266 ' 
NATURE 
[Fed. 2, 1871 

custom in Domesday Book wien any place is an island, to call it 
so. For example, in vol. i, folio 75, ‘* Dorsete” [Dorset], we 
have—‘* The land of the King. 
which is called Porland [#.2. Portland]. King Edward held it in 
his life.” And again, same vol., fol. 396—‘‘ Hanteschire [7.e. 
Hampshire]. These lands below written lie in the isle of Wit” 
[Ze Wight]. 
In short, the Mount could not have been an island in 1086, 
because it then contained at least eight times as much land as 
it does at present, probably connecting it with the mainland, 
from which it is even now only one-third mile distant. The 
truth, Sir Henry Ellis says, seems to be that a hide, a yardland, 
aknight’s fee, &c., contained no certain number of acres, but 
varied in different places at different times. He sys there are 
«© four virgates in each hide, and thirty acres to make a virgate.” 
The elementary acre was 40 perches by 4 perches, as now. and, 
accordingly, the 8 carucates would amount to the respective 
numbers of acres mentioned in the last column of the following 
table at the respective times :— 
Periods Acres ina No. of Total 
Carucate Carucates Acres 
Carucate temp. Richard I. 60 8 480 
do. do. 100 8 S00 
do. Edward I. 180 8 1440 
do. 32 Edward III. (Oxon) 112 8 896 
do, Middleton 150 8 1200 
The hide is generally supposed to have been 120 acres. Now, 
taking the smallest of these measures, we shall have for the two 
hides 240 acres. The present area of the Mount, however, is only 
30 acres, so that there are 210 acres missing, How can we 
account for them except by supposing that the Mount extended 
further, perhaps in every direction? The hide of land taken by 
Earl Moriton was given to Mont S. Michel,* on the l’rench coast 
where Normandy joins Britanny, in 1085. 
I have before me ‘‘T'wo of the Saxon Chronicles parallel,” 
edited and commented on by the Rey, John Earle, formerly Pro- 
fessor of Anglo-Saxon, Oxford, from which the two following 
remarkable passages are extructed for the respective years 1014 
and 1099. 
“ y o14. And on this year, on Saint Michael’s-Mass-Even, came 
that great sea-flood through widely this land, and ran so far up 
as never before not did, and submerged many towns, and man- 
kind innumerable number,” p. 151. 
*t,099. This year also, on St. Martin-Mass-Day, sprang up 
that exceeding sea-flood, and so much to harm did, as no man 
not remembered that it ever afore did, and was that same day a 
new moon,” p. 235. 
. Nobody seems to contend that the coasts of Cornwall have 
simply been abraded ard cut back by the action of the sea during 
the Christian period. Nor does anyone appear to doubt that 
there has been a sudsidence. Now there are 210 acres of land 
missing since 1086, and in 1099, thirteen years a/éer, we have a 
record of a catastrophe which would fully account for the loss ! 
Supposing, whilst travelling in a foreign country, we were to 
come suddenly upon a city in ruins, when we had personally 
experienced shocks of earthquake a short time before. How 
could we doubt that the earthquake was the cause of the ruins, 
and how can we doubt that the remarkable event of 1099 caused 
the loss of land by subsidence and the Insulation of the Mount ? 
Sir Henry de la Beche (Report on Cornwall, &e., p. 417, et 
seg.) says “submarine forests are so common that it is difficult 
not to find traces of them in the district at the mouths of all the 
numerous valleys which open upon the sea, and are in any manner 
silted cups Winey It is well known that abundance of 
roots and stumps of trees have been found iv setu for some dis- 
tance on the south of the Mount. And no one seems to doubt 
that ‘the Mount was formerly five or six miles from the sea, and 
enclosed with a very thick wood,” and that: it was called in the 
Cornish language ‘the hoar rock in the wood.” 
Ihave before me the very interesting Prize Essay by Mr. John 
E. Thomas, F.G.S., written for the National Eisteddfod, held 
at Chester, 1866, upon the ‘‘ Encroachment of the Sea between 
the River Mersey and the Bristol Channel.’ + Prof. Ramsay, 
who had the adjudication of the prize, says, ‘t The result is so 
good, that I think this part of the Essay well worthy of the prize 
of 10/, anda medal.” Mr. Thomas does not look furtaer back 
than the year 520 for his sinkings in Cardigan Bay (p. 13), A 
* Penny Cyclop. Art. CorRNWALL. 
+ Published by Messrs, Spon, Charing Cross, price 14, 
‘The King holds the island | 
perusal of the whole tract of twenty-four pages will well repay 
gentlemen who take an interest in this particular department of 
geology. 
Jersey, Jan. 23 R. A. PEAcock 

Measurement of Mass 
Pror. EVERETT’S first letter contains the statement ‘* Descha- 
nel, in accordance with what has been till recent years an almost 
universal custom, employs a variable unit of force, and as de- 
pending upon this, a variable unit of mass, so that the number 
denoting the mass of one and the same body is diminished as the 
body is carried from the equator to the poles, and would increase 
up to infinity if the body fell to the centre of the earth.” 
I wished to point out that in making the standard pound a unit 
of force, by defining the place where it is to be used, we do not 
adopt a unit of mass which is variable, since if we take three 
times as much matter as gravitates with the unit force, we shall 
obtain the same mass at whatever point of the earth’s surface the 
gomparison is made. I cannot see that the adoption of this 
method necessitates any filing or loading of weights to suit change 
of latitude, since we invariably employ an ordinary balance and 
not a spring balance to effect our weighings. 
Whenever it does become necessary to compare gravitating 
forces, we are obliged to fall back upon the use of the pendulum, 
whether we adopt the old system of standards or the new. 
As a philosophical theory I am perfectly ready to admit that 
the standard pound is most appropriately considered asa standard 
of mass, but the employment of this standard in a text-hook for 
the use of beginners seems calculated to lead to confusion. 
If we refuse to commit ourselves to the absurdity of comparing 
the quantity of one kind of matter with the quantity of another 
kind of matter, I hardly see how mass is to be defined except 
by means of weight, and without, for the moment at least, em- 
ploying weights as measures of force, 
‘The assumption of a hypothetical force of gravity not de- 
pendent on latitude seems to stand on the same footing as the 
employment of a meax solar day; itis convenient, leads to no 
confusion, and is not unphilosophical. W. M. W. 

Mount Etna 
Ir may interest the observers who haye lately been in Sicily 
to hear that since their departure there has been a sad falling off 
in the appearance of Eta, The grand wreath of steam that 
used to 10ll out of the crater at such stately leisure that you 
could hardiy detect any movement without close attention, 
suddenly ceased about three days ago, aud left nothing more 
than a tiny wisp of smoke, rather suggestive of a cottage 
chimney than a volcano. 1 call it smoke because the colour 
became decidedly darker than it used to be, and the manner of 
its dissipation is different. Formerly, after issuing from the 
crater it used to assume true cloud forms, and lie about the 
mountain exactly like clouds: now, it diffuses itself as a thin 
veil over the sky ; sometimes being traceable in a streak as far 
as the coast of Calabria. Its volume is perhaps a thousandth 
part of what it was last week. It issues in a distinctly spiral 
form, the wreath oscillating apparently from side to side of the 
crater; and sometimes there are little puffs of extra size, whilst 
at others the wreath is nearly sundered. 
The date of the change cannot be very precisely given, although 
I have watched the mountain at all hours of the day for a week 
past, in hopes of getting a correct outline of it for pictorial 
purposes. The clouds only cleared off completely yesterday ; 
but I observed that a change in the wreath had taken place as 
early as Friday the 13th January. The weather up to the 15th 
has been outrageously squally and rainy, but is now superb. 
Last night there wasa magnificent display of zodiacal light, 
considerably brighter than we saw it at Augusta before the 
Eclipse, and distinctly traceable up to the zenith; the apex of 
the cone reaching to within about 10° of the Pleiades. It was 
brightest about 7 P.M., but was still visible at 10 P.M., when 
clouds shut it out. 
Taormina, Sicily, Jan. 17 Joun Brerr 
Note on Chromosphere Lines 
A VERY small but very bright prominence on the N. W. limb of 
the sun, observed at Xeres Dec. 21st, gave in addition to the 
| ordinary protuberance bright lines the following—one below C 

