal, as well as those 
which I have collected, I cannot see any reason for doubting the 
possibility of the aurora borealis being seen by daylight. It will 
be interesting to know what those daylight phenomena are, if not 
auroras. JOHN JEREMIAH 
Red Lion Street 
The Irish Fern in Cornwall 
Your correspondent having, much to my regret, so exactly 
informed the ‘‘ruthless collectors” where they are to look for 
this fern, I fear that after the ensuing autumnal ravages not a 
single frond will be left to speak for itself. Permit me, 
therefore, to state that the fern unquestionably grows, or did 
grow, at the place indicated, and was, I believe, first recognised 
in 1866 by Mr. Robert Were Fox, I’.R.S., who has a plant he 
thus obtained still growing in his fernery at Penjerrick near this 
town. W. P. DyMonD 
Falmouth, April 29 
The Prevalence of West Winds 
In a letter with this heading in Nature for February 16th, 
Mr. Murphy has very roundly objected to certain views which I 
have put forward regarding the predominance of westerly winds. 
In the paper read before the British Association, to the abstract 
of which he refers, and which was itself little more than a 
résumé of the propositions maintained at greater length in my 
‘« Physical Geography,” reviewed by “A. B.” in NATURE for 
March 16th, my object was not so much to show that westerly 
winds predominated in volume over easterly winds, as to show 
that all prevailing winds, not westerly, may be properly con- 
sidered as deflected or secondary currents of air, and that more 
especially the trade winds may be so considered. I have sup-* 
ported this view by a detailed examination of the geographical 
circumstances, habitudes, and characteristics of the principal 
winds ; but to have included every local exception—as ‘‘ A. B.” 
seems to consider I ought to have done—would have required 
more time than even the most industrious can spare, an amount 
of special topographical knowledge which is practically unattain- 
able, and would have had no important bearing on the main 
question. I may go even further. I may say that, from a 
general point of view, isolated local registers have no value at 
all, unless the method of observing and the position of the vane 
are distinctly made known. It would be perfectly easy to name 
a dozen localities in Wales, in the Lake District, or in Scotland, 
where a vane would show a prevailing wind widely different from 
the W.S.W., which, however, we have no difficulty in accept- 
ing as the prevailing wind of the country ; even at Liverpool the 
prevailing wind has been observed to be W. N. W., and at Valentia 
there is a marked difference between the wind in the northern 
and southern entrance. In Mr. Buchan’s paper in the Trans- 
actions of the Royal Society of Edinburgh, December, 1869, I 
find that at Irkutsic the wind is almost always due north, or due 
south, would “A. B.” imply that the Irkutsk observations 
afford any information as to the prevailing wind of Siberia? 
In another paragraph, ‘‘ A. B.” considers that the preponde- 
rance of westerly winds cannot be very great. So far as the area 
over which westerly winds blow is concerned, I would partly 
agree with him ; taking into account the constant interruptions 
to the west winds in the temperate zones, and on the other hand 
their frequent intrusion into latitudes considerably below 30°, 
more especially in the Pacific, and their prevalence during several 
months of the year over a large portion of the Indian Ocean, Iam in- 
clined to reckon the ratio of the area of westerly winds to the area 
of easterly winds as approximately 13:10. But such an estimate 
* Jameson’s Journal, quoted in the “‘ Arcana of Science and Art” for 1828, 

does not in any way include the velocity of the wind ; and since 
the velocity of the west winds of temperate latitudes is, in the mean, 
about double that of the easterly winds of tropical, it would follow 
that the respective volumes of the winds bear to each other a much 
larger ratio, which, allowing freely for every reasonable reduc- 
tion, cannot be less than 2:1. And this estimate still relates 
only to the lower strata of the atmosphere, through a height pro- 
bably not exceeding 12,000 feet. Our knowledge of the winds 
above that height is very limited ; but since, wherever observa- 
tion extends, it points out to us 2 strong, frequently even a violent 
west wind, it seems to me that we have a fairly presumptive 
proof that the prevailing direction of the upper current is from 
the west. I base this belief entirely on the evidence which we 
have, defective as it is and as it almost necessarily must be; to 
explain the fact by a reference to a difference of barometric 
pressures, concerning which we have positively no evidence at 
all, is a task which I most willingly leave to my reviewer. But 
if, as I have maintained, we may fairly assume that the upper 
current has an almost invariable direction from the west, and 
that too with a comparatively high velocity, the ratio of the 
volumes of westerly and easterly winds is enormously increased, 
and if the upper part of the air, being quite half of the 
whole, is moving from the west with a mean velocity of 40 miles 
an hour, then, as we have already taken 20 miles, or the velocity 
of the trade winds, as the standard or unit of reference, we have 
the ratio of westerly to easterly winds as about 6; 1. 
The question which Mr. Murphy has suggested no doubt here 
arises: Must not this preponderance of westerly winds affect the 
rotation of the earth? I have throughout maintained the exis- 
tence of this preponderance solely by geographical proof, and 
conceiving that the evidence is conclusive, whilst no meteoro- 
logical theory points to any explanation of it, I am compelled 
to attribute it to the action of some force external to the earth ; 
possibly, as I have endeavoured to show, to the attraction of the 
sun, moon, and other heavenly bodies ; possibly also to some other 
force, magnetic ormeteoric, of whose action wehave as yet no know- 
ledge or understanding : but supposing, as I do, that the force which 
produces this motion is external to the earth, it is impossible to 
avoid the conclusion that it does tend to increase the earth’s 
velocity of rotation. On the other hand, there are forces, ad- 
mitted by all naturalists, in constant action, which tend to de- 
crease the velocity of rotation ; and a certain amount of wonder 
that the decrease so caused is so small as observation proves it 
to be is implied, rather than expressed, in our most valuable 
works on Natural Philosophy. If it is impossible in the pre- 
sent state of our knowledge to show exactly what such decrease 
is and ought to be, it is certainly impossible to say that it is not 
to some extent counterbalanced by a contrary tendency towards 
an increase, such as I have shown probably exists. At any rate, 
I know of nothing connected with the rotation of the earth 
which in any way controyerts or affirms the proposition which I 
have put forward, based on geographical evidence only. 
I had written this before seeing Mr. Murphy’s second letter 
on the subject in NaTuRE for March 30, but as he has in it 
merely repeated his former arguments, it is unnecessary to notice 
it more particularly, J. K. Laucuron 
Royal Naval College, Portsmouth 


SUBMARINE TELEGRAPHS 
We may possibly be within the memory of some persons 
that, about the year 1840, Sir C. Wheatstone first 
conceived the idea of transmitting messages under the 
sea, and practically carried out at that time the first sub- 
marine telegraph cable. Selecting Swansea Bay, South 
Wales, as the chosen spot for his experiment, the great 
inventor sat in an open boat, about three miles from the 
Mumbles Lighthouse, with the lighthouse keeper as his 
assistant. A conducting wire, insulated with hemp and a 
resinous compound, served as the electric communication 
between his open boat and the shore. It is from the 
successful results of this first crude experiment, and 
Wheatstone’s investigations into the laws that regulate 
the transmission of electric currents through metallic con- 
ductors, published shortly afterwards in the Philosophical 
Transactions of the Royal Society of London, that our 
present system of the testing of submarine cables is based, 
