288 

demurs, respecting the willingness in Cambridge to award fellow- 
ships for merit in Natural Science, by making inquiries of the 
tutors of the several colleges. This I trust he will do, and if he 
takes the opportunity of impressing upon them the advantage of 
following the example set by Trinity of absolutely offering a 
fellowship or fellowships as the reward of great proficiency in 
Natural Science, he will be doing a great service, for that is un- 
questionably an important desideratum. At the same time, I 
would ask him to take the trouble to ascertain whether there 
have recently been in Cambridge any persons of great proficiency 
in Natural Science to whom fellowships have not been awarded. | 
A close and fair examination of the matter will, if I mistake 
not, prove to him that the colleges have not been backward in 
this way in rewarding real merit in Natural Science; that 
there is in some colleges not only a willingness but an anxiety 
to do this; and that the arena is opening for Natural 
Science to enter the lists against Classics and Mathematics, 
with the prospect of a fair adjudication of fellowship prizes. 
**M.A.” will do a further great service if he can turn his 
wide acquaintance with the members of various colleges to 
account by inducing the colleges to offer more Scholarships for 
proficiency in Natural Science, instead of limiting them so much, 
as is at present done, to students who have not commenced a 
University career. The stimulus thus afforded to the study of 
Natural Science by undergraduates would have the effect of pro- 
ducing a greater number of candidates deserving fellowships, and 
the more frequent award of fellowships to them. 
THE WRITER 
Feb. 4 OF THE ARTICLE IN QUESTION 
Prismatic Structure in Ice 
DuRINc the late frost and subsequent thaw, I have watched 
the ice as far as was in my power to see whether its demeanour 
bore out Mr. Langton’s explanation of the prismatic structure 
(NATURE, vol. iii. p. 105) in reply to my communication (Id. 
voli. p. 481). At the time when I received his letter, I felt 
unable to accept the compromise which he proposed, and the 
result of these last investigations has been to confirm my previous 
opinion, Let me, however, first explain away a slight miscon- 
ception into which I have led him. In using the words ‘‘ severe 
frost,” I spoke as an Englishman, and used the epithet relatively, 
without thinking how it might be understood by one accustomed 
to a colder climate. All I meant was a frost severe enough to 
form ice more than an inch or so thick. 
I will first give you the result of my observations, and then 
proceed to answer the questions which Mr. Langton proposes. 
On December 26, while skating for some hours on a pool in Hag- 
ley Park, Rugeley, I examined the ice carefully, but could detect 
no trace of the prismatic structure. The air bubbles, generally 
more abundant towards the lower side of the ice, were irregularly 
dispersed, and not in any way arranged in vertical lines, and the 
ice had its usual fracture. On Tuesday, January 3, and the follow- 
ing day, I again skated on the same pool, and could not ascertain 
that any noteworthy change had taken place during my absence 
in such parts of the ice as were free from snow. Then came 
a thaw, on the first day of which I visited the pool; the 
sloppy state of the surface, owing to the melted snow, made 
examination difficult ; but on breaking the ice, I detected oc- 
casional traces of the prismatic structure. On returning in the after- 
noon of January 7, I found that a slight frost during the morning 
had been sufficient to make the ice safe, though the surface was 
still wet in places. Now, however, there was a marked change 
in its appearance ; in many spots the delicate surface-reticulation 
caused by the prismatic structure could be detected ; small air- 
bubbles, as it seemed to me, were more numerous, and very many 
of them were arranged in vertical lines, which when produced, 
met the angles of the surface-polygons. Ina few cases they were 
not in vertical but in sloping lines ; here it was evident that 
from some accidental cause, the sides of the prisms had not been 
at right angles to the surface of the ice ; this, however, was rare. 
Everything that I saw convinced me that the lines of bubbles as 
a rule were the consequence of the prismatic structure, not the 
cause of it. The quantity of snow and sleet that subsequently 
fell made it impossible again to examine the ice satisfactorily 
before I left the neighbourhood, though I visited the spot more 
than once. Yesterday and to-day I have been examining the ice 
on a pond in the Botanic Garden here, which is gradually melt- 
ing away. It exhibits almost everywhere the delicate prismatic 
structure which I described last year. On withdrawing fragment 
NATURE 

| Feb. 9, 1871 

after fragment, one to two inches thick, from different parts of 
the pond, I found the surface covered with a most delicate 
reticulation, and the edges crenulated, as though the whole were 
a model of a sheet of columnar basalt. The distance between 
opposite angles of the surface-polygons was generally from } 
to + of aninch. Here and there the ice-slab was partially or 
wholly perforated, the surface-water having penetrated at the 
junction of a set of joints, and dissolved away more or less of the 
adjacent columns ; in not a few cases these apertures were poly- 
gonal, whole columns having perished. There were, of course, 
many air-bubbles ; but I could see nothing to lead me to sup- 
pose that they had caused the structure ; thousands more would 
have been required than I could discover, for in many places 
where the structure was very perfectly exhibited there was hardly 
a bubble to be seen. 
With regard to the first of Mr. Langton’s questions, “‘ Does 
ice contract on approaching 32° F.?” Jamin (‘Cours de Phy- 
| sique,” vol. ii. p. 108) states that it does; and though he does 
not mention either the amount of contraction or the point of 
minimum density, the former, from his illustrative diagram, 
appears not inconsiderable. (2.) ‘Do air-bubbles form 
from the first in vertical lines?” I should say not, as a 
rule. (3.) ‘‘Is there any indication, as the winter advances, 
of a re-arrangement of the bubbles, as that they run into each 
other, and get more and more ranged in vertical lines? » None 
that I can discover. (4.) ‘‘Is there any indication in the earlier 
stages of the ice that after a night’s hard frost the cracks seen on 
its surface spread through its substance?” I have not obser gp 
any. The fifth question I have not at present the means ©} 
answering; but that does not materially affect the point in 
debate. 
I may add that while visiting the Schafloch Glaciére, during 
the past summer, I noticed that, near the entrance of the cave, 
the ice everywhere showed prismatic structure, but that near the 
extremity, where the temperature was at the time about 30° F., 
there was little, if any trace of it. 
One word in conclusion to this long letter, on a point of 
practical importance. I am now convinced that this minute 
prismatic structure is the rule rather than the exception in a thaw, 
though it has hitherto been overlooked ; and that it is the chief 
cause of the ‘‘rottenness” in ice. When it has been set up, a 
slab of ice 5 or 6 inches square, and full one inch thick, can be 
broken across as easily as if it were a cake of bread ; and slabs 
little larger will snap in two when dropped flat on level turf from a 
height cf less than eighteen inches. Almost every thaw brings 
its melancholy tale of persons drowned while skating on ice 
which, though thick, proves on trial to be ‘‘rotten.” Ihave no 
doubt that in every one of these cases it had become 
prismatic. Therefore all who are about to venture on the ice, 
when a thaw is setting in, should look carefully for the signs of 
this structure, and if it is present keep their distance. 
T. G. BoNNEY 
St. John’s College, Cambridge, Jan. 17 

Coming Home from Sicily 
THE Eclipse Expedition has gone forth and returned, having on 
the whole been most successful in its observations. But never, 
perhaps, was science pursued under greater difficulties. The 
hot haste in which all the necessary preparations and arrange- 
ments had to be made and perfected before departure is already 
well-known ; the combination of circumstances which impeded 
our locomotion on the outward journey to Sicily; the slight mis- 
hap on the Brenner, and the unfortunate loss of the beautiful 
Psyche have been noised abroad, but the return journey was not 
accomplished without mishaps, although nothing has been said 
about them. The stars in their courses fought against Sisera 
nct more relentlessly than did the elements against us. 
The Eclipse over, with all possible speed we packed up our 
instruments and started for Naples, being anxious to hasten 
homewards. We reached Messina on Monday, 26th December, 
with the full intention of sailing immediately. But a sirocco 
prevailed, which snapped the telegraph cable to Naples, and 
prevented our finding out anything about the movements of the 
steamer. Daily we expected the arrival of one from some 
quarter or other which might take us back, but we hoped against 
hope that each day would be our last in Sicily. . It was not until 
late on Friday afternoon, Dec. 30th, that our hopes were 
answered, and we weighed anchor. 
In due time we reached Naples (after a rough passage), and 
