606 
NATURE 
[Aucusr 15, 1912 
ence on the Babylonian versions. He then turns 
to Africa and shows how not only the ancient 
Egyptians but also various modern races in that 
continent possess traditions of a similar charac- 
ter. In subsequent sections he continues his 
survey of beliefs for which evidence has been 
forthcoming in Australia, Melanesia and Polynesia, 
the Malay States, the peoples of Central and East 
Asia, North and South America, and the Indo- 
Germanic races. And he points out the remark- 
able recurrence of the story or myth of a sudden 
and destructive deluge. This nearly universal 
tradition he would not explain as a single original 
legend which has spread over the whole world, 
any more than he would trace it to an actual flood 
or deluge. The explanation he puts forward is 
that the deluge story in its numerous variations 
is a mythological presentment of celestial pheno- 
mena, reflecting the clouding over of the bright 
heavens by heavy rain-clouds, the differing details 
of the various forms of the legend being projected 
in accordance with the universal laws of anthropo- 
morphic symbolism. It is the fashion at present 
in Germany to explain most mythologies by an 
astral system of interpretation, and Prof. Gerland’s 
conclusions will be welcomed by adherents of the 
astral school. The weakness of all such theories 
is that the astrological myth is a product, not 
of primitive races, but of peoples that have at- 
tained a comparatively cultured and reflective 
stage of thought; and to explain a primitive myth 
by astrological theory is really to put the cart 
before the horse. But Prof. Gerland states his 
case in a remarkably able and persuasive manner, 
and the book embodies a valuable survey over an 
extremely wide range of study. MS Wie VS 
TED AREL RSS) eli Ommele Ean) Di Oe 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications.] 
The Effects of Friction in a Vacuum on Thorium Oxide. 
For two years past I have been experimenting on the 
action of sand, powdered beryl, and other substances 
within vacuum tubes of soft, fairly conducting soda 
glass, and I have obtained interesting results respect- 
ing the outflow of electrons when the tubes are insu- 
lated by sulphur blocks and worked on a rocker. 
The electrodes and a belt of tinfoil on the outside are 
connected by thin wires to three electroscopes with 
graduated scales, and the potentials at various stages 
of the experiments are found to fall gradually, in the 
case of sand, from a height symbolised by readings 
of 60° or more down to zero after some thousands 
of rockings, and this without any visible effect on 
the glass. The electrons are swept away and the 
tubes become absolutely dead. The passage of a 
current from an induction coil through them 
accelerates the sweeping process, and rest, even for a 
year, does not revive their action. 
The case is essentially different from that of mer- 
cury in quartz. The nature of the glass renders each 
tube a form of closed conductor. It contains no insu- 
lated charge, but develops electricity within. itself, 
shows flashes in the dark, and maintains an outflow 
for many hours. 
NO. 2233, VOL. 89] 
Recently, however, 1 have tried the substitution of 
pitchblende, thorium oxide, black oxide of uranium, 
and other metallic oxides for sand, testing signs, re- 
cording results, and earthing the electroscopes at the 
end of each ioo reversals. 
As the total amount of activity is a principal point, 
I have added together, for the purposes of the curves, 
the readings of the two electrodes irrespective of sign; 
but I deal with signs in noting the behaviour of the 
substances. As control experiments, I made fresh 
tubes (like the others, 47 cm. long and 12 cm. 
internal diameter) containing barium peroxide and 
manganese dioxide. The former, after momentary 
action, ceased to show any effect whatever; the latter, 
acting very much like sand, reached a maximum of 
40° (one electrode giving +28°, the other —12°), and 
then, falling away rather sharply, became absolutely 
dead after 5200 reversals. The uranium oxide (U,O,) 
acted very feebly, only reaching a maximum of +7°; 
but it continued during 3000 reversals to indicate that 
the inside of the tube was positively charged. 
The thorium behaved very remarkably. Rising 
during the first 100 rockings only to +10°, the read- 
ings grew gradually higher. During the first 2500 
reversals one electrode had shown a minute negative 
charge, the other a fast-growing positive charge; but 
at that point the whole interior became positive, and 
so remained, the readings going up to +40°. The 
So 
60 : 
4o 
+ E i 
» 
F HHT 
0 + + rt 
MEET Cer ah Te 
Teversals 
curve, drawn from readings taken on cessation of 
rocking, does not convey a due impression of the 
vigour of the action, or of its promise to continue 
unabated for an indefinite time; but we see in it a 
rise from inertness to strong electrification, and while 
we must, perhaps, look for a substratum of glass 
action, we know from sand and manganese and from 
barium peroxide that this either weakens and ceases 
altogether or does not occur at all. The thorium 
oxide is, of course, far from being a simple combina- 
tion of thorium and oxygen. Radio-thorium, thorium 
X, and an emanation would alone complicate its 
action, and the constant movement in the tube would 
diminish the suppression of the positively charged a 
particles by the upper layers of the oxide, but the total 
of these effects is small. The sum of the radio-active 
powers of the thorium when at rest is so very limited 
that it is hard for one who has witnessed its vigorous 
action in a tube, and the strong positive charge 
developed, to keep from believing that friction in a 
vacuum has done that which no chemical process can 
effect. 
This impression of a mechanically-produced increase 
of radio-activity was much strengthened by the be- 
haviour of pitchblende in very fine powder. From the 
first moment the action was vigorous, and after a few 
hundred rockings the whole interior of the tube be- 
came negative and so remained. The readings rose 
quickly to a level much above the thorium figures, 
and then, after about 4000 reversals, made a_ yet 
greater upward start, which was maintained with an 
