488 
NA TORE 
[Marcu 24, 1904 
with such an acute sense of touch as to discriminate an 
elongation of a micron, it would be superfluous to think 
out any arrangement which would serve to demonstrate 
the minute change of length due to magnetisation. Since 
the elongation generally amounts to a few millionths of the 
total length of the magnetised wire, it is necessary to have 
an intricate apparatus in order to show that the ferro- 
magnetic wire changes its length by magnetisation. The 
demonstration of magnetostriction to a large audience is 
thus a matter of no small difficulty. 
After trying in vain several means of showing the mag- 
netic change of length and the Wiedemann effect in a class- 
room, I finally succeeded in demonstrating 
them by using the capillary ripples formed 
on the surface of mercury. <A ferromag- 
netic wire AB is soldered at both ends to 
brass or copper wires AC and BD. D is 
bent into a hook, so that the wire can be 
properly loaded by hanging weights from 
it. Another wire DE is soldered at right 
angles to BD and bent downwards. The 
extremity of the wire carries a small plate 
P, and dips at the centre of a circular or 
rectangular mercury trough. AB is hung 
vertically in the axis of a magnetising 
coil, which should be much longer than the 
wire AB. By passing an alternate or 
intermittent current of known frequency 
fine capillary ripples are formed, which 
can be easily projected on the ceiling by 
placing a glass plate, inclined at 45° to 
the vertical, over the trough, and illumin- 
ating the trough by passing the sunbeam 
or electric light horizontally on the glass 
plate. By adjusting the weights, it can 
be easily demonstrated that for a current 
of given frequency the elongation or con- 
traction generally reaches a maximum. 
It may be doubted if the maximum is not 
due to the coincidence of the frequency 
with that due to the period of the elastic vibration of the 
wire ; repeated experiments show that this is by no means 
the case. 
Next place the magnetising coil horizontally, and stretch 
the wire horizontally by attaching to D a flexible string, 
which is slid over a pulley and pulled by the weights. The 
portion of the wire EP is bent downwards, and P dipped 
in a mercury trough. The other end, F, of the wire ED 
is dipped in a mercury pool, and an intermittent or alternate 
current of known frequency passed through the wire 
FDBAC. On magnetising the wire longitudinally by a 
steady current, fine capillary ripples are seen in the trough, 
which can be projected as before mentioned. 
As both effects are greater in nickel than in iron, better 
results are obtained with the former wire. 
H. NacGaoxa. 
Physical Laboratory, Imperial University, Tokyo, 
February 2. 
t 
Earth Structure. 
Krom Mr. Charles J. J. Fox’s letter in Nature of March 
10 it is not wonderful to learn that Prof. Milne emphasises 
the demand for some theory which shall explain pulsatory 
movements by which large tracts have been alternately 
raised and lowered. Prof. Milne has seen too much of 
seismic phenomena not to do so. But with our limited 
knowledge of the earth’s interior, it is still a matter of pure 
conjecture in what order the globe solidified from being a 
mass of heated vapours, and quite open to suppose that 
after the heaviest took the lowest place, a hollow was 
formed, and the crust became a cooling shell, with a layer 
of radium—about the heaviest of metals—underneath to re- 
main a perpetual generator of subterranean heat. This 
state of things may be taken as the starting point; for it 
was not until the crust hardened into shape that the problem 
for which Prof. Milne demands some effort at a solution 
came into existence, and if is curiously enough propounded 
by the picture which happens to be on the opposite page of 
NaturrE—* overfolding in Upper Carboniferous limestone ”’ 
—to account for which there are geologists who would re- 
NO. 1795. VOL 69] 
quire oscillations between land and sea continued for an 
indefinable length of time. 
It is easy to make a model range of strata in plastic 
clays and apply lateral pressure crunching them into 
similar foldings, while to stand before the real rock and 
coldly reason out what actual!y happened is another matter. 
Indeed, the present writer could make nothing that was 
not self-contradictory out of such contorted strata, especially 
when exposed on a very large scale, as occurs near Singa- 
pore, for instance, until on visiting one of the large (and 
active) craters in Java, a mile in diameter and with vertical 
faces 1000 feet high, the whole mystery at once became 
clear. For it was evident that a volcano (including fissures 
in the term) can erupt strata of every kind of material, red 
sandstone, conglomerates and shales, simulating those of 
aqueous deposition, and in all sorts of thicknesses from 
many feet to a few inches, the material being propelled for 
thousands of feet into the air, and perhaps all in the course 
of a few days of activity. Vesuvius, Etna, and even 
Hawaii can show nothing resembling the astounding 
volcanic formations in Java. 
The most capricious vertical and lateral movements are 
to be associated with volcanic action, but in the main it is 
successive deposition on uneven ground that manifestly 
causes the curvings which are to be so often noticed in ex- 
posed sections, and are typically delineated in the picture on 
p- 439. Adoption of this theory, drawn from what is to be 
seen round Java craters on a scale nowhere else matched, 
does no doubt introduce some modern views into established 
geology, particularly in the element of time and as to 
the origin of much of our coal. 
It is, however, widely allowed that there was a phase of 
great terrestrial instability just before the appearance of 
mammals, and equally certain that the vast ejections of 
successive periods varied in composition so as to give their 
special mineral character to the Silurian, Devonian, Carbon- 
iferous and later formations as classified by geologists. We 
can form only the faintest picture of the agitations on the 
surface of the globe in those days; of the tranquil intervals 
during which palms and forests grew, roamed in by 
animals, while shells were cast up on innumerable beaches ; 
and then of their sudden submergence under beds of volcanic 
ejections following in rapid succession, and reducing all 
life to fossils. Now that the earth has quieted down, the 
process is only faintly indicated by what has occurred in 
historic times, as, for instance, in the consternation pro- 
duced among the residents by the ejection of only a single 
covering of voleanic mud over many square miles of country 
at the eruption of Tarawera, in New Zealand, which the 
writer saw as a grey unctuous mass, evenly coating the 
surface of the landscape 18 inches thick six weeks after the 
eruption. Admission of the volcanic hypothesis, though it 
does not explain pulsatory movements on a continental area 
as yet, enables the origin of contorted strata met with so 
frequently in the British Islands and abroad to be recog- 
nised at a glance, as well as that of whole series of the 
stratified rocks. Al Tee 
London, March 15. 
Spawning of the Plaice. 
IN continuation of the letter you published last week 
(March 17), I can now supply some information as to 
spawning in the open sea. 
Mr. Andrew Scott, resident naturalist at the Piel 
(Lancashire) hatchery, who is now examining all our tow- 
nettings taken in the Irish Sea, reports to me that the first 
plaice eggs this year appear in a gathering taken by our 
fisheries steamer on February 2 at 13 miles south-west by 
south of Patches buoy, off Aberystwyth ; that the next occur- 
rence was on February 10, 6 miles west of Morecambe 
Bay lightship; and then again on February 18 at 6 miles 
north-west of the Liverpool north-west lightship. Plaice 
eggs have been present in every gathering since that date 
off both the Welsh and the Lancashire coasts. The Port 
Erin tow-nettings later than January have not yet been 
examined in detail. 
It is evident, then, that the plaice in the Irish Sea started 
spawning about a month earlier than those in our two 
hatcheries. It would be interesting to have the dates for 
the North Sea and the English Channel. 
Liverpool, March 22. W. A. HERDMAN. 
