April 12, 1883 | 
figures are also given in the standard works of Westwood and 
Packard on insects. As W. E. L. is probably a practical man, 
he will do well toconsider the proofs afforded by Mr, Elliot that 
the ‘‘ked,” as they call it in Scotland, is anything but the harm- 
less insect which some people imagine it to be. 
T. SPENCER CORBOLD 
I AM inclined to think your correspondent W. E. L., on the 
subject of “ticks” (p. 531), may have confounded two quite 
distinct animal forms under that name. The sheep-tick or louse, 
as shepherds call it, found at the roots of the wool on sheep, 
and which Ii ave often formerly had brought to me under one of 
those names, is an aberrant form of Azppodbosca, a genus of 
dipterous insects, the typical species being the well-known forest- 
fly. An excellent figure of the sheep tick will be found in 
~ Curtis’s ‘‘ British Entomology,” PJ. 142, under the name of 
Melophagus ovinus. 
Ixodes is a genus of the Acaridee, a group easily distinguished 
from the true insects by their having eight legs in the adult 
state. Six British species of Zxvodes are described by Dr. Leach 
in vol. xi. of the Linnean Transactions, There are probably 
others not as yet determined. The one best known is the com- 
mon dog-tick, found in a free state in woods and plantations, 
and attaching itself not merely to dogs but to hares, &c., and 
especially to hedgehogs, which often abound with them, the ticks 
getting their hold as the animals pass through the close grass. 
After attachment they soon get gorged with blood, their abdo- 
mens swelling to an immense size com) ared with the insignificant 
appearance of them previous to attachment, But I can remem- 
ber no instance of an Ixodes found ona sheep, though I would 
not undertake to say they never occur on that animal. 
Bath L, BLOMEFIELD 
Helix pomatia, L. 
I AGREE with Mr. Gwyn Jeffreys (NATURE, p. 511) in con- 
sidering Hedzx fomatia as indigenous in this country, and not 
introduced by the Romans. I never found or heard of a single 
specimen, either living or dead shell, being met with in the 
neighbourhood of Bath, which the Romans occupied for more 
than 400 years, though it is found in one or two localities in the 
adjoining county of Gloucestershire, from whence we have 
specimens in the museum of the Bath Literary Institution. 
Bath L, BLOMEFIELD 
Braces or Waistband? 
HAVING worna Spanish sash for some time many years ago 
while walking in the Pyrenees, I am decidedly of opinion that 
the weight of the trousers is supported much more easily and 
pleasantly by a sash than by braces; these last are narrow, 
about 2 inches wide, and though custom enables us to wear 
them without conscious inconvenience, I think any one using them 
for the first time would find them very unpleasant. The sash 
worn by the middle and lower class in Aragon is of wool 8 
or g inches broad, and (if my recollection is correct) about 
43 feet long; when of such width and length it does not need to 
be drawn “ght, but only closely wrapped round the waist and 
the end tucked in. I should certainly wear one constantly but 
that I do not wish to have an eccentric appearance. Medical 
men, I believe, attach great value to the wearing of sashes or 
bands round the stomach, especially in hot countries. A narrow 
silken sash which must be drawn tight is, I should suppose, far 
less pleasant to wear. 
SOLAR RADIATION AND GLACIER MOTION 
je the paper on the “ Mechanics of Glaciers,’ which 
the author had the honour to read before the Geo- 
logical Society of London in December last, it is stated 
that, after all allowance is made for work within the glacier 
due to the potential energy of the wezg/t of the ice-mass, 
‘there remains to be accounted for a secondary dif- 
ferential motion, which has, it appears, not yet received 
a satisfactory explanation . . . the movement is greater 
(a) by day than by night, (4) in summer than in winter.” 
The present paper is intended as nothing more than a 
brief statement of the experimental evidence, upon the 
NATURE 
553 
strength of which the explanation offered in the paper 
referred to has been put forward. I may say ex passant 
that this investigation was suggested to me bya statement 
of Dr. Croll’s (‘Climate and Time,” p. 519) that, “We 
find that the heat applied to one side of a piece of ice will 
affect the thermal pile on the opposite side.” It occurred 
to me that the looseness of this statement was quite in 
keeping with the zphysical notions upon which the 
writer has built up what he styles his ‘‘ molecular theory ” 
of glacier motion, and I set to work therefore to inves- 
tigate its accuracy. 
The principal apparatus used consisted of a delicate 
galvanometer, and a thermopile of a pretty high degree 
of sensitiveness, made up as it is of eighty-one couples of 
bismuth and antimony; the measurements were read off 
numerically by the light reflected on the scale as usual. 
Suspecting that the fallacy of the statement referred to 
lay in overlooking the effect of luminous energy, which of 
course is capable of passing through any /ransparent 
body, I made a few preliminary trials with glass and water, 
not having ice then at hand. A beam of solar radiation, 
having passed through two inches of distilled cold water 
+ half an inch of glass, was allowed to fall upon a 
Crookes’ radiometer ; this made the vanes rotate too fast 
for their rotations to be counted, even when the instru- 
ment was enclosed in a wooden case on all sides except 
that open to the glass-water screen through which the 
sunshine passed. A beam of solar light, having been 
sifted of its dark heat-rays in the same manner as before, 
was received upon the absorbing face of the thermopile, 
producing a considerable deflection of the magnet in the 
galvanometer, even with the feeble sunshine of our recent 
December days. 
The next step was a series of trials with zce itself. In 
the first instance, trials were made with the plates of ice 
im contact with the metallic face of the pile, the black 
(absorbing) face being placed at a distance of 3 inches 
opposite a large Bunsen flame in a room free froms trong 
draughts : in this way a constant difference of 36° C. was 
obtained for the opposite faces of the pile, and main- 
tained for more than half an hour, with the needle of the 
galvanometer quite stationary. An iron ball 3 inches in 
diameter, having been heated to dul! redness (clearly 
perceptible in a dark room), was placed opposite the 
plate of ice (1 inch thick) in contact with the pile, and 
allowed to cool. It was again heated as before, and 
placed at a distance of /ess than an inch from the ice 
(now less than half an inch thick), and allowed to cool. 
In both cases the effect observed upon the galvanometer 
was absolute nil, even when, in the second trial, the ice 
had become so thin by melting as to break under the 
small force required to hold it against the pile. 
In the next series of trials the arrangement was re- 
versed, the zce being placed just in front of the condensing 
cone attached to the absorbing face of the pile at a 
distance of 4 inches; the metallic face of the instrument 
was maintained at a constant temperature by contact 
with a vessel of cold water, whose temperature was ob- 
served frequently, and found to be practically constant. 
On the distant side of the ice was placed a double board- 
screen, with air-space and a circular hole to allow the 
passage of a cylindrical beam of radiation of the same 
diameter as the condensing cone. The iron ball, heated 
to dull red heat as before, was placed opposite the hole 
of the screen, at a distance of 74 inches from the face of 
the pile, the intervening ice-plate in this case being 1 inch 
thick, and the galvanometer having been stationary for 
half-an-hour before the experiment was made. Under 
the same conditions the experiment was repeated (1) with 
1-inch plate of ice; (2) with 4-inch of pond-ice + wet 
half-melted snow ; (3) with §-inch of fresh-fallen snow. 
In all these cases the result of the obscure radiation from 
the ball upon the galvanometer was adsolude nil, although, 
without the interposition of ice or snow, the maximum 
