March 23, 1 882] 
NATURE 
’ Widget - Fish 4 ie . . 
481 
the public at all than that by the the use of the “vague but com- 
prehensible language of ordinary life,” such erroneous ideas 
should be propagated. I can assure Mr. Grant Allen, from no 
small experience of popular science-teaching, that the public 
mind is quite capable of drawing a very clear distinction between 
“living” and ‘‘extinct” animals, and would urge him to keep 
that distinction steadily in view in anything he may hereafter 
write on the subject. 
With reference to the sharks’ teeth brought up in the Challenger 
dredgings, in that part of the Pacific between Polynesia and South 
America, I may mention that only within the last week I have 
seen a collection of sharks’ teeth from a ‘‘ coprolite” digging 
in South America, among which was one of five inches by four, 
closely corresponding in its mineralised conditition with the large 
Challenger teeth ; and associated with them were rolled frag- 
ments of elephantine molars, presumably Jastedon Andium. 
And yet, according to Mr. Grant Allen, they belonged to our 
actual fauna ! W. B, CARPENTER 
56, Regent’s Park Road, London, N.W., March 20 
Fisher’s ‘‘ Earth’s Crust” 
THE verdict of NATURE on the Rey. O. Fisher’s ‘‘ Physics of 
the Earth’s Crust” is that ‘‘One or two points do seem to 
emerge from this assemblage of calculation as fairly clear and 
established on tolerably firm foundation. Such as that the con- 
traction of the earth by cooling is inadequate to the production 
of its greater inequalities.” .. That ‘there must be subter- 
ranean irregularities of density.” I ask for a fresh trial on the 
ground that the evidence is in-ufficient. 
On the first head, what Mr. Fisher has done is this. He has 
started with the assumption that no part of the earth became 
solid till the whole had cooled down to a uniform temperature 
of 7ooo° F. With this and some other minor assumptions he 
has been led to the conclusion stated above. And he has high 
authority on his side, for this is the assumption made by Sir W. 
Thomson in his well-knowr. paper, ‘‘ On the Secular Cooling of 
the Earth.” But the facts that an assumption is not in itself 
physically impossible, and that it enables you to integrate a tire- 
some differential equation and obtain numerical results, are not 
sufficient to establish the truth of the assumption. There are 
other ways in which the earth may have passed from a fluid to a 
solid state, some of them, to say the least, quite as probable as 
that which Sir W. Thomson adopts. I very much fear then 
that Mr. Fisher cannot be said to have established even his 
negative proposition. Indeed, to my mind, Mr. Fisher’s work 
seems rather to show that the earth did not consolidate in the 
way supposed by Sir W. Thomson. 
The second point, strongly insisted on not only by Mr. Fi-her 
but by many other eminent phy:icists, which the reviewer looks 
upon as finally settled, is the doctrine that the material of the 
crust must be denser beneath the ocean basins than beneath 
continents. The belief is grounded on the following argument. 
If this were not so, the preponderance of land on the northern 
hemisphere » ould attract the water, and the consequence would 
be that the sea-level would be higher in the northern than in 
the southern hemisphere. The answer is: Howdo we know 
that this is not so? At the outside the difference of level would 
not amount to more than a few hundred feet, and what is there 
to prove that the mean level of the sea in St. George’s Channel 
is not a few hundred feet farther from the earth’s centre than the 
mean level of the sea at the point diametrically opposite. It 
miyht be so, and we should none of us bea bit the wiser, The 
famous Indian deviation of the plumh-line, too, can hardly be 
looked upon as conclusive, when we reflect that it has been found 
capable of explanation in several ways by the ingenuity of the 
former Astronomer-Royal and the late Archdeacon Pratt. No 
problem that admits of several solutions can be appealed to as 
conclusive on a point like this. Mr. Fisher’s treatment of the 
Revelations of the Thermometer cannot either be accepted as 
satisfactory. Any one who has rough'y plotted to scale a 
section over the St. Gothard sees that a segment of a circular 
cylinder does net represent, even to a very loose degree of 
approximation, the contour of the mountain. 
The reviewer speaks of the cause to which Mr, Fisher would 
assign the contortion of the rocks of the earth’s crust as hardly 
adequate ; he might have safely gone further. That cause is the 
injection of lava into fissures, or, in other words, the formation 
of dykes. That contorted rocks are often traversed by countless 
dykes is a well-!nown fact. Take for ins'ance the dykes which 
seam so thickly the Paleozoic rocks of Scotland ; but here the 
dykes were formed long after the contortions, and besides their 
general direction does not coincide with the longer axes of the 
folds into which the rocks have been bent. In other cases of 
violently-contorted rocks there is a striking absence of dykes ; 
this is so along the coast of Glamorganshire and Pembrokeshire, 
where we have about the most marked case of intense folding 
and inversion in the British Isles. And this is still more strik- 
ingly the case in that marvellous example of contortion and 
inversion to bs seen in the Canton of Glaurus, which has been 
so graphically described by Heim. Nowhere, as far as we know, 
on the earth’s surface has inversion gone to the length it has 
here ; dykes do traverse the Paleozoic rocks, but they none of 
them run up into the Secondary and Tertiary beds, and the 
contortion did not begin till towards the end of the Eocene 
period. 
I for one should be only too relieved to think that some 
certainty, even if it were only of a negative kind, had been 
arrived at in the problems of the Physics of the Earth’s Crust, 
but I fear we are a long way off this happy consummation at 
present. A, H. GREEN 
Yorkshire College, Leeds, March 14 
An Equatorial Solar Spot 
THE occurrence of a spot close to the equator is so rare a 
phenomenon that it may interest some of your readers to know 
that there is such a spot now on the dice. 
On the 6th I noticed a spot, not long entered, and close to the 
equator ; it was a large, well-defined, regular, oval spot, with a 
mag. axis exactly parallel to the sun’s equator. On the toth, at 
toh. 45m. G. Astron. Time, this spot crosssed the prime 
meridian, at a distance from the centre of the disc equa} to 0°120 
the radius, measured towards the true north limb, in the direc- 
tion (156°-336°), ze. parallel to the sun’s axis. 
This distance, o'120 R., corresponds to hel. lat. 6°°9, mea- 
sured from the centre towards the north; therefore, as the 
latitude of the centre is now 7°:2 south, the true hel. lat. of the 
spot is 0°°3 S. 
The observations for determining the place of the spot were 
made on the roth at 4.45, and on the 11th at 12.45; during the 
interval the spot had crossed the prime meridian, and the 
‘ position” of the axis of the spot, which had remained con- 
staut from the 6th till 4.45 on the 1oth, had, during the interval, 
changed from (90°-270’), having reference to the sun’s axis, to 
(38°-218°), z.e. 52° in 20 hours. 
There was no further change from 12.45 to 4.45 on the 11th: 
and on the 12th the character of the spot was so altered that you 
could not distinguish any maj. axis at all. The instrument used 
was the 74-inch equatoreal refractor. WENTWORTH ERCK 
Sherrington, Bray, Co. Wicklow, March 13 
Seasonal Order in Colours of Flowers 
SIX years ago the question was brought forward in this journal 
(Vol. xiii. p. 427) whether light has any influence on the colour 
of flowers. I then called attention to the experiments made by 
Askenasy in 1875 (Botanische Zei/ung, 1876, No. 1), from which 
he inferred that the action of light was different, some flowers 
being changed by darkne-s, but others not. Having myself from 
time to time studied this subject, I have seen, like other observers, 
that several kinds of pigment appear in complete darkness, but 
that in many of these cases daylight strengthens the tint and in- 
creases the hue. Not only flowers, but also other j arts of the 
plant are thus affected. I found for instance that the shoots of 
several potatoes grown in the dark were coloured pink, that a 
bud of an elder-tree formed under the same circumstances two 
red-col.ured internodes, and that crocu-es, tulips, and hyacinths 
produced coloured flowers, wherea- ducuba japonica gave red- 
coloured fruits. It seems from these experiments that the plant 
is able to produce colouring maiter without help from any source 
of light. But it is an important fact that the colours formed in 
the dark and those fermed in the light often do not possess the 
same beauty. To prove this, I raised a bulb of | yacinth with 
two buds (or ‘‘ noses” as they are called by Dutch florists) ; cne 
of the two buds was covered by a piece of thick opaque paper 
to prevent the sun shining upon it, while the other bud was un- 
covered, and thus could enjoy the sun’s influence. After some 
weeks the difference was very marked, the covered flowers being: 
les intensively coloured than the others. This way of experi- 
