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Dee. 1, 1870] 
NATURE 
83 

1858.— Liais at Paranagua. Instrument used, a Savart’s 
polariscope. He found the plane normal to the limb of 
the sun, and the intensity small, but greater than that of 
the moon. 
He also remarks that the neutral point of sky polari- 
sation was in the neighbourhood of the sun, a statement 
difficult to comprehend, as the neutral points are com- 
monly defined by their distance from the sun, 
1860.—Secchi on Mont St. Michel. Used an Arago’s 
polariscope, and found that the images were not of equal 
colour, and that one was elongated in one direction, the 
other in a direction perpendicular to it. This last appear- 
atice was probably imaginary, as the crystal in the polari- 
scope would prevent the extinction of any polarised rays. 
1860.— Pragmowski at Briviesca. Used a plate of right 
and left-handed quartz at the common focus of the object 
glass and eye-piece, and a Nicol’s prism in the eye-piece. 
This combination should give two semicircles of comple- 
mentary tints when the plane of polarisation is oblique to 
the line of junction of the quartz. Using a power of 22, 
placing the line of junction vertical, and bisecting thesun, 
he found the top and bottom alone of uniform tint, the 
two semicircles being very strongly coloured, one red, the | 
other green. He thence inferred a radial polarisation. 
In reality, in this case, he should have found the sides 
alike, as well as the top and bottom, only faint yellow 
instead of purple, and the colours most strongly marked | 
at angles of 45°. 
1868.—Campbell used a Savart’s polariscope and found 
the bands strongly marked, having a maximum at 140° 
from the vertex. 
1868.—Winter used a similar instrument, and, as a re- 
sult, found the polarisation very strong, especially close 
to the sun. 
1869.—Pickering at Mount Pleasant. The writer used 
an Arago’s polariscope, and found the sky polarised close 
to the corona, the plane being the same on all sides of 
the sun. 
1869.—Smith, at Eden Ridge, records a similar result 
obtained by a member of his party. 
We see, therefore, that the results are very variable, 
the polarisation of the corona, if any, is obscured by that 
of the sky, probably due to secondary reflection, It is 
therefore very desirable to use some means of neutralising 
this effect. One remedy is to place a double-image prism 
in front of the telescope, which thus superposes two 
images of the sky polarised at right angles. For obser- 
vations on the sky no telescope should be used, or the 
light will be too much enfeebled. A Savart’s polariscope 
is the most delicate instrument, but such a one as the 
Arago is more useful to determine just what portion of the 
light is polarised. The Nicol’s prism and the double- 
image prism give such indefinite results, that little could be 
expected of them, and they have been tried by several ob- 
servers without success. The best instrument to measure 
the intensity of the polarisation is the polarimeter, consist- 
ing of several glass plates, which can be set at an angle in 
front of a Savart, and the point of disappearance of the 
bands recorded. The absence of polarisation of the 
protuberances has been observed by Abbadie, Pragmowski, 
and others, and seems so well determined, their further 
examination is unnecessary. 
EDWARD C. PICKERING 

THE RESOURCES OF VEARPEATA 
The Mineral and other Resources of the Argentine Re- 
public. Published by special authority of the National 
Government by Major I. Rickard, F.G.S. (London : 
Longmans and Co., 1870.) 
NM AJOR RICKARD has executed inavery creditable 
manner the task which the National Government 
deputed him to perform, and his volume will give its 
readers considerable insight into the vast material 
resources of the Argentine Republic. Hitherto La Plata, 
in spite of its name, has been regarded rather as a field 
for agricultural enterprise than as a source of mineral 
wealth; and the stories which were once current of 
mountains rich in precious metals have been forgotten in 
the details given by our countrymen of their successful 
farming in the pampas of the south. Various causes 
have combined to divert attention from the mineral riches 
of the country. The tedious contest with Lopez, only just 
concluded, and the turbulent character of the gauchos and 
Indian tribes, have checked the growth of confidence in 
the minds of emigrants or caritalists ; and though the 
vigorous administration of President Sarmiento has 
already done much to remove these obstacles, some time 
must still elapse before investors will be persuaded that 
“the great Republic of the South” is likely to realise all 
the favourable vaticinations of which Major Rickard 
makes it the subject. What, however, has most retarded 
the progress of mining, and, indeed, of all industrial 
enterprise, in the Argentine Republic, has been the defi- 
cient population and the want of means of intercom- 
munication and transport. Buenos Ayres and the other 
riverine provinces, where grazing is a pleasant and profit- 
able pursuit, absorb nearly all the working power of the 
Republic, and at the present time not more than 2,687 
persons are engaged upon any form of mining industry. 
If the reader will cast his eye over a map of the country 
(the absence of which in Major Rickard’s book is a serious 
defect), he will see what a mere scratching of the soil can 
be effected by such a handful of men. Hence it is that 
very trifling results have hitherto been obtained from the 
few mines yet in operation, and that the processes for 
reducing the ore have remained defective and costly. 
The supplies drawn from the Argentine Republic produce 
no appreciable effect upon the metal markets of the world, 
and in popular estimation its exports solely consist of 
tallow, wool, and hides. 
President Sarmiento,a man of no common discern- 
ment, is convinced that the substantial wealth of his 
country is to be found in its mineral resources, and, more- 
over, that they will provide the surest means for promoting 
rapid and extensive immigration. In their development 
is bound up the extension of commerce and the progress 
of agriculture. Had it not been for the discovery of gold, 
California might still have remained a vast cattle range to 
this day; and what is there to prevent La Plata, which can 
| boast of the riches of Copiapo, Potosi, and Famatina, 
from rivalling her neighbour in wealth, population, and 
national importance? 
The Argentine Republic is divided into fourteen pro- 
vinces, and extends southwards from the Tropic of Ca- 
pricorn to the goth parallel of latitude. Roughly speaking, 
| the characteristics of the country admit of a two-fold 
division ; the northern and eastern provinces being 
