584 
NATURE 
[| JANUARY 22, I9QI4 
would have a principal line, A=694-5.10~°,, between 
the ultra-violet and the X-ray regions. 
But there is a serious difficulty. If N=20, n=4, 
where are the other 16 electrons required to make the 
atom neutral? Perhaps it is more reasonable to sup- 
pose that N for calcium is higher, and given by 
N-—Ss=19. In this case, N would not denote the 
place of the element in the periodic table, but would 
allow for intermediate and unstable forms of matter— 
an allowance which may well be necessary. The only 
alternative is to explain X-rays by the structure of the 
‘nucleus. Any internal ring must be one of doublets, 
such as neutral a particles. 
There is one other point to which I must refer. 
Mr. Moseley states that he has not found a corre- 
spondence between the X-ray spectra and the vibra- 
tions of the element nebulium treated in one of my 
papers. ‘This correspondence is not to be expected, for 
the two investigations are unrelated. The simple-ring 
atoms which I have used to interpret astrophysical 
spectra are supposed to have a simple nucleus, or to 
contain no a particles, and to be incapable of giving 
series spectra. They are not identical with ordinary 
atoms, into which, however, they appear to change 
in the stars which follow nebulz in order of evolution, 
and, as is shown in a paper in the Monthly Notices of 
the R.A.S. for December last, almost certainly by a 
modification of their nuclei. When this. change 
occurs, they show series spectra, which must depend 
on the nucleus, and perhaps on tubes of force, in a 
way which a mechanistic interpretation of Bohr’s 
theory may perhaps explain. In a paper read at 
the January meeting of the Royal Astronomical 
Society, these series were shown to lead to the same 
conclusion as Bohr’s with regard to the nature of a 
hydrogen atom. J. W. Nicroison. 
University of London, King’s College. 
Prof. Turner and Aristotle. 
Ix The Times report of December 29, 1913, of 
Prof. Turner’s lecture at the Royal Institution, his 
remarks on Aristotle are summarised in a way which 
will surely appeal to his sense of humour after his 
astonishment at my letter has abated. 
“ Aristotle said that a weight of to lb., for example, 
fell ten times as fast as a weight of 1 lb., and the world 
went on believing it for 2000 years. This raised the 
question whether it was better to believe things just 
because people told one, or to try to find out for 
oneself,” 
Aristotle never said this at all. Who | first 
fathered it on to him will perhaps never be known 
now, but since Galileo made the statement notorious 
323 years ago, the world has gone on believing it. 
If anyone wishes to find out for himself, let him 
consult the Teubner stereotyped Greek edition of 
Aristotle’s ‘‘ Physics,’’ Book IV., cap. viii., sect. 8-11, 
or the Leonine edition of St. Thomas Aquinas’s 
‘Opera Omnia,” tome ii., commentary on Aristotle's 
physics, texts 71 and 74, pp. 183-7. It is in the 
British Museum. 
Aristotle is discussing the notion of a vacuum, and 
using the argument from motion. Lection xi. in 
“Opera Omnia,” containing the argument, begins 
on p. 180, and is headed, *‘ Ex parte motus ostenditur 
non esse vacuum separatum."’ An intelligible para- 
phrase of the important parts of texts 71 and 74, or 
sect. 8 and 11, is as follows :—‘§8: We see that a 
heavy body is borne (or translated) faster for two 
reasons, either because of differences in the medium 
through which it passes, as earth or air or water, or 
other things being equal, because the body itself 
differs by reason of its superior gravity or buoyancy. 
NO. 2308, VOL. 92| 
As regards the medium, the reason is that it resists. 
... If air is twice as subtile as water, then for an 
equal distance the time of translation in water will 
be twice that in air. . . . §11:"As regards differences 
in the body itself. We see that those bodies which 
have greater potentialities of movement (pomjy, in- 
clinationem), whether downwards by reason of their 
weight, or upwards by their buoyancy, other things 
being equal as regards their shape (axa, figuris) 
are translated quicker over equal spaces, and this 
according to their proportionate magnitudes. But 
why should this be so in a vacuum? Therefore a— 
vacuum is impossible. But why is it that they have 
different rates of translation? In a plenum it is 
indeed of necessity, for that body which is the faster, 
is so by reason of its power or of its shape or of its 
potentiality of motion whether of translation or pro- 
jection, whereby it divides the medium more effec- 
tively. But in a vacuum all are equally effective, so 
that all are faster than one another. Which is im- 
possible.”’ § 11 is usually relied upon to convict Aris- 
totle of error, but it is evident that motion through 
a resisting medium is premised. 
The commentary of the Angelic Doctor makes this 
quite clear. The reader will find, probably to his 
amazement, that the new and modern notions of 
velocity were explicitly present to his intellect when 
he wrote. Special attention may be directed to § 13 
of the commentary on p. 187, beginning ** Deinde eum 
dixit, Secundum autem eorum.”’ He actually used 
the words, “vel propter aptitudinem figurae quia 
acutum est penetrabilius,” just as though he was 
describing the peculiar property of a modern pointed 
bullet. In the new and _ technical language of 
gunnery ‘“‘motus’’ or ‘“‘motus naturalis’’ is rendered 
precisely by the expression, ‘‘ terminal velocity,’’ the 
velocity at which the retardation of the medium, air, 
is exactly equal to the acceleration of gravity, result- 
ing in a constant speed of fall. That Aristotle ever 
supposed for an instant that a 2-lb. weight fell, in 
the ordinary sense of words, twice as fast as a 1-lb. 
weight is an absurdity. What he taught was that 
the terminal velocity of a heavy body, such as Prof. 
Turner’s sovereign, was greater than the terminal 
velocity of a light body, such as a feather, in a 
medium such as air or water. A penny can never 
fall faster than about 30 ft. a second through air. 
1 performed the experiment last week, dropping 
pennies from Clifton Bridge, 250 ft., into the Avon. 
They take eight or nine seconds to reach the water. 
Sir George Greenhill has often expressed doubts to 
me as to the correctness of the accusation against 
Aristotle’s common sense, but could never persuade a 
scholar to find the passage. A year and a half ago 
he showed me the above reference in the introduction 
of Mr. Lones’s new book on Aristotle’s ‘* Natural 
History,’’ and asked me to lools it up. I consulted St. 
Thomas’s Commentary in the British Museum, with 
the startling result I have mentioned, and fetched 
my former professor over to the reading-room to 
verify my discovery. That he did verify it must be 
my apology as a soldier for intruding into the domains 
usually preserved for scholars and philosophers of the 
highest order. 
. H. Harpcaste. 
27 Cranbrook Road, Bristol, January 9. 
TrEUBNER’S edition of Aristotle’s ‘* Physica” is out of 
print, but the equivalent passage is found in his 
Aristotle’s **De Coelo”’ (C. Prantl), p. 73, where the 
law is enunciated that the terminal velocity of a body 
in a medium is proportional to the weight. 
Aristotle’s law was justified by Newton in his ex- 
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