382 
NATURE 
preliminary paper, and that Mr. Lockyer intended to follow up 
and did follow up his suggestion with the requisite obseryations. 
But at that time neither Mr. Lockyer nor myself knew to what 
extent the spectroscope would throw light upon these red flames. 
What service I did wasin stating my opinion that those red 
flames were probably gases, while the suggestion as to how to 
detect them was due to Mr. Lockyer. - Had the red flames 
proved to be solid particles, the spectroscope would have afforded 
only meagre negative evidence of their existence. 
Our ignorance on this point suggested to us the propriety of a 
query. It was only in this respect that the query was ambiguous, 
that is to say there was no doubt that the method suggested by Mr. 
Lockyer would throw a great deal of light upon the red flames 
if they proved to be gaseous, but the only doubt in our minds 
was whether or not they were gaseous. 
4. I have tried as well as I can in justice to both of us, to 
remember and reproduce what took place in the conversation 
in 1866 between Mr. Lockyer and myself, and to show the 
reasons for the form in which Mr. Lockyer’s suggestion was put. 
Probably Mr. Huggins announced it afterwards in a more com- 
plete form, and probably it has since been announced in a yet 
~ more clear and complete form, if this be possible. For we know’ 
that as a rule discoverers and inventors have no great power of 
expression, and if the prize is to be given for the clearest 
possible utterance of a truth, it will be very seldom won by the 
discoverer, but will very frequently be obtained by the popular 
writer. Neyertheless I fail to see that Mr. Lockyer’s original 
query was at all ambiguous in the sense that Mr, Proctor 
suggests. How, I should like to know (adopting the words of 
the query), could the spectroscope afford us evidence of the 
existence of the ‘‘ red flames at other times than those of a total 
eclipse, unless by dispersing the reflected light.” 
5. Mr. Proctor asks, To what end are we to inquire whether 
Mr. Lockyer would or would not have detected the lines without 
the information derived from the eclipse observations? As far 
as I can understand the question I quite agree with Mr. Proctor. 
I do not think the inquiry ought ever to have been made. 
When, however, it was suggested that Mr. Lockyer derived aid 
from the Indian observations it was surely allowable for him 
to deny the iniputation. 
6. I have sometimes thought that discussions too frequently 
arise from the attempt to compare together the labours of 
different men, when all that is necessary is a statement of facts 
and dates. It isa matter of fact that the Indian observers at 
a particular date and under particular circumstances, made 
certain observations and derived certain results. It is likewise a 
matter of fact that Mr. Lockyer, ata date slightly later and 
under ceriain other circumstances, made observations of another 
kind, from which he also derived certain results. Different 
minds are differently constituted ; one will think more of the 
Indian observations, another of those of Mr. Lockyer. But 
why should the two be compared together, unless some good 
object is to be gained by the comparison? 
7. Now I cannot see why Mr. Proctor in his letter should 
have made the comparison at all, but since he has done so, I 
must be allowed to object to his method of makingit. ‘‘ Surely,” 
he says, ‘‘on this matter we must assign Mr. Lockyer only the 
credit arising from the fact that, possessing an instrument which 
made the work child’s play, he saw the lines by the method de- 
scribed by Huggins nine months before in detail, and depending 
on a principle which Huggins had stated fully two years and nine 
monchs before.’ I have already endeavoured to dispose of 
the latter part of the statement, and indeed Mr. Huggins has dis- 
posed of it himself; but with regard to the first part of it, I 
conceive that the possession of an instrument which made the 
work child’s play, forms one element of the credit due to Mr. 
Lockyer. At first his instrument was defective and unable todo 
what he wished, but his conviction that something was to be 
made out of the sun, if examined by a powerful spectroscope, 
was so strong, that after much delay on the part of the optici.n 
employed, and sundry other discouragements, he at last pro- 
cured {or himself an instrument with which he saw the red 
flames at the very first trial. 
8. I should not have alluded to the concluding paragraphs of 
Mr. Proctor’s letter were it not written by one who holds a high 
official position in the Royal Astronomical Society. To my 
mind it is most deplorable that the secretary of this society 
should conceive himself at liberty to make in a public journal 
unsupported statements reflecting discreditably upon a distin- 
guished member of that society. It is bad enough when two 
private men of science abuse each other, but it is not to be tole- 
rated when a hizh official of a society of standing descends into 
the arena. If he insists upon doing so it is surely not unreason- 
able to request that he will in the first place divest himself of his 
robes of office. 
For my own part [ have thoughtythat Mr. Lockyer has 
attached only too much importance to the little help I gave him 
when we conversed together in 1866. 
BALFouR STEWART 
Mr, Mallet’s Theary of Volcanic Energy 
WILL you allow me to make a few remarks upon Mr. David 
Forbes's critique, which has but just now met my eye, though 
published in NATURE of February 6 last, upon my translation 
of Prof. Palmieri’s ‘‘ Incendio Vesuviano,” and more especially 
“upon that gentleman’s animadversions upon my views as to ‘f the 
true nature and origin of volcanic heat and energy,” a brief and 
incomplete account of which I have given in the ‘f introductory 
sketch” prefaced by me to that translation. ' 
Mr. Forbes commences (p. 260) with an important error as to 
a matter of fact, by referring to ‘* Mr. Mallet’s Dynamical Theory 
of Volcanic Energy,” as published in the Proceedings of the 
Royal Society for 1872. 
My paper as above was read in abstract only in June last to 
the Royal Society, and being reserved for probable publication 
in the Phil, Trans., nothing but the most meagre and incomplete 
abstract has appeared in the Proceedings of the Royal Society. 
I have given a somewhat fuller, but still most mcomplete, ac- 
count of itin my ‘f introductory sketch” above referred to, My 
paper, and the full statement of my views, with the proofs which 
give them validity, have thus as yet never been published at all, 
nor even verbally stated publicly, the paper beiag still—afcer 
eight months, I regret to say —in the hands of the referees. 
When published—as the paper in some form will no doubt be 
—Mr. Forbes will find that fis objections—so far as I can gather 
anything tangible from their statementin Narure—have been 
anticipated, and I believe completely answered, in my paper, 
along with others, better founded, because based on fact, which, 
as it appears to me, Mr. Forbes’s objections are not. 
Mr. Forbes uses ‘‘ theory” and ‘‘ hypothesis” as though quite 
the same (p. 260). My hypothesis is simply undeniable, being no 
more than that our globe is a terr-aqueous planet subject to secular 
refrigeration; and upon that hypothesis I have built up my 
theory, that the evolution of volcanic heat is a necessary result, 
upon acknowledged physical lawsof such refrigeration; and that 
from such heat so evolyed—as the Z7?mum mobile—come in 
train all the other recognised volcanic phenomena: chemical, 
as in the fusion and combination of the constituents of rocks 
into definite and indefinite compounds, decomposition of many 
solid, liquid, and gaseous bodies ; mechanical in the elevation 
and throwing out at volcanic vents of all or any of these: water, 
air, and the chemical elements known to exist in the crust of our. 
earth being the only conditions needed, in addition to heat, to 
account for all that we know as to volcanic phenomena, as now 
active in our planet, . 
I claim to have been the first to apply ** measure, number, 
and weight ” to volcanic theory ; and when men of science gene- 
rally shall have had access to my statements, I trust it will be 
admitted that I have not shrunk from rigidly testing by caleula- 
tion the adequacy of the source I assign for volcanic heat, nor 
ofthe mechanism through which its subsequent effects are pro- 
duced, as seen in volcanic phenomena. Iam at the disadvan- 
tage that I cannot expect to cumber your pages by reference to 
those proofs—they are the less necessary here, however—inas- 
much as my reviewer, though affecting to discredit the adeq 
of the origin I assign for the ‘‘ quantity of heat requisite to melt 
up such vast volumes of rock matter as are known to proceed 
from volcanoes,” does not present a single argument against it, 
and, in fact, appears unwillingly to admit it. He however pro- 
ceeds to object generally to my views by the following state- 
ments. They are so vague and inconsecutive that, as fer as 
possible, I shall endeavour to condease them in his own words : 
—*‘ Admitting that the conversion of the mechanical /orce into 
heat is sufficient to effect the melting part of the operation, there 
remains the greater difficulty of explaining the chemical and 
mineralogical features which characterise volcanic phenomena. 
For although mechanical force is admitted to be convertible into 
its equivalent heat, which in turn may ‘cause’ chemical action, still 
no such forces, alone or in combination, can transmute one 
