Moreover, on turning to the tables of conductivity and specific 
heat, I find for iron and bismuth— 
’ c Iron. Bismuth. 
Ratio of thermal resistances... ... Yeo. 6 
as epecihe Meats: .t. ce, | acy, SET 
The theoretical resultant effect would seem to be indicated by 
compounding these ratios, which would still leave a decided 
balance in favour of iron, 
It seems doubtful whether the law, distance of point of equal 
temperature from source cc (/ conduetiviry, holds good in the 
-case of bad conductors, and in any case it only applies when all 
parts of the bar have attained a constant temperature. 
I must apologise for asking for information on so small a 
matter, but I should especially like the experiment to succeed if 
Nature will kindly permit it. At the sane time, I hope that I 
-shal! not be accused of undue pessimism if I say that, according 
to my experience, the work of a natural science lecturer is 
simply a perpetus] struggle against the malice of Nature. 
Eton College, March 18 H. G. MADAN 
Rookeries 
‘CAN any of your readers kindly inform me how to establish a 
-rookery. 1 have tried | utting old nests into high elm trees, but 
they have not been taken to, although rovks are often in the 
+trees, THE MuG 
Trueloves, Ingatestone, Essex, March 21 
-A Means of Saving some Lives in Colliery Explosions 
WHATEVER brings about an explosion in a colliery, it appears 
that men often perish thereby not from burning, nor from injury, 
but from want of fresh air. It would now be easy, or might 
soon become so, for every collier, at a small cost, to keep near 
him always when at work, a little vessel full of compressed air, 
which being provided witha rather fine nozzle, and a sto,-cock, 
and a small piece of india-riubber tube, might be a sufficient 
deliverance for him in the moment of need, should he in an 
explosion have escaped violent injuries. D. Kuys JONEs 
= 
Carmarthen, March 24 
ECONOMIC GEOLOGY OF INDIA? 
I.—Precious Stones and Metals 
HE concluding volume of the Manual of the Geology 
of India was issued from the Calcutta Press towards 
sthe last days of 1881, and a supply of copies may now 
-any day be expected to arrive in London. This volume, 
published by order of the Government of India, brings to 
a worthy conclusion a most remarkable work, in which 
we find a general geological sketch map of nearly the 
whole of India, a descriptive account ot its various for- 
mations, and a_ history of those geological products 
therein found which are of importance to mankind. 
When we stop to think of the immense area explored, of 
the enormous amount of details that had to be collected 
and sorted, of the dangers and trials which were encoun- 
tered during the investigation of much of the country 
that had to be explored, we confess to being struck with 
amazement at the energy, zeal, and courage of the com- 
paratively very small staff employed by our Government 
in this service, and we feel sure that those labouring in 
European or American fields will be the first to acknow- 
ledge how much is owing to the Geological Survey of 
India for the quality as well as the quantity of the 
work done by them in the plains of Asia. 
but it is not only the geologists that will find an interest 
in this the third volume of the Manual. It treats of the 
economic products of the geological formations of India, 
and has a far greater interest even for the statesman than 
for the scientific man, and an interest too for the com- 
1A Manual cf the Geology of India. 
By V. Ball. M.A., U G.S., 
Survey of India. 
cutta, 1891.) 
" Part IIT. Economic Geology.” 
Owclating Deputy Super ntendent, Ge logical 
Pubtished by order oF the Government of India. (Cal- 
NATURE 
7 1a 
mercial man and the general reader, nay even more, 
there is much of interest in this volume for the student 
of history, for the student of mankind, about the origin of 
myths, and about the gradual development of the arts of 
working in iron and gold. 
This volume is written by Prof. Valentine Ball, who 
was, until recently, officiating deputy Superintendent of 
the Geological Survey of India; an author well known by 
his pleasant record of many years’ work in India, not lon 
since published under the title of “ Jungle Life in India,’ 
and one who, by many years’ assiduous and patient labour 
as one of the Survey Staff, was fully qualified for the 
great tas< so well accomplished in this work. Not only 
has he brought together in this volume a great store of 
facts collected by others, but from his own personal 
knowledge of localities and details, he has been enabled 
to arrange these facts in orderly sequence in a way few 
others could have attempted, and he well deserves the 
high commendation of his chief, the Superintendent of 
the Survey, who writes: “The student, as well as the 
man of enterprise, will long owe him gratitude for what— 
he has thus brought within their easy reference.” Ai 
To give our readers an idea of the contents of this 
volume, we propose to treat of them in a somewhat 
arbitrary fashion. In this notice we would call their 
attention to the Precious Stones and Metals of the East, 
In a second notice to treat of its Iron and Coal resources, ~ 
and of the important subjects of its Salt supply and 
Building Stones. It will not be in any sense our object 
to treat these subjects in an exhaustive manner, but to 
indicate to the reader what he will find in the 600 large 
octavo pages of this work, which is illustrated with 
numerous maps, lithographic plates, and woodcuts. 
The diamond is the most important of the precious 
stones of India; it can be traced back to Sanscrit litera- 
ture, in which the first mention of its actual localities is 
to be found. The famous Koh-i-nur is stated to have 
belonged to Karna. the King of Anga, about 5000 years 
ago; but this is not founded on any very reliable evi- 
dence. Tavernier and Marco Polo allude to a trade exist- 
[Marek 30. 1882 ; 
ing in diamonds between Asia and Europe, and before © 
the first diamond mines in Brazil were opened (1728) 
nearly the whole supply of the old world went from India, 
There are in India three extensive tracts, widely separated 
from each other, in which the diamond is known to occur, 
Besides these principal tracts there are others where 
diamonds have been found, but precise details are want- 
ing. The most southern of the three great districts has 
long borne the familiar name of Golconda, though Gol- 
conda itself never produced diamonds, and is in fact 
merely the mart where they were sold and bought. In 
this southern tract, which is in the Madras Presidency, 
either are or have been the mines of Kadapah, Bellary, © 
Karnul, Kistna, and Godavari. The second great tract 
occupies a considerable area between the Mahanadi and 
Godavari rivers. The third is situated in Bundelkhand, 
near one of the chief towns of which, Panna, some of the 
principal mines are situated. In Northern India the 
diamonds, when found 7z s/fz, are in a conglomerate 
which is referred to the Rewah group of the Upper Vin- 
dhyan formation, while in Madras they are found under 
tbe same circumstances in the Banaganpilly sandstones, 
which form the base of the Karnul formation. 
In connection with this geological position it is inte- 
resting to note that these Vindbyan rocks of India have 
been correlated with the diamond-bearing rocks of the 
Cape Colony in Africa. The examination of the diamond- 
bearing strata of India seems to throw no light on the as 
yet unsettled question of the conditions under which the 
crystallisation of carbon took place, which resulted in the 
formation of this precious gem, though synthetical ofera- 
tions in the laboratory seem to tend towards confirming 
Liebig’s view, that ic has been formed by crystallisation 
from a liquid hydrocarbon. It must however be remem- 
