640 

—lies the generative organ, an hermaphrodite gland. 
We remove the whole of this part of the body and 
leave the front part to regenerate and to reproduce 
a new generative organ; that is, mew germ plasm is 
formed from somatic tissue. It has been established 
already in sev eral species of animals and plants that 
Weismann’s “continuity of germ plasm” is not 
obligatory but, at most, a facultative continuity. The 
long-siphon Ascidians with regenerated germ plasm 
give birth to progeny also long-siphoned. In this 
way the most familiar objection brought against the 
inheritance of acquired characters—the claim that 
there is a direct influence on the germ plasm—is, I 
think, definitely removed. The local character of the 
operation in cutting off the siphons renders this chief 
objection almost inapplicable. We might, however, 
still argue that physical influence still obtains ; that 
while I am cutting the siphons at the head, a direct 
physical reaction is taking place on the germ plasm. 
In this case there would already be established that 
tendency which would give rise to an apparent in- 
heritance in the progeny. 
But now we cut away all the generative organ, with 
all its germ cells and its active and latent tendencies. 
The Earth’s Electric and Magnetic Fields.t 
By Prof. W. F. G. Swann, University of Minnesota. 
i 
UITE apart from those more spectacular mani- 
J festations of atmospheric electric phenomena 
associated with the thunderstorm, we have to recognise 
the following facts, as pertaining to the ordinary quiet 
day : 
(x) The earth is charged negatively to such an 
extent as to give rise to a vertical potential gradient 
which amounts to about 150 volts per metre at the 
surface of the earth, and goes through fairly regular 
variations throughout the day and throughout the 
year, variations amounting to 50 per cent. or more of 
its total value. 
(2) The potential gradient diminishes with altitude 
until its value at ro kilometres is practically negligible 
compared with that at the earth’s surface, a result 
which is brought about by the existence, in the atmo- 
sphere, of a positive charge, the total amount of which 
below the altitude ro kilometres is practically equal to 
the negative charge on the earth’s surface. 
(3) The atmosphere is a conductor of electricity. 
The conductivity near the earth’s surface is so small 
that a column of the air one inch long offers as much 
resistance to the flow of the electric current as would a 
copper cable of equal cross section extending to the 
star Arcturus and back twenty times over. 
(4) In spite of the smallness of the conductivity of 
the atmosphere at the earth’s surface, its amount is 
nevertheless sufficient to ensure that go per cent. of the 
earth’s charge would disappear in ten minutes if there 
were no means of replenishing the loss. 
(5) The conductivity increases with altitude at such 
a rate that its value at an altitude of 10 kilometres is 
* Portions of a lecture on “ Unsolved Problems of Cosmical Physics,” 
delivered before the Franklin Institute on December 20, and published in full 
in the Journal of the Franklin Institute. 
NO. 2793, VOL. 111 | 
NATURE 


[May 12, 1923 
We await the growth of a new generative organ. 
The regeneration takes place at a time when there 
are no further disturbances influencing the body. 
Nevertheless, the growth to which it gives rise is still 
affected. The change thereforg cannot have been 
lying preformed in the original germ plasm. It can 
have come ultimately from nowhere but from the 
changed body. 
The present circumstances are scarcely | favourable 
for the furtherance of these researches in heredity 
in my impoverished country. During the War experi- 
mental animals, the pedigrees of which were known 
and had been followed for the previous fifteen years, 
were lost. I am no longer young enough to repeat 
for another fifteen years or more the experiments, 
with the results of which I have been long familiar, 
before I attempt to break new ground. The neces- 
sities of life have almost compelled me to abandon all 
hope of pursuing ever again my proper work—the 
work of experimental research. I hope and wish with 
all my heart that this hospitable land may offer oppor- 
tunity to many workers to test what has already been 
achieved and to bring to a satisfactory conclusion what 
has been begun. 
' 
about fifty times that at the earth’s surface, and there 
is indirect evidence to substantiate the belief that at 
altitudes of the order of roo kilometres it may attaina 
value more than ro times that at the earth’s surface. 
Such a conductivity would cause the upper atmo- 
sphere to act, practically, as a perfect conductor in 
its relation to phenomena in the lower atmosphere. _ 
(6) There is some evidence for and some against the 
view that our atmosphere is traversed by a radiation 
of cosmical origin, and of penetrating power ten times, 
or more, that of the gamma rays of radium. 
A potent factor contributing to the conductivity of 
the atmosphere is the radioactive material in the air 
and soil. There are, on the average, about 1.5 mole- 
cules of radium emanation per c.c. of the atmosphere | 
over land, yet this small amount is sufficient to contri- — 
bute very appreciably to the ionisation there. On the — 
basis of the known amounts of radium and thorium — 
emanations in the atmosphere, and of radioactive — 
materials in the soil, we could account fairly well for 
the ionisation of the lower atmosphere. The con-— 
ductivity of the air over the great oceans is, however. 
practically as great as it is over land, and is very much 
greater than can be accounted for by the radioactive R 
materials, which are negligible in amount in the 
and in the air over it. The assumption of a penetrating 
radiation would provide a cause for the ee } 

known to exist over the sea. If, however, we are un: 
willing to admit the existence of such a radiation, th 
ionisation over the ocean remains to some extent ¢ : 
mystery, and may have to be attributed to a smal 3 
spontaneous ionisation of the gas. s 
The great problem of atmospheric electricity is, of © 
course, “the explanation of the maintenance of the — 
earth’s charge. The replenishment to be accounted — 
for is small, amounting to only 1000 amperes for the — 
