May 2~ +880] 
NATURE 
33 
also seen another specimen of the same description. Ua. -- 
that these two specimens have been manufactured by Malays for 
whetstones out of the so-called thunder-stones? I cannot 
account for them in any other way; they are too slight for 
hammers. 
For my part, I have always found the Sakaies especially 
wanting in every respect as to traditions beyond the memory of 
their own generation, and they have invariably answered my 
inquiries as to the origin of the stone axes by saying, like the 
Malays, that they are thunder-stones. To such an extent is this 
belief held by Malays, that the other day a Malay of considerable 
social standing assured me that once a cocoa-nut palm was struck 
by lightning close to his house, and that about a month after- 
wards he searched about the roots of the tree and found the 
thunder-stone which was the cause of the damage: it was this 
man’s father who for several years kept a fire alight in his house, 
which fire was generated from the same tree after it had been 
struck by the electric current. 
I have already drawn attention to the Malay belief as to these 
so-called thunder-stones (NATURE, vol. xxxii. p. 626), My 
specimens are all in the Perak Museum at Thaiping. 
Kinta Perak, April 5 A. HALE 
On a Thermo-electrical Phenomenon in Connection with 
Prof. Balfour Stewart’s Paper on Terrestrial Magnetism 
In the Philosophical Magazine for May Prof. Balfour Stewart, 
in his paper ‘‘On the Causes of the Solar-Diurnal Variation of 
Terrestrial Magnetism,” takes in one place (p. 443), for an 
example, the case of ‘‘an ordinary electric circuit, say. of a 
circular shape, and horizontal, and heat it by causing some 
source of heat, such as a lamp, to travel slowly around it with a 
definite rate of progress.” He goes on to say that no current 
due to the heating will take place. So it would generally be 
thought. If, however, the experiment be even roughly tried, at 
all events with an iron or nickel wire, the contrary takes place. 
An account of the experiments, &c., which I have made on this 
subject, was read before the Royal Dublin Society on March 24, 
and will, in the course of time, be printed in the Society’s Pro- 
ccedings. Though there is a current in a wire on causing a 
heated portion to travel along it, it seems unlixely from the 
nature of the phenomenon that it could in any way be inferred 
that the higher air would similarly affect a current under the 
sun’s heating. FRED. S. ‘TROUTON 
Physical Laboratory, Trinity College, Dublin 
Do Migratory Birds Return to their Old Haunts? 
MucHu evidence has been given by naturalists to prove that 
birds of passage return to their old haunts. The following, I 
think, may be of interest to some of the readers of your valuable 
paper. For the past two springs a cuckoo gifted with a 
decidedly peculiar note has visited this neighbourhood. Within 
the last fortnight it has again arrived. Its song consists of three 
clear distinct notes, cuck—coo—coo, the second note being a 
semitone above the last. This it never varies. We all know 
that towards the end of its sojourn the cuckoo suffers from 
hoarseness, or, as the country people say, ‘‘ changes its tune.” 
Although this bird suffers in a similar way, yet it still maintains 
its peculiar song—three notes. As far as I can ascertain, it 
does not wander beyond the same limits—from the park here to 
alittle hill about half a mile distant. I think these facts not 
only conclusively prove that the cuckoo returns to its old 
quarters year after year, but that it also restricts itself during its 
stay in this country to the same locality. F.C. TAYLOR 
Summerleaze, East Harptree, May 13 
The Poison of the Stinging-Nettle 
IN the interesting article in your issue for May 6 (p. 5), on 
‘*Plants and their Defences,” there is one sentence on which I 
should like to be allowed to offer a few remarks. It runs 
thus :—‘‘ This fluid [of the stinging-gland of the stinging-nettle] 
is generally conjectured to be formic acid—a view based on the 
fact that this acid can be obtained from the nettle-plant by 
suitable means.” Does this ‘‘conjecture” rest on any other 
basis than the similarity of the effect produced by the sting of 
the nettle and the bite of the ant? I am inclined to think not. 
Certainly the fact that formic acid can be obtained: from the 
nettle-plant is not in itself a cogent argument, seeing that it has 
cell-sap Ot lVing ‘pianctd ic a wi F 
: ts 9 widely-sprez 
harmony with the fact that the fiuid coneaseConstituent of the 
glands of the nettle has frequently, if not always, an alkaline 
reaction. It seems strange that we have at present no trust- 
worthy observations on so interesting a question. Can none of 
our physiological chemists come forward and remove it from the 
region of conjecture ? ALFRED W. BENNETT 
St. Thomas’s Hospital, May 13 
What is Histioderma ? 
CAN any of the readers of NATURE inform me to what class 
of fossil organisms belongs the genus Histioderma? Mention 
of the name—but of the name only—is made by Sterry Hunt 
in this journal, vol. vi. (1872), p. 54, and by Hicks in the 
Quarterly Fournal of the Geological Society of London, vol. 
xxix, part I, 1873, table facing p. 42. It does not occur in 
Broun’s ‘Index Palzeontologica,” in Pfeiffer’s ‘* Nomenclator 
Botanicus,” nor in Scudder’s ‘* Zoological Nomenclator.” The 
name is not to be confounded with that of Carter’s genus, 
Histoderma, established 1874, for recent sponges. 
Leyden, May 15 
| ON THE INFLUENCE OF FORESTS ON THE 
CLIMATE OF SWEDEN}! 
/ANM BS 2URNE oe Report on this subject has been prepared 
by Dr. H. E. Hamberg, and printed as an appendix 
to the Report of the Forest Commissioners of Sweden for 
the year 1885. The observations were commenced in 
1876, on the principles established by Dr. Ebermayer in 
Bavaria, but Dr. Hamberg soon found that the mere com- 
parison of the results obtained at the forest station with 
those yielded by its sister station in the open country was 
insufficient to bring out all the peculiarities of forest in- 
fluence, and accordingly he added a third class of station, 
situated in a clearing in the forest itself (oppen plats z 
skogen). The various results of these observations are 
discussed in a very exhaustive manner, and we must refer 
those interested in the subject to the Report itself. The 
author’s conclusions, however, are very interesting, and are 
reproduced here in full. 
“Our researches do not allow us to determine whether 
the presence of the forests on the whole contributes to in- 
crease or diminish the quantity of heat in the atmosphere, 
that is to say, to raise or lower its temperature. In fact, 
we have been entirely unable to take into account either 
solar radiation or the radiation from the needles * and the 
points of the trees. Until we are able to ascertain the 
quantity of heat which escapes from these surfaces, and 
its relation to that escaping from other surfaces, it is quite 
impossible to determine with certainty the influence of the 
forest on such an important subject as the mean tempera- 
ture, and must confine ourselves to approximate estima- 
tions. Among the various surfaces which are met with in 
Sweden the most important are assuredly water, bare 
ground or rock, soil covered by herbage, and finally forest. 
Neither the surface of the lakes and sea nor the bare soil 
of town streets have any resemblance to the forest: the 
climate of the latter bears no similarity to a maritime 
climate or a town climate. A forest may best be con- 
sidered as an instance of vegetation on a gigantic scale, 
as is evident from the low temperature of the ground 
under the trees, and the freshness of the air in summer, 
especially in the evening and at night-time, thus affording 
evidence of active radiation. In this case the forest would 
be a source of cold rather than of heat. But here we are 
simply dealing with suppositions. 
“From this point of view a forest is distinguished from 
all the other surfaces we have mentioned, in that it extends 
into a stratum of air lying far above that in which man 
lives and carries on all of his occupations which depend on 
t ««Om skogarnes inflytande pa Sveriges klimat.” From Quart. Journal 
Roy. Met. Soc. for April 1886, communicated by Mr. R. H. Scott, F.R.S. 
? The forests dealt with were entirely of pines and firs. 
