384 
previously published investigations into the theory of earth- 
quakes” (p. 260). The reviewer may not have been able or not 
taken the trouble to distinguish the old from the new; but as a 
fact, the greater part of those forty-six pages is of matter never 
' before published. 
So aiso it is scarcely candid to object that “no reference 
is found to any of the Continental men of science who have done 
so much for terrestrial vulcanicity,’’ which is contrary to the fact, 
for I have referred by name or by their labours to the few who 
have in any way advanced our knowledge as to the nature and 
origin of volcanic heat, without noticing that within that scope only 
was I by space obliged to confine myself, as stated in pp. 48, 49, 
54,76, &c. ; the phenomena occurring at volcanic vents, which have 
chiefly engaged the attention of Continental and all other vol- 
canic authors being avowedly outside my limits, and, I might add, 
but too often of secondary importance. 
The nomenclature generally of my ‘ Translation of Palmieri” 
is said to be objectionable, because such terms as sulphide of 
potass and terrochloride of ammonia are encountered. I have 
looked through the pages since without being able to discover 
these dreadful terms. However Iam ready to take the reviewer's 
word that such a slip in proof correcting may be found in some 
place, and I humbly bow to such microscopic, profound, and 
valuable criticism, though, as stated, the conclusion is a good 
deal wider than its premises. RopertT MALLET 
Enmore, The Grove, S.W., March 5 
Effect of Resistance in modifying Spectra 
In a review of M. Guillemin’s work ‘‘The Forces of 
Nature” which appeared in last week’s Asheneum, the fol- 
lowing reference, by M. Guillemin, to the experiments of 
M. Mitscherlich is quoted : ‘* Suivant ce physicien il arrive que la 
presence de certaines substances dans une flame a pour effet 
d’empecher de se produire les spectres des autres substances, 
d'enteindre leurs raies principales.” The English editor adds 
that the effect ‘‘ may probably be explained by the observations 
of Frankland and Lockyer.” 
In relation to this subject of the extinction of the bands of one 
metal by another, you will perhaps permit me to quotea paragraph 
from one of the lectures which I have recently had the honour of 
delivering in the United States. The ares of thallium and silver 
had just been compared, and their similarity of colour po'nted 
out. The power of prismatic analysis to show that, notwith- 
standing the apparent identity of colour, the arcs really belonged 
to two different metals, was then demonstrated. The metals 
were afterwards subjected /ogeter to the action of the Vol- 
taic current, and it was sbown that the band of thallium fell mid- 
way between the two bands of silver. Hence the similarity of 
colour. ‘The lecture then proceeds thus :-— 
“But you observe here another interesting fact. The thallium 
band is at first far brighter than the silver bands ; indeed the 
latter have wonderfully degenerated since the bit of thallium was 
ut in. The reason of this is worth knowing. It is the resistance 
offered to the passage of the electric current from carbon to 
carbon that calls forth the heating power of the current. If the 
resistance were materially lessened, the heat would be materially 
lessened ; and if a// resistance were abolished there would be no 
heat at all. Now thallium is a much more fusible and vaporis- 
able metal than silver, and its presence facilitates the passage of 
the current to such a degree as to render it almost incompetent 
to vaporise the more retractory silver, But the thallium is gra- 
dually consumed ; its vapour diminishes, the resistance conse- 
quently rises, until finally the silver bands are rendered as bril- 
liint as at first.” 
In the spectra of mixed substances derived from the electric 
spar the action here referred to must come frequently into play. 
| Ant See ae Me 
pat fens 1" cl 
Le eae eT 
NATURE 
If neither the fact, nor its proposed explanation, be new, I would 
thank you to commit this documeat to your waste-paper 
basket. Joun TyNDALL 
Royal Institution, March 1873 
Perception in the Lower Animals 
THE theory of taking olfactory notes by the way, as suggested 
by Mr. Wallace in explanation of the faculty possessed by ani- 
mals of finding their way home, seems to meet with general 
acceptance amongst your correspondents ; yet it totally fails to 
account for those instances in which the animal finds its way 
back by quite a different route to that by which it was taken away, 
(Mar. 20, 1 
A good example is given by “F. R. G. S.,” in the last num- 
ber of NaTurRE; the anecdote of his riding-horse, by Mr. 
Darwin, also seems to illustrate this point. In an article on the 
‘Consciousness of Dogs,” in the Quarterly Review, of last 
October, the following remarkable instance, amongst others, is 
mentioned on indisputable authority. A hound ‘ was sent by 
Charles Cobbe, Esq., from Newbridge} county Dublin, to Moy- 
nalty, county Meath, and thence, long afterwards, conveyed to 
Dublin. The hound broke loose in Dublin, and the same morn- 
ing made his way back to his old kennel at Newbridge, thus 
completing the third side of a triangle by a road he had never 
travelled in his life.” 
Nowas Mr. Wallace’s theory does not explain these and similar 
instances, it clearly cannot be received as a solution of the question. 
Moreover, not only does the faculty exist in other animals not 
remarkable for their sense of smell, but we find it in cases where 
this sense has nothing to do with it. Take, for example, 
the direct homeward flight of the carrier pigeon. Under the 
same head may be brought the migrations of birds and fishes, and 
the habits of the turtle, as mentioned by Mr. Darwin. 
The writer in the Quarterly suggests a sense of the magnetic 
currents of the earth—a sort of internal mariner’s compass in 
fact. But it is difficult to see how this could have helped the 
dog to find its way from Dublin to Newbridge, for instance, 
unless it was also able to consult a map so as to ascertain the 
relative position of the two places. 
It seems then that the problem still remains unsolved. Either 
we must extend almost indefinitely the range of smell and sight ; 
or, we must suppose the existence of some peculiar sense of the 
nature of which we are ignorant, which enables its possessor to 
retain, as F. R. G. S. expresses it, ‘fa constant perception of 
the bearing of its old home.” a, 
Bath, March 17 
POSSESSION ISLES 
AS the idea of occupying Possession Islands as a 
station for observing the Transit of Venus has 
been lately propounded, I have been requested to com- 
municate to NATURE the results as to its climate, which we 
have obtained in this office from the logs of H.M.S. 
Erebus and Terror, which we are now re-discussing with 
a view to publication. 
Possession Isles are in lat. 71° 56’ S., long. 171° 7 E. 
H.M.S. Erebus and Terror were within lat. 70° to 724° S., 
and long. 170° to 175° E. from rothto 17th January, 1841. 
During these eight days the mean height of the barometer 
was 29°143, mean temperature of the air 29°’7, and of the 
sea 30°'5 ; the wind was variable, but chiefly from S. and 
SSW., force 6; the weather was clear ten times, cloudy - 
twenty times, overcast eighteen times, from forty-eight 
double sets of four-hourly observations, while snow. was 
noted nine times, and squally weather ten times. 
The ships were within the same area on 2oth and 21st 
February, 1841 ; and, during these two days, the mean 
height of the barometer was 28°920 inches, mean tempe- 
rature of the air 23°°5, of the sea 30"1 ; wind WSW. to 
SE., force 9 to 5 ; the weather was cloudy and overcast. 
In addition I am permitted to enclose a letter from Dr. 
Hooker, which he kindly sent me in reply to my inquiries 
as to his reminiscences of his visit to these inhospitable 
regions, and which he has allowed me to publish. 
Meteorological Office ROBERT H, Scorr 
Letter from Dr. Hooker 
Possession Island, or rather Possession vock, is in a 
very inaccessible position. The chance of landing a well- 
equipped party upon it when reached, and the proszect of 
its subsequent removal by ships, if landed on, is very 
small. In any case I feel little uncertainty as to what 
would be the fate of a party left there for the winter, and 
the prospect of their seeing the transit would be abso- 
lutely 227, 
To reach it we “took the pack” January 3, 1841, and 
had not penetrated it till the 9th, aided at last bya furious 
gale. We then discovered South Victoria, and traced its 
coast from lat. 703° to lat. 78°, without finding a spot 
where it was possible to approach the shore, During the 
ars 
it 
ES —— a ee 
ie wate 
OE ee 
—  —_ ee oo 
