Ig2 
NATURE 
[OcTOBER 2, 1913 
and discharges up to nearly half an ampere were 
obtained. Some of the published photographs are 
very remarkable. One of them showing the electric 
corona and streamers round the magnetised globe 
might easily be mistaken for a genuine photograph 
of a typical solar eclipse. Many of the phenomena 
of sunspots are also very strikingly imitated in the 
experiments. 
Birkeland proceeds to discuss the cause of the 
general magnetic field of the sun, the fact of the 
existence of which has been established by Hale. 
He attributes it to induced currents circulating in the 
interior of the rotating mass, which, he argues, can 
only have a comparatively feeble electric conductivity. 
He says (loc. cit. p. 540) :— 
‘‘We know that electric currents circulating in large 
globes formed of good electric conductors are of great 
persistence. Lamb found that for a globe of copper 
as large as the earth, ten million years would elapse 
before the currents fell to 1/¢ of their former intensity. 
The induction effects produced by electric rays 
emanating from sunspots may therefore give rise to 
currents of long duration if circumstances permit. It 
is probable that as regards the sun, we shall be 
obliged to suppose a somewhat feeble conductivity of 
the gaseous interior, to the intent that the electric 
currents created and circulating within it are reduced 
with a fairly high rapidity and are transformed into 
heat.”’ 
In a recent communication to the Royal Astro- 
nomical Society,” the writer brought forward some 
evidence deduced from laboratory experiments, which 
led to a contrary conclusion, namely, that the gaseous 
matter composing the sun must be a highly conduct- 
ing medium. The experiments of Kaye* and the 
writer showed that carbon and a number of metals 
emit on heating ionisation currents of a relatively 
very high order of magnitude, and this in absence 
of any external applied potential and at atmospheric 
pressure. The currents are almost certainly carried 
by swarms of negatively charged particles of relatively 
considerable mass, the emissivity of the emitting sur- 
face increasing very rapidly with increase of tem- 
perature. 
In the interior of a carbon-tube resistance-furnace 
heated by alternating current, tne apparent gaseous 
resistance of the order of megohms at 1400° C. fell at 
the highest attainable temperature to a small fraction 
of an ohm, due to the emission from carbon alone. 
In one series of experiments where temperature 
measurements were made, the conductivity increased 
exponentially nearly two hundred-fold for each rise of 
tooo° C. Impurities such as iron and silicon, which 
are generally present in ordinary samples of carbon, 
may further increase the conductivity four or five fold 
during the first heating of a new furnace. Though 
influenced somewhat by the surrounding gas, the 
emissivity appears to be invariably present in neutral 
or reducing media. The experiments of King, briefly 
referred to by Hale in his paper in the current 
number of The Astrophysical Journal, show that 
though the emissivity of carbon falls with increase of 
pressure, it is still apparent at 20 atmospheres. 
Seeing that the temperature of the sun is probably 
between 5600° and 6000° abs. and that of those 
elements shown to possess an appreciable electric 
emissivity, carbon, and iron at any rate are present 
in the solar atmosphere in considerable quantity, it is 
difficult to avoid the conclusion that the degree of 
ionisation, and consequently of electric conductivity, 
® Harker, ‘On the Origin of Solar Electricity.” 
the Royal Astron, Soc., June, 1913. 
% Harker and. Kaye ‘‘On the Emission of Electricity from Carbon at high 
Temperatures." Proc. Roy. Soc. A. vol. Ixxxvi, 1912, pp. 379 to 396. 
“On the Electric Emissivity and Disintegration of Hot Metals.” Proc. 
Roy. Soc. A. vol. Ixxxviii, 1912, pp. 522 to 538. 
NO. 2292, VOL. 92] 
Monthly Notices of 
must be very high; probably at least as good as that 
of the globe of copper considered in Lamb’s computa- 
tion. 
The bearing of these conclusiens on Birkeland’s solar 
theory seemed worthy of some consideration. 
J. A. Harker. © 
Teddington, September 16. ; 
A New Aquatic Annelid. 
Asout the middle of September I received from Dr. 
H. F. Parsons, of Croydon, a fresh-water Annelid 
which had been found in the water supply of Ring- 
wood, Hants, and sent to the Local Government Board 
for identification. It proved to be an immature but 
very beautiful specimen of Rhynchelmis limosella, 
Hoffm., a member of the Lumbriculide. It is of 
peculiar interest, inasmuch as it confirms a suspicion 
expressed by Beddard in 1895. He remarks (‘‘ Mono- 
graph of the Order Oligochzta,” p. 215) that “the 
genus Rhynchelmis is, so far as our present know- 
ledge goes, confined to the fresh waters of Europe. 
...I1 have seen a specimen from some part of 
England, but cannot give any details. I believe this 
specimen to be in the Oxford Museum. There is 
every probability that it is a native of this country.” 
I have collected annelids in almost every part of the 
British Isles, but hitherto have never had the good 
fortune to come across the species here named. It is, 
therefore, very gratifying to be able to record it as 
a new addition to our Annelid fauna. 
HILpERIc FRIEND. 
Pocklington, York, September 20. 
MODERN ELECTROMETERS. 
ECENT research on the electron and radio- 
activity has necessitated so many refined 
electrostatic measurements that much attention 
has been directed to the design of electrometers, 
and several different instruments distinguished by 
their sensitiveness and convenience in working 
have been devised. Two types have served as 
the starting-points for modern improvements, the 
first being the gold-leaf electroscope, and the 
second the quadrant electrometer of Lord Kelvin; 
great progress has been made by bettering the 
insulation, the sensitiveness, and the accuracy and 
ease of observation, and further by important 
modifications of design. Polished amber or 
ambroid, a substance made from compressed frag- 
ments of amber, is now generally used as insula- 
ting substance, and for the first type of instru- 
ment the deflection is now measured with a read- 
ing microscope; for the second the mirror and 
scale is employed. 
The gold-leaf instrument is used in many forms. 
In a modification by Exner a leaf is fastened on 
either side of a narrow, vertical, insulated metal 
plate, while opposite each leaf is a metal plate 
the distance of which from the central plate can 
be adjusted, thus controlling the sensitiveness ; 
for potentials of some hundred volts this is a con- 
venient form. For higher potentials of thousands 
of volts Braun’s pattern, with a light rigid needle 
pivoted a short distance above its centre of mass, 
is much used. For very sensitive measurements 
C.T.R. Wilson has recently modified the gold-leaf 
electroscope in his so-called “tilted electrometer.” 
In this instrument a single hanging gold leaf is 
attracted out of the vertical by an inclined insu- 
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