' 
; 
FEBRUARY 12, 1914] ) 
suppose that Prof, Pearson would actually accuse 
Major Darwin and myself of such dishonesty, but he 
has not guarded his words against the possibility of 
this interpretation being put on them, and so I meet 
the charge—in the only way possible—by a flat 
denial. 
‘It is interesting to inquire how the mistake under 
discussion could have arisen, It seems probable that 
the words ‘‘last few months’’ conveyed. the idea of 
some indeterminate period of time, and that this idea 
and not the actual words were held in the memory, 
afterwards to be retranslated into words as ‘‘last 
years.” This would probably not have occurred if 
Prof. Pearson had himself been a little more precise 
in the first instance. The interview which he refers 
to during which Sir Francis Galton expressed doubts 
concerning the policy of the Eugenics Education 
Society took place about three weeks before Galton’s 
death. Is three weeks the precise period which Prof. 
Pearson describes as a few months? The last letter 
quoted in The Eugenics Review in answer to Prof. 
Pearson’s original letter was written, not in 1909, but 
in October, 1910, about three months before Galton’s 
death. 
Finally, when Prof. Pearson wrote,- ‘tI have no 
other effective means except through the courtesy of 
your columns to correct a wholly erroneous statement, 
which the editor of that society’s journal has put into 
my mouth,” had not he already received a letter from 
Major Darwin apologising for the mistake, and assur- 
ing him that it would be corrected in the next number 
of The Eugenics Review? 
EpGar SCHUSTER. 
110 Banbury Road, Oxford, January 30. 
Origin of Argentine Wild Horses. 
ANENT the recent discussion as to the origin of the 
wild (or feral) horses of the Argentine Republic, there 
is one line of evidence to which I venture to direct 
attention. That is the question of infertility. 
Assuming, as I suppose most reasonable people do, 
that the South American horses were derived origin- 
ally from the north—whether in the northern part of 
North America or in north-eastern Asia is immaterial 
—and that the South African horses are similarly 
derived, it would seem that the Argentine species 
would be at least as remote geographically from the 
wild ancestors of the domestic horse as are the modern 
zebras and asses, and could not be any more nearly re- 
lated genetically. The species native to the Argentine, if 
they continued to exist down to modern times, would 
have evolved in complete isolation from any northern 
species since the early Pleistocene at least, and prob- 
ably longer as regards any Old World species. Now 
the infertility of crosses between zebras or asses and 
domestic horses is based upon a separation that does 
not appear to date earlier than the late Pliocene. 
Beyond that they must be derived from a common 
stock. The autochthonic Argentine horses were there- 
fore not any more nearly related to Equus caballus 
than are the zebra or the ass. They should therefore 
be equally infertile when crossed with the domestic 
stock. (The degree of infertility of distinct species 
varies in different families of mammals; but the 
known facts regarding the horse, asses, and zebras 
afford a measure of its degree in this family.) So 
far as I know there is no record of infertility in such 
crosses, and since, as I am informed, the wild horses 
are caught and domesticated on the pampas just as 
they were in the western United States, any such 
infertility could scarcely escape notice. This would 
seem to me to be a decisive argument against the 
theory that the existing wild horses of South America 
NO. 2311, VOL. 92] 
NATURE 
661 
are descended either wholly or partly from any sur- 
viving native stocks. The argument would apply 
with less force to the wild horses of the western 
United States and- Mexico, yet even with these it 
would appear to be a strong point. But the geologic 
evidence against the survival to modern times of any 
native horses in North America is very nearly conclu- 
sive in itself. 
Even if we admit that some of the native horses 
may have survived in the Argentine until the time of 
the Spanish settlement—and I think that the evidence 
for that contention is strong, and that it is quite in 
conformity with some other features in the faunal 
history of South America—the native stock would pre- 
sumably be no more able to interbreed with domes- 
ticated or feral stock of Equus caballus than could the 
quagga in South Africa. It would remain separate 
and immiscible until exterminated. No strain of it 
could survive in the modern feral horses. 
W. D. MattHew. 
American Museum of Natural History, 
New York, January 15. 
Specific Heats and the Periodic Law. 
At his last Friday evening lecture at the Royal In- 
stitution Sir James Dewar announced his somewhat 
startling discovery that at temperatures of about 20° 
absolute the specific heats of the elements are periodic 
functions of the atomic weights, and are therefore not 
in accordance with Dulong and Petit’s law (estab- 
lished at ordinary and higher temperatures). May I 
venture to point out that a simple consideration of the 
difference of conditions in the experiments of Sir 
James from those of Dulong and Petit may ultimately 
harmonise the two sets of results? 
From Guldberg and Wage’s ‘mass law” it follows 
that the velocity increases with the mass (atomic 
weight), but this increase of velocity takes place at 
higher temperatures at a very much greater rate, with 
the result that at higher temperatures the atomic mass 
becomes relatively less important, i.e, the special atomic 
properties will be less emphasised. The velocity factor 
becoming so predominant, a proportionately ‘smaller 
additional increase of (heat) energy will be required to 
raise the mass to a higher temperature, 1.e. the specific 
heat will be inversely proportional to the mass (Dulong 
and Petit’s law). At very low temperatures—say at 
about 20° absolute—when the velocity is very smal]— 
almost negligible—the mass of the atom is the pre- 
dominant factor, and hence we find a periodic function 
of the atomic weight as the expression of the specific 
heat as well as of the other (physical and chemical) 
properties. The above suggestion might be tested by 
experiments to find a temperature at which neither 
the Dulong and Petit nor the Dewar law would be 
strictly obeyed. H. Lewkowirscu. 
22 Meadway, Hampstead Garden Suburb, N.W., 
January 31. - 
The End-product of Thorium. 
In continuation of our letter published in Nature 
of February 5, containing a suggestion as to the 
nature of the end-product of thorium, we would point 
out that, of course, our view involves atomic weights 
for the various disintegration products of thorium 
higher than is ordinarily assigned to them, and that 
therefore the determination of the atomic weight of 
any one of them would afford atest of the truth of 
the hypothesis. Jory. 
J. R. Correr. 
Iveagh Geological Laboratory, Trinity College, 
Dublin, February 7. 
