DECEMBER 17, 1896] 
NATURE 
153 
December 3, p. 100) seeks to justify his action on the ground 
that ‘‘ in a matter of such great importance . . . it is probably 
fair to conclude that, with the great majority of physicists, 
‘silence gave consent.’” This doctrine of silence is surely 
untenable. If an authority on acoustics pronounces views 
even on the fundamentals of sound, is an electrician to be held 
consenting when he forms no opinion or reserves it to 
himself ? In the present case it should be added that whilst 
questions in geo-physics or astro-physics are often most interest- 
ing to the public, they hardly as yet touch the fundamentals of 
physics, but constitute merely theoretical applications. If we 
put at 5 per cent. the proportion of physicists who have studied 
tor themselves any given problem in geo-physics, and who have 
the necessary qualifications to justify the expression of an opinion, 
we should probably indulge in an over-estimate. It is in fact 
only a very small minority of whom anything but silence could 
possibly have been expected. 
In the next place, even if the doctrine of silence were accepted, 
the occasion for applying it does not exist. A considerable 
number of persons—some in my opinion imperfectly equipped 
for the task—have criticised the theories of Lord Kelvin and Prof. 
Tait. _ In his letter Prof. Poulton represents all such critics as 
geologists or zoologists, but in his B.A. address (NATURE, 
September 24, p. 502) he admitted the existence of mathemat- 
ical critics. Most of these critics had, I think, in reality as much 
claim to the title physicist as to that of mathematician. I my- 
self five years ago, in two papers whose physical character was 
indicated by the title ‘‘ Some Applications of Physics and Mathe- 
matics to Geology,” while pointing cut that in my opinion the 
critics were mistaken in supposing they had demonstrated the 
essential erroneousness of Lord Kelvin’s work, advocated 
strongly the maintenance of an agnostic attitude towards the 
question of the solidity of the earth’s interior. These papers 
appeared in the Phzlosophical Magazine, were reprinted in the 
‘* Annual Report of the Smithsonian Institution,” and have been 
referred to since in several standard works. So far as I know, no 
attempt to controvert their arguments has been published, so 
that on the doctrine of silence they would seem to represent the 
views of the ‘‘ majority of physicists.” It is obvious to any 
mathematical physicist, and I should have hoped to others, that 
so long as the solidity of the earth’s interior is an open question, 
no theoretical application of the mathematical equations for 
solids—whether to temperature or any other internal property 
—can be regarded as final. 
My reason for advising Prof. Poulton to allow for possible 
errors in speculations other than Lord Kelvin’s, and for com- 
menting on the absence of any reference on his part to Lord 
Kelvin’s recent experiments on rock conductivity, was as 
follows :— 
The key-stone in Prof. Perry’s valuable contribution to the 
subject, on which Prof. Poulton so largely relies, is the 
demonstration that, even on the assumption of a solid earth, the 
hypothesis of thermal homogeneousness does not necessarily 
supply an absolute maximum to the habitable age of the earth, 
inasmuch as higher estimates can be obtained on the simple 
hypothesis that the internal strata conduct better than the 
surface strata. This disposes of the secessary character of Lord 
Kelvin’s conclusions on this subject—even if solidity be granted 
—but still may leave his estimate a not improbable one, so far 
as physical grounds are concerned, unless a presumption can be 
raised that the conditions of Prof. Perry’s problem exist in 
nature. A study of Prof. Poulton’s address led me to think that 
in his anxiety to increase the @ frzo77 probability of the conditions 
postulated in Prof. Perry’s solution, he was attaching undue 
weight to theoretical speculations which seemed to tell in its 
favour, while omitting all mention of recent direct experiments 
by Lord Kelvin which told against it. In my letter I quoted 
Prof. Poulton's own words, so far as space allowed, and 
certainly did not represent him as holding the theoretical evidence 
to be ‘*conclusive.” 
The second half of my first letter was intended to show Prof. 
Poulton, by reference to his own address, another aspect of the 
case, viz. the serious inroads which would be made on a 
physicist’s time if he criticised everything he thought erroneous. 
It seems that Prof. Poulton agrees mainly with my criticisms, only 
he maintains that the views criticised are products solely of my 
imagination. Flattering as it would be to my amour propre to 
believe my imagination so gifted, I must acknowledge the sus- 
picion that most physicists who read Prof. Poulton’s address, as 
published in Nature, will find a simpler explanation. Take 
NO. 1416, VOL. 55] 
for instance Prof. Poulton’s remark, ‘‘the earth, even when 
solid, will alter its form when exposed for a long time to the 
action of great forces,” and my criticism, “* here and in the rest 
of the passage is a strong flavour of the erroneous view that a 
solid is rzg7d@ in the mathematical sense, except when viscous 
under great and prolonged stress.” Elasticians, I suspect, will 
fail to recognise this as the criticism solely of an exuberant 
imagination. 
One word more: Prof, Poulton speaks as if the opinion of 
“the majority of physicists’’ were binding on their fellows. 
Now in the first place the voice of the majority is not yet 
recognised as dominant in science, and in the second place no 
provision exists for collecting suffrages. In the society of 
zoologists and geologists the individual physicist may possibly 
become a very fountain of universal knowledge, but amongst his 
peers he is chary about expressing too definite an opinion on 
questions he has not specially studied. CHARLES CHREE. 
December 7. 
The Satellite of Procyon. 
Tue announcement in the Astronomical Column of NATURE 
for November 19 (p. 62), of the discovery of a close companion. 
to Procyon by Prof. Schaeberle, with the 36-inch telescope of the 
Lick Observatory, will be extremely interesting to those who: 
know anything of the history of the investigations which have 
been madeas to the cause of the irregularity in the proper motion 
of Procyon observed by Bessel in 1844, and Madler in 1851. 
Following up their observations, Dr. Auwers in 1861 computed 
an orbit on the assumption of a circular motion In a plane per- 
pendicular to the line of sight, round a point about 1-2 distant, 
having a period of about 40 years, the position angle being 
about 90° for 1873, and this, with an assumed motion of about 
9° per annum, would make the present angle about 300° for the 
hypothetical companion. ieee 
Otto Struve measured a supposed new companion In 1873, 
March 28, with the 15-inch refractor at Pulkowa, and found, as 
a mean of several measures, the P. angle 90°"24, and distance 
12”°49; and also in 1874, April 10, when he measured the 
P. angle 99°°6, and distance 11-67; but, singular to relate, 
though looked for with the 26-inch telescope at Washington on. 
several occasions from November 1873 until January 1876, and 
also by the three Clarks (father and two sons) with the 
McCormick 26-inch telescope, Otto Struve’s: companion was 
missed by both instruments. ; 
The Washington observers, however, gave estimated places 
for three new companions within 10” distance ; but when Mr. 
S. W. Burnham, at the Lick Observatory, examined Procyon 
on the early morning of November 18, 1888, with a view to 
confirm all these observations or otherwise, he gave the follow- 
ing record :—“* Procyon.—Carefully examined with all powers up- 
to 3300 on the 36-inch under favourable conditions. Large star 
single, and no near companion.” : : 
Should the existence of the new companion, now said to be 
discovered by Prof. Schaeberle, be confirmed by other large 
instruments elsewhere, the orbit will likely prove to be an 
excentric one, and that the companion has just emerged fom 
the dazzling rays of the bright primary sufficient to allow it tobe 
measured with the 36-inch ; but after the previous Cee a 
the supposed discovery of other companions, astronomers wi 
be the more inclined to await further observations, especially as 
the new Yerkes 413-inch object-glass is now ready for mownae 
at the newly-erected Observatory, and will be in the hae ° 
such keen-eyed and experienced double-star observers as Messrs. 
Burnham and Barnard. 
In Nature for March 28, 1889 (p. 510); Mr. J. M. Barr, et 
St. Catharine’s, Ontario, suggested that photography might, oe 
employed to obtain the image of a satellite on the sensi aye 
plate by intercepting the image of the brilliant primary a 
suitable screen, and in Nature for April 11 following (p- 55 i 
in addition to other particulars, I referred to the nse 
difficulties connected with getting the impress of a pe eta 
faint companion, at the extremely close distance of eyonS three 
seconds of are. Isaac W. WARD. 
Belfast, November 30. 
The Leonid Meteor Shower. 
Ir the recent observations proved that comparatively few 
i yer ar x as 
meteors of this system were visible, they were interesting a 
i 1 “WITTE e ming 0 
showing the maximum to have occurred on the morning of 
