April 21, 1870] 
NATURE 
627 
accredited dictum of science as are the other doctrines of the 
correlation of the physical forces and of the correlation of the 
vital and physical forces which have been its necessary prede- 
cessors.”’ GILBERT W. CHILD 
Elmhurst, Great Missenden, Bucks, 
Prismatic Ice—Sandstone Boulder in Granite. 
THE ‘two phenomena” observed on Dartmoor by Mr. C. 
Spence Bate and Mr. W. Morrison, and described by the former 
in NATURE of the 31st ult., have been previously noticed. 
The late Rey. Dr. Scoresby, F.R.S., published a paper “ On 
Columnar Crystallisation of Ground Ice,” in the Zdindburgh 
New Philosophical Fournal for January 1850 (vol. xlviii.), and 
illustrated it with a plate containing eighteen figures. A pre- 
sentation copy of this paper is now before me. 
The so-called sandstone boulders in granite are by no means 
rare. They occur in various parts of Devon and Cornwall. I 
first noticed them at Shaptor, near Bovey Tracey, in Devonshire, 
and have subsequently seen them in several other localities, but 
nowhere in such abundance as at Sennen Cove, near the Land’s 
End, in Cornwall. There are several good specimens in my private 
collection. The following description of them occurs in a paper 
on ‘*The Age of the Dartmoor Granites,” which I read to the 
British Association at Manchester, and to the Royal Geological 
Society of Cornwall in 1861, as well as to the Devonshire 
Association in 1862. ‘‘ Nodules, apparently segregative, some- 
limes occurring in the substance of the ordinary granite, might, 
from the fineness of their grain, be almost mistaken for sand- 
stone ; indeed, I not long since heard them appealed to as 
proofs of the metamorphic origin of granite. ‘ Here,’ said ‘the 
appellant, ‘are unaltered remnants of the old sandstone rocks, 
which, with these exceptions, metamorphism has converted into 
granite. I do not quote this for the purpose of endorsing it, 
but simply to show the general dissimilarity of the nodules to 
granite proper. Excepting their darker colour, they reminded 
me much of the granite veins which pass through the older 
granite of Goatfell, in the Isle of Arran ; nevertheless, they are 
not veins but nodules, and capable of being extracted as such 
from the granitic mass containing them. .. . They consist of 
very fine grains of quartz and schorl in about equal quantities, 
or with the latter somewhat preponderating.”* 
Trrespective of the origin of the nodules, it is no doubt ‘clear 
that when this granite was formed, the temperature of (the 
surface of) the earth must have cooled down to below the 
boiling point of water,” for the granite, as has long been esta- 
blished, is of post-carboniferous age ; or, in other words, was 
formed after the rich faunas and floras of the Silurian, Devonian, 
and Carboniferous periods had successively passed away, to say 
nothing of the pre-Silurian organic eras. 
WM. PENGELLY 
Torquay, April 2 
The Transits of Venus in 1874 and 1882 
In the paper on this subject by P. L. S., there occurs a 
remark which is calculated to convey a mistaken impression. 
He states that ‘‘an Antarctic station is only required for the 
transit of 1882, and there is ample time to make a preparatory 
Antarctic expedition to ascertain” whether a suitable station can 
be found. The reverse is the case. No Antarctic expedition 
can be of any service in 1882, so that in a preparatory ex- 
pedition the lives of our seamen and men of science would 
be uselessly risked. On the contrary, there are several Antarctic 
stations suitable for observing the transit of 1874 ; and I have 
shown that the comparison of observations made at such stations 
with observations made in Siberia would give the most effective 
means of determining the sun’s distance available before the 
21st century. 
I may remark here, that the choice of stations for observing 
the transits of 1874 has been founded on calculations admittedly 
inexact, and it would be to the credit of English astronomy that 
the whole matter should be re-examined while there is yet time 
for a change to be made. In saying this, I am not by any means 
insisting upon the views put forward in my own papers on the 
subject ; though the only error pointed out by the Astronomer 
Royal in my charts and calculations consists in the fact that they 
aim at an unnecessary exactness. But the utilisation of the 
* See Geologist, 1863, p. 15; Trans. Roy. Geol. Soc. Com., vol. vii., p. 
425; or Trans. Dey. Assoc., 1862, p. 50. 
coming transits is a matter too important to be endangered for 
any personal considerations whatever. If errors have been made 
it behoves men of science to see that those errors shall not be 
suffered to prejudice the cause of scientific progress. 
RIcHARD A, PRocTOR 
Euclid as a Text-book 
I reGRET that Mr. Wormell has imported so much of a per- 
sonal nature into his reply to my former letter. Personality and 
unintentional misrepresentation appear to me to be its predomina- 
ting features. Unintentional, I say, for I know little of the writer 
beyond the fact of his being the author of two or more admirable 
text-books, and that he is a distinguished member of the London 
University. 
Though I feel that the columns of NATURE ought hardly to 
be taken up with such matter, yet, in self-defence, I am com- 
pelled to say a few words. As I have neither time nor inclina- 
tion for controversy, I hope that the discussion, if continued, 
will be entirely ad vem, and not diverge into personalities, Owing 
all my geometrical ability (gwod sentio quam sit exiguum) to a 
twenty-three years’ acquaintance with Euclid, and having had, as 
a teacher, to use that author for the last fourteen years, it would 
not be strange if I weve a favourer of the old system, which I am 
not to the extent Mr. Wormell seems to think, 
My plan of teaching geometry under the old system was to 
overcome Euclid’s deficiencies by viva voce explanation, and, 
offering slight assistance, to get my classes to work a number of 
geometrical exercises. With my sixth class I have generally 
got well through three or four hundred such exercises as are 
given in Todhunter’s edition of the Elements. 
This is not the same as sending out boys who have merely 
“committed Euclid to memory,” and certainly my pupils have 
found no great difficulty in the matriculation papers. Pupils 
thus prepared have taken first, second, third, and other high 
places in the examination, which places, I think, were in a 
measure due to their ‘flooring’ the geometrical papers—with 
the exception, perhaps, of a ‘‘rider ;” also, during the time I 
have held my present post, my pupils have carried off the 
Andrews Entrance Exhibition at University College each year, 
with one exception, when the finest geometer I have had was 
beaten. This is not the place for chronicling successes in other 
examinations. 
I did not state that it was advisable for students to read 
Euclid only ; what I did say was to the effect that I had heard 
of boys who were doing this with the idea that such a course 
would ‘‘pay” best. Mr. Wormell charges me with using an 
“‘infelicitous and ungenerous expression.” That I willingly 
retract, as it has struck myself as being uncalled for; but Mr. 
Wormell must have read my purposely concise letter hastily, 
for I nowhere say that I desire a change in the syllabus; the 
syllabus is excellent, and I quite agree with him in the remarks 
he adds about the ‘‘ unflinching courage in the reform of English 
methods of education” as far as regards the matter under 
discussion. But what is possible is, that the examiners, being 
chosen from the older universities, may overlook this distinction ; 
until now, I have had to regard the papers from the old point of 
view, in which light they have suited meexactly ; Mr. Wormell has 
viewed them from the modern stand-point, and bears the like testi- 
mony ; this being so, it must be admitted that the examiners 
have well carried out the syllabus. That I should ‘‘impeach the 
integrity” of such men as the present examiner, from whom I 
have always experienced the greatest kindness, or the late 
examiner, one of the most successful teachers of my own 
university, would be absurd, were it not that it pains me to have 
it supposed. To return, I do not want quite such a change as 
Mr. Wormell thinks ; the difficulty in my case has not yet 
arisen, for I have not yet sent in pupils whose training has been 
wholly confined to the new Geometry, and I wished to have the 
change made, if any were necessary, before sending them in. 
The difficulty will not beso great when we have obtained a 
thoroughly good modern text-book ; ours isa very good one, but 
there are blemishes which will doubtless be removed in a new 
edition, and to adapt it to the matriculation scheme more propo- 
sitions than at present must be proved, as I think, independent 
of proportion. I applied the term ‘‘ Euclidean type ” to the 
recent examination paper, because the questions are given in the 
exact words of Euclid ; I would have this changed; they follow in 
the order assigned inthe Elements, and perhaps my experience of 
