J FEBRUARY 24, 1923] 
NATURE 
255 

ear against the back of the violin and playing a scale 
on the pianoforte. Ellis (loc. cit. footnote) gives 
details of elaborate tests made by sounding tuning- 
forks over the { holes of a number of the best and 
oldest violins. There were at least two maxima in 
all cases, but the best specimens gave almost equal 
response to his forks from 240 to 560, and in the case 
of Dr. Huggins’s Stradivari of 1708, described as one 
of the best Stradivari, “‘every fork was more or less 
reinforced ; there was a subordinate maximum at 
252; a better at 260-268 vib.; very slight maxima 
at 312, 348, 384, 412, 420, 428 (the last of which was 
the best, but was only a fair reinforcement), 472-480, 
but 520 was decidedly the best and 540 good. No 
one fork was reinforced to the extent it would have 
been on a resonator properly tuned to it, but no one 
_note was Geletiornicd dl 
The peculiar shape of the body of a violin is such 
as to give double resonance even if the walls were 
rigid. Taking into account the vibrations of the 
wooden walls as well, we have a multiple resonator 
which will no doubt give an even response over a 
wide range in the best violin. 
Just as Sir Richard Paget’s double resonator 
modifies an artificial larynx to give vowel sounds, 
so the multiple resonator—the violin body—deter- 
mines the valued quality of tone of the violin. 
Multiple resonance gives promise of being a very 
fruitful field of research in acoustics. , 
P. ROTHWELL. 
Signals Experimental Establishment, 
Woolwich Common, S.E.18, 
January 15. 

Destruction of the Polarisation of Resonance 
Radiation by weak Magnetic Fields. 
THE earlier studies of the resonance radiation of 
mercury vapour in exhausted quartz tubes by one 
of the present writers showed no traces of polarisation, 
even when the exciting light was polarised. 
Recent experiments by Lord Rayleigh apparently 
indicated that polarisation existed in that part of 
the excited column at some little distance from the 
window at which the beam entered ; in other words, 
when the excitation was produced by light from 
which the core of the 2536 line had been removed 
‘by absorption. This observation was not verified 
in experiments made by one of us last spring and 
ublished in a recent number of the Philosophical 
agazine. The polarisation was found to be strong 
and of uniform percentage right up to the window 
at which the beam entered. 
On commencing a further study of the phenomenon 
we found it impossible to pe as strong polarisa- 
tion as was indicated by the earlier experiments, and 
after varying the conditions in every conceivable 
manner we finally found that the disturbing factor 
was the magnetic field of the earth, the polarisation 
rising to a very high value (90 per cent.) when the 
magnetic field of the earth was compensated by a 
large solenoid carrying a feeble current. In the 
absence of the solenoid the percentage of polarisation 
dropped to fifty or less. 
is appears to be a new magneto-optic effect, 
and is manifested only when the magnetic field is 
parallel to the magnetic vector of the exciting light 
and perpendicular to the beam of exciting rays. 
A field of only five or six times the strength of the 
earth’s field practically destroys the polarisation. 
Discrepancies found previous to the discovery of 
this effect were due to the fact that in some cases 
the apparatus faced north and south, and in others 
NO. 2782, VOL. 111] 


east and west. Lord Rayleigh’s observation was 
doubtless due to the stray field of the electro-magnet 
which was used to flatten the discharge against the 
wall of his quartz lamp. R. W. Woop, 
ALEXANDER ELLET. 
Baltimore, Jan. 25. 

Volcanic Activity in Iceland and Long Distance 
Transport of ‘‘ Dust.”’ 
Wirn reference to the communication on this 
subject made by Prof. Grenville Cole to Nature, 
November 11, 1922 (vol. 110, p. 635), the following 
additional remarks may be of interest. 
In the Deutsche Fisherei Zeitung for November 14, 
1922, occurs a note which may be summarised as 
follows: A Geestemunde steam trawler, the Tyr, 
while returning from her last trip to Iceland, experi- 
enced a fall of ashy material on her deck. This 
occurred while at a distance of at least 400 sea miles 
from Iceland. It is stated that the material was 
doubtless from Hecla, and though no date of the 
occurrence is given, it is known that the vessel made 
Geestemunde on October 25. A communication from 
the British Consul at Thorshavn also deals with this 
matter, and reads as follows : 
_ beg to inform you that on October 6 this 
sandstorm was observed on these islands. The 
weather was fine that day, but clouded, and the sky 
had a red-grey colour, and I remember the feeling 
of getting fine sand in my eyes while being in a rowing 
boat that morning, and going home to lunch my wife 
showed me some fine dark grey sand lying in the 
windows, which had been open that morning. 
“| may add that a telegram received from Iceland 
that day gave the news of volcanic eruption in 
Iceland.” 
For these two reports I am indebted to Mr. G. T. 
Atkinson, district inspector of fisheries, Eastern 
Area. J. N. CARRUTHERS. 
Ministry of Agriculture and Fisheries, 
Fisheries Laboratory, 
Lowestoft. 
The Wegener Hypothesis and the Origin of the 
Oceans. 
READERS of NatTuRE have been served with good 
reviews and discussions on the Wegener hypothesis, 
and it may therefore be of interest to point out that, 
so far as it relates to the origin of the Atlantic Ocean, 
this hypothesis was anticipated by previous writers, 
more especially byOsmond Fisher and W.H. Pickering. 
Fisher's views are well known to students of geo- 
dynamics, and Wegener himself refers to papers by 
W. H. Pickering and F. B. Taylor; but only by 
reading the accounts given by these authors can one 
realise how completely they forestalled Wegener, 
so far as the origin of the Atlantic by the westerly 
drift of the Americas is concerned. 
It was to accommodate Sir George Darwin’s views 
on the origin of the moon that Osmond Fisher 
suggested, first in NATURE (1882, vol. 25, p. 243) and 
afterwards in the second edition of his ‘‘ Physics 
of the Earth’s Crust,’’ that the Pacific Ocean is a 
scar and depression on the earth’s surface, left by 
the detachment of the moon. The following are 
Fisher's words (p. 380): “‘ The hole would be filled 
up by the influx of the molten substratum from 
beneath and around. The remaining crust would 
separate into larger and smaller fragments, and 
partly float towards the cavity. Thus when the 
