
Suly 20, 1871 | 
NATURE 
223 

entered by any insect of considerable size, which must inevitably 
have carried away the pollinia with it. The fact that the Bee 
Orchis, the most “imitative” of all our native plants, is never 
visited by insects, is a very suggestive one. If, as might well 
have been assumed, the object of the ‘‘mimicry” is the attrac- 
tion of bees, the device appears to have signally failed. 
London, July 17 ALFRED W, BENNETT 
Saturn’s Rings 
As Lieut. Davies has thought it necessary to refer to your 
remarks about the satellite theory of Saturn’s rings—and in so 
doing has named my work upon Saturn (which you had ov/y re- 
ferred to without naming) it may be as well for me to mention, 
that Inowhere in that work claim the theory as mine—and that, 
whenever I have seen it referred to as mine, I have as publicly as 
possible disclaimed all title to it. 
Permit me to add, that, whatever opinion we form of Lieut. 
Davies’s views, he deserves our thanks for bringing out a treatise 
so full of work, from cover to cover, as his ‘* Meteoric Theories.” 
Such examples are a good deal needed in these days. 
8, Wellington Villas, Brighton RICHARD A. PRocTOR 
Ocean Currents 
I FIND that Dr. Carpenter does not consider his experimen 
probative. Judging from the air of triumph with which, both in 
his lectures and writings, he has announced its success, I had cer- 
tainly imagined that he did. But if not probative, what is it ? 
Dr. Carpenter says it is only intended to be illustrative. What 
does it illustrate? It does not illustrate any currents formed in 
the ocean by differences of temperature ; for it does not illustrate 
the differences of temperature to which he attributes these cur- 
rents. In his letter in NATURE of July 6, he proposes an un- 
wieldy modification of his former well-known experiment, but 
which still, I would submit, in no way avoids the difficulty to 
which I have called attention. He describes a strong freezing 
mixture applied to the surface through one-tenth of the length of 
a trough half a mile long, and heat applied to the surface also 
through one-tenth of the length, measured from the other end: 
between the cold and the hot surface there is, then, an inter- 
vening space of four-tenths of a mile, or 2,112 feet ; that is to 
say, there is a thermometric gradient of about 50° in 2,000 feet, 
or I° in forty feet. This is small enough, and we may perhaps 
doubt whether such a gradient could give rise to any appreciable 
movement ; but it is 15,000 times greater than the gradient ob- 
served in the ocean, which is about 1° in 1oonautical miles ; and 
any movement shown by an experiment which, in its details, 
bears no reasonable proportion to the reality, cannot be accepted 
as an illustration of a movement in the ocean. 
Mr. Proctor, in the same way, speaks of his proposed experi- 
ment as an illustration ; and, in the same way, I would say that 
the distortion produced by magnifying 6,000,000 times that par- 
ticular detail on which he wishes to lay an emphasis, precludes 
our accepting it as an illustration at all. Mr. Proctor says that 
it is intended specially to throw light on the easterly and 
westerly movements ; it is surely unnecessary for me to point out 
to him that any easterly or westerly movements, as illustrated in 
a cylinder such as he describes, revolving continuously and uni- 
formly, are direct consequents of the outward or inward move- 
ment due to the differences of temperature, and are, therefore, 
in the strictest sense, dependent on the thermometric gradient. If, 
with a thermometric gradient of sy/oua Of a degree in one foot, 
and with an angular velocity of 360° in 24 hours, Mr. Proctor 
succeeds in showing any appreciable movement, I and (I think I 
may add) many other readers of NATURE will be glad to learn 
the result. But this is, after all, the point I raised in my last 
letter (NATURE, June 29), and which Mr. Proctor considers 
would require many columns for its full discussion, I do not 
myself see that there is any room for discussion at all ; and any 
difference of opinion that may exist can only be met by experi- 
mental demonstration, 
Dr. Carpenter appears to wish to support his theory on 
“authority,” and especially on that of the recent letter of Sir 
John Herschel, This is a point on which I touch with great re- 
luctance; but I would point out, in the first place, that 
‘‘authority” in matters of science carries very little weight ; 
and, secondly, that Sir- John Ierschel, in the letter referred to, 
merely admits what he and everyone else have all along admitted, 
that hot water and cold, in juxtaposition, will establish a circu- 


lation. It was not for him, in a letter of private courtesy, to 
enter again on a discussion of the infinitesimal nature of the 
gradients—a discussion which he had already worked out very 
fully in his ‘* Physical Geography.” 
But, leaving this consideration on one side, I maintain that, at 
the present time, the ozs proband: rests with the supporters of 
the temperature theory. Its opponents have offered what is, at 
any rate, a rational, consistent, and tolerably complete explana- 
tion of all the known ocean currents ; and they say, in so many 
words, that the explanation offered, in accordance with the theory 
of temperature and specific gravity, is neither complete, nor con- 
sistent with itself or with geographical observation, The theo- 
retical objection of the infinitesimal nature of the thermometric 
gradients and of the differences of specific gravity, which has, 
indeed, formed the subject of these letters, is not one which I 
was inclined to put forward in any prominent degree. I preferred, 
and still prefer, to base my objection on the utter discrepancy 
between fact as observed, and fact as described by Captain 
Maury and Dr. Carpenter, in accordance with their theory. 
Ihave elsewhere dwelt on this at great length, and do not 
intend to go over the same ground here, even if you were 
willing to afford me the space to do so; but this discrepancy, 
which actually and very markedly exists, does call attention to 
the thermometric gradients in the ocean ; and when we find the 
same discrepancy between observation and description in the case 
of aérial currents, it leads to the conclusion that the infinitesimal 
nature of the thermometric gradients is as sound an objection to 
the temperature theory of atmospheric circulation, as it is to the 
temperature theory of oceanic circulation. I refer here to the 
last sentence but one of Mr. Proctor’s letter. The last sentence, 
I must confess, I do not understand. I do not see what effects 
solar light can produce, or even be supposed to produce, on the 
depths of ocean, to which no light penetrates; still less do I see 
how to integrate them. 
J. KK. LauGuton 

Formation of Flints 
In your report of the discussion that followed the reading of 
my paper on Flint, before the Geologists’ Association on June 
2nd, Prof. Morris is said to have asserted that the views I sug- 
gested were first propounded by Dr. Brown of Edinburgh. I 
think the Professor must have been slightly misrepresented in 
this ; at all events I must most decidedly decline to be coupled 
with Dr. Brown, or to allow myself to be associated with his 
very remarkable statements. These may be found in the Trans. 
Roy. Soc. Edinb., vol. xv. He asserts that carbon is trans- 
mutable into silicon; at p. 229 he says, ‘‘ Carbon and silicon 
are isomeric bodies, and that the former element may be converted 
into a substance presenting all the properties of the latter.” At 
p- 244, ‘* 3°04 grains of silicic acid were extracted from 5 grains 
of paracyanide of iron ;” at p. 245, ‘* 5°4 grains of silicic acid 
were procured from 30 grains of the ferrocyanide of potassium,” 
and ‘‘ there were obtained 9, 334 grains of silica from 3,240 grains 
of ferrocyanide, although some of the product was lost in two of 
the operations.” The view I advocated as explanatory of the 
formation of flints was the sadstitution of silicon for carbon, not 
a transmutation, and I distinctly showed the source from which the 
silicon was derived. Dr. Brown’s statements are so extraordinary 
that I could scarcely believe them serious. I find, however, in the 
same volume of the ‘‘ Transactions” that they were most patiently 
examined and confuted by Dr. George Wilson and Mr. John 
Crombie Brown, and they say, “ We tried the greater number of 
Dr. Brown’s processes, and rejected them one after another with- 
out pursuing their investigation further, on finding they would 
not yield quantitative proofs of the conversion of carbon into 
silicon. The limited time, which from various circumstances 
we could devote to the subject, obliged us to follow this course ; 
and the confident expectation we entertained till a recent period 
that each new process would supply what the rejected ones had 
failed to afford, led us to neglect noting many particulars of our 
early trials which otherwise we should have recorded. . . . In 
conclusion, we need scarcely say that we have been unable to sup- 
ply any proof of the transmutability of carbon into silicon.” 
I have one more objection to make to the report. I did not 
say that flints were merely silicified sponges. I believe that such 
is the case with some flints, but certainly not with all. I hope 
you will find space for this rectification of manifest errors. 
M. HAWKINS JOHNSON 
379, Euston Road, July 11 
