or two points on which they seem to have misunderstood me. 
As one of the examiners who set the question challenged by Mr, 
Heath, I defended it, and pointed out that it bore a very close 
relation to medical science, besides showing, by the simplicity of 
the solution, that it was one of the mildest questions which could 
be set. 
If my friend Dr. Beale will refer to my former letter, he will 
see that I nowhere regard the production and waste of heat in 
the body as one of the mildest of questions. 
I ask whether a medical student should not know something 
of such important matters, and wish to imply that, in order to 
know, he must acquire some knowledge of the simplest prin- 
ciples of heat. He is not likely to acquire these unless 
they form a part of the preliminary training of medicai 
students. I presume Dr. Beale will admit that just so far as 
man can be regarded as a molecular body, capable of absorbing 
or radiating heat, to the same extent must the laws of molecules 
apply to him ; for his position is untenable that medical men 
need a knowledge of Physics, if the laws of Physics do not apply. 
His remarks on materialism are not warranted by anything in 
my letter, and do not apply tome. I will not attempt to answer 
in these pages the general questions proposed by Dr. Beale, on 
the heat-giving properties of food, or on the waste of heat from 
the body, nor to describe the methods by which researches on 
them have been or may be carried out, It is well known, anda 
medical man who wishes to be stamped with a medical degree 
ought to know, how much heat a given quantity of food is capa- 
ble of producing, and also that this amount of heat is exactly 
equivalent to a certain definite amount of energy: the form in 
which this energy will show itself in the human body in all the 
different stages of growth and decay, both in health and disease, 
is essentially a question for medical men to study, 
Physical Laboratory, King’s College W. G, ADAMS 
Diathermacy of Flame 
WILL you be so good as to allow me to draw the attention of 
your correspondent, Mr. W. Mattieu Williams, to what appears 
to be an oversight in his letter on ‘* The Diathermacy of Flame,” 
published in your number of Oct, 17 last. Near the bottom 
of col. 1, page 506, he says, ‘‘My flames were thus main- 
tained at a constant mean distance from the thermometer ;” 
and, farther on, ‘‘ Here, then, is a serlous discrepancy. I 
get an increase of 4° by the first addition of two flames, 
and by eight such additional pairs obtain an increase of 34° in- 
stead of the 32° due to theoretical diathermacy,” &c. The 
explanation of the discrepancy seems to be that the radiant heat 
from a flame, like that from any other body, varies as the inverse 
square of the distance, and therefore the total effect is propor- 
(Hoa ea eae ee es &c., not BS ee Meee os &e., 
ms a” a”, a'’ ad a’ ad 
where d, d", &c., are the distances of the flames from the 
thermometer ; in which latter case the order of lighting the jets 
would answer the desired object. 
Without going further into the subject, I would also draw 
attention to the desirability of keeping the gas at constant pres- 
sure, in order that the flames may be always of the same size and 
shape. It does not appear to be sufficient merely to record the 
quantity of gas consumed. 
The Castle, Parsonstown, Nov. 5 RossE 
The Corona Line 
Ir is rather absurd, as Capt. Herschel says, for an American 
to carry on a discussion with a resident of India through a London 
periodical ; but there are one or two points in his letter of July 
29th which I should like to notice. 
In the first place, let me acknowledge my mistake as to the 
original proposer of a chart of the spectrum based upon a scale of 
inverse wave-lengths ; the error arose in the manner Capt. H. 
supposes. Let me add also my profound satisfaction—shared, I 
am sure, by all who work with the microscope—on learning, a 
few months ago, that such a chart is in preparation, and that 
under the charge of a committee of the British Association. 
Next, as tothe question, ‘f What guarantee was there that 
No. 31 of the Preliminary Catalogue was the ‘coronal line,’ 
anterior to the Dodabetta measurements ?” 
In 1869 the case stood thus, so far at least as my own observa- 
tions are concerned:—In July I had found (not discovered, for 
3g 
(Woo. 14, 1872 
2 r 
Mr. Lockyer had anticipated me, although I did not kno 
until October) that the 1474 dark line was generally reversed 
the spectrum of the chromosphere. I had been led to exan 
this part of the spectrum with especial care by the report of gre 
lines seen by Pogson and Rayet during the eclipse of 1868. 
On the forenoon of the day of the eclipse of 1869 (Augu: 
this line was distinctly reversed at several points on the sun’s 
limb, and with my instrament nogother bright line could be seen 
near it. When, therefore, in the afternoon during the eclipse, I 
saw in that part of the spectrum a strong, solitary bright line, I 
considered myself warranted in identifying it with my old acquaint- 
ance, 1474, particularly as the measurements of Prof. Har 
with a one-prism instrument, accorded as well as coul 
expected, * 
In 1870 the matter was examined more critically. A 
minutes before totality, the 1474 line being already distinctly 
and even conspicuously, reversed, the cross wires of the spectro 
scope micrometer were carefully adjusted upon it, and as soon as 
totality began the corona all around the sun was thoroughly 
plored without disturbing the micrometer setting. The bright 
line remained entirely unchanged in position under the who 
dispersive power of thirteen prisms, very bright near the moon’s 
limb, but fading to imperceptibility at a distance of from 10 
to 20’. ‘ 
It seems to me, therefore, that the Dodabetta measurements 
must be regarded as merely confiming what was before full 
ascertained. Of course it was highly desirable that the fact 
should not be allowed to rest upon the testimony of any one 
observer. q 
Then as to another point—the puzzling coincidence between 
the coronal line and a line in the spectrum of iron. s 
The absence of hundieds of other and more important iron 
lines from the coronal spectrum, and the difficulty of supposing 
the vapour density of this metal less than that of hydrogen, 
of otherwise accounting for its presence in such quantities in the 
upper portions of the solar atmosphere, made it from the f 
highly improbable that this line could be due to iron. Now 
think I can add another fact pointing in the same direction 
During the past summer, observing at an altitude of more than 
8,oooft., I have repeatedly witnessed solar disturbances by 
which the b’s, the E lines, and the double iron line 1463 K 
(all in the same field with 1474) were considerably displaced and 
distorted, while 1474, and some other lines of unknown origin 
near it, were not in the least affected. I think therefore I may 
say that 1474 does not usually sympathise with the lines of the 
iron spectrum, and this adds to the probability that it is of 
different origin. ig 
But, on the other hand, so close is the coincidence, that the 
more I examine the matter, the harder it is to suppose that we 
have to do with a mere accidental juxtaposition. For one 1 am 
very anxious to hear whether the new and unequalled instruments 
of Dr. Huggins throw any further light upon the subject, and 1 
should be very glad to hear that they show the non-coincidence 
of the bright and dark 1474’s, because it would greatly simplify 
the problems, but I cannot say that I expect such news. e 
Now if the coincidence is absolute, there must be some reason 
for it ; either the coronal matter exists in terrestrial iron as an 
impurity, or the two substances have in their molecular consti- 
tution some similar dimension, some common parameter, which 
accounts for this identical vibration-period ; for I take it even an 
absolute coincidence between the lines of two spectra entirely 
independent in their origin is infinitely impossible—I mean of 
course coincidence determined to be such by a spectroscope of 
infinite dispersive power. ee 
As to the numerous coincidences observable upon the charts 
of Kirchhoff and Angstrém, between the lines of iron, titanium, 
and calcium, it seems most likely that they originate in the 
slight impurity of the metals used by the experimenters. Cer. 
tainly the matter merits most careful investigation, for if this is 
not the case a road would seem to be opened by which we may 
hope ultimately to penetrate many ot thesecrets of metallic 
molecules. C. A. YouNG 
Dartmouth College, U.S.A. Oct, 10 ‘ 
Ww 
- 
Brilliant Meteors 
ON Sunday evening, (Nov. 3), at 5.30, a magnifi 
‘*bolide” was observed at Glasgow, shooting athwart the sky. 
It made its first appearance in the Constellation Auriga (about 
