228 
NATURE 
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[Fuly 17, 1873 
exists there, aboye clouds transformed by the syn into 
flakes of light, adds to the beauty of the spectacle, and 
fills the soul with inexpressible admiration. 
We do not yet know exactly to what cause to attribute 
the production of a luminous contour around the shadow 
projected upon vapours or mists. Some observers have 
thought that these phenomena are due to the diffraction of 
light, but it is possible that they have a common origin 
with the rainbow. What tends to confirm this opinion is 
the necessity for the presence of the vapour of water as a 
neccssary condition of the phenomenon: if it is the 
result of diffraction, it ought to appear as well upon a 
white wall, or any kind of screen, as upon a cloud. It 
is possible, moreover, to study these curious phenomena 
by means of experiments upon the earth; by suitably 
arranging screens of silk or muslin saturated with water. 
which resemble a cloud, we may expect to be able to pro- 
duce the phenomenon. M. Leterne points out another 
excellent method of studying it. On a spring morning, 
when the sun, about 15 or 20 degrees above the horizon, 
has warmed the atmgsphere a little, and has produced a 
light condensation of vapour upon the grassy borders of 
the oads, ene may see his silhouette projected upon 
the humid yerdure, surrounded by a luminous con- 
tour, in which is seen the colours of the spectrum, the 
red, however, being strangest.* 
THE GEOLOGICAL SURVEY OF INDIANA 
‘EOLOGY is a branch of Science which specially 
commends itself to the fostering care of Govern- 
ments, paternal or otherwise. More particularly is this 
frue of a new country, where, in the imagination of the 
settlers, untold wealth has yet to be dug out of the earth, 
if only they could discover in what quarter best to look for 
it, Accordingly, in not a fe of dur colonies and in a 
RHEE of the States of the Union, geqlagical and mine- 
ralogical surveys have long been at ore, originated and 
continued at the public expense. In most cases, of 
course, the first aim of such suryeys, an ; 
ustification of their existence in the eyes of practical and 
y NO means scientific legislators, is the finding of mineral 
weathe If they were begun from the lofty scientific point 
of view they would fail, and deservedly. But whena really 
able scientific man gets the charge of one of them, and 
has at the same time that mother-wit and knowledge of 
the world which scientific men so often lack, he may not 
only attend to the rigid economics of his paymasters, but 
do great service to geology. His aim is to show the 
public that a strictly scientific basis is the only one on 
which a mineral survey to be of any value can be con- 
ducted. And this is so obvious that if it is simply and 
clearly stated, it for the most part commends itself to the 
common-sense of public men. In laying this necessary 
basis and then in carrying out the survey for economic 
minerals the geologist may both pave the way for an 
enormous increase to his country’s industry and wealth, 
and add much of permanent interest and importance to 
the common stock of geological knowledge. 
Perhaps the most notable illustration of the successful 
accomplishment of this double mission is furnished by 
the career of Sir William Logan, whose practical kindly 
ways enabled him to triumph over the shortsightedness 
of colonial gbstructionists, and whose patient and saga- 
cious labours among the racks of Canada have made his 
name honoured and familiar all over the world, and have 
conferred distinction also upon his country. In the United 
States, too, fostered by the liberality of the Legislatures, 
a number of admirable State surveys have been made, or 
are still in progress. Under the auspices of such men as 
James Hall, Owen, the Hitchcocks, the brothers Rogers, 
Hayden, Whitney, Blake, Cook, and others,’ not only 
have maps been constructed, but elaborate reports have 
" Comptes Rendus, t. \xxvi. p. 786. 
in fact the very . 
heen published, embracing, in addition to the paramount 
economics, much yalyable information in geology, mine- 
ralogy, and palzontology. 
One of the latest of these State suryeys is that of In- 
diana, which was started some four years ago under the 
direction of Prof E. T, Cox. Like those already referred 
to, it was organised by the authorities “for the purpose 
of collecting information designed to promote the inte- 
rests of agriculture, arts, manufactures, and mining.” 
But it was furnished at the same time with an analytical 
laboratory “for analysing such ores and substances as 
may be deemed useful to the State,” and with space “ to 
build up a geological and natural history cabinet,” while 
in order to render its labours as speedily serviceable as 
porsible, an annual report of progress was required to be 
issued. 
Prof. Cox has evidently a hard task before him. He 
has been invited to become a kind of depository of all 
the mining information in the State. He is to see that 
trustworthy mineral surveys are made, and at the same 
time he is expected to look after the laboratory and infant 
museum at Indianopolis and—perhaps most laborious 
but not least useful of all—to receive everyhody who 
wants to know about coal, iron, or other mineral produce, 
and to collect and furnish to such inquirers all the infor- 
mation procurable, He generously says in one of his 
reports that this latter part of his duties “has always 
given him pleasure,” though he confesses that it has con- 
sumed a considerable portion of his time. Fortunately — 
he can count on the help of a small but apparently able — 
staff of assistants, and notwithstanding all the obstacles 
in his way he has succeeded in getting through a large 
amount of work which, though not yet of high scientific 
value, must bear most importantly upon the future deve- 
lopment of Indiana. 
Three volumes of reports with maps have been 
published, bringing the account of the progress of the 
Survey up to the end of last year. Each of these neatly 
printed and not too bulky octavos describes several 
counties of the State with reference chiefly to the dis- 
tribution of economic minerals ; and the maps which ac- 
company it, though roughly and cheaply executed, are 
clear and must be of infinite service to the many specula- 
tors and others who every year come in increasing 
numbers into the state in search of mineral investments. 
The coal-field of Indiana, though only a part of the larger 
basin of Illinois, is estimated to equal more than half of 
the area of the whole of the coal-fields of Great Britain 
and Ireland. Some of the coal-seams are of excellent 
quality, specially that known locally as “bleck-coal,” 
which is said to be unrivalled for iron-furnaces. Abun- 
dant iron ore likewise occurs, Hence not only coal-pits 
but iron-works are springing up in rapidly increasing 
numbers. Not a little of this wonderful rapidity of growth 
is attributed by Prof. Cox, and no doubt justly, to 
the extended and more accurate knowledge of the 
minerals which the Survey has been able to publish. In 
the course of two or three years tracts of “ primeval forest” 
have vanished, and in their place the visitor would now 
see clanking engines and mining villages, crowded with a 
population as busy and begrimed as any to be met with 
in Staffordshire or Lanarkshire. And yet vast though 
this change is, it may be said to have only just begun. 
Before many years are over the coal-bearing part of the 
formerly quiet agricultural state of Indiana will become 
one of the most active centres of industry in the Union, 
with railways diverging in all directions to carry away 
its mineral produce. ; ‘ 
Prof. Cox and his assistants have not only been success- 
ful in pointing out the mineral resources of the various 
coynties. In looking through his reports one can see 
that he continues from year ta year to slipin more of 
general scientific interest. This is notably the case with 
the volume lately published. In addition to a series of 
