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POPULAR SCIENCE REVIEW. 
woodcut of the spectrum) in Scientific Opinion, states that Mr. Winder 
had submitted the aurora to careful spectrum analysis, and by a peculiar 
arrangement of the slit of his spectroscope had succeeded in obtaining a 
beautiful spectrum, consisting of one very bright line in the yellow, and 
one of less brilliancy in the green. The bright line was close to the sodium - 
line d, and coincident with an air-line which appears in the solar spectrum 
when the sun is near the horizon. The pale line in the green he failed to 
identify as belonging to any known substance. 
Influence of Different Coloured Lights on Mineral Oils. — M. Grotowsky 
publishes some curious results in the Moniteur de la Photographic. The 
conclusions are as follows:— 1. The photogenic or solar oil preserves all its 
properties intact when inclosed in iron barrels. 2. When inclosed in vessels 
of white glass and protected by straw, little and but slightly inj urious modi- 
fication was apparent. 3. Vessels of white glass painted black were not 
sufficient to protect the oil from absorbing traces of ozone, but the stoppers 
were not attacked. 4. Vessels of white glass, unprotected. — In these the 
oil became much charged with ozone, and burnt very badly : in colour it 
became of a very marked yellowish tint, and its density increased by (M)03. 
5. Vessels of green glass, unprotected. — The oil became charged with ozone, 
but burnt well notwithstanding ; the cork stoppers were attacked, and the 
colour of the oil became modified. 6. Vessels of green glass, painted black. 
— Ozone was absorbed, but no apparent modification was appreciable. 7. 
Vessels of green glass covered with straw. — Traces of ozone were apparent, 
and the oil assumed a slight yellowish tint. No defect was, however, to 
be observed in burning. 8. American petroleum inclosed in vessels of white 
glass, unprotected, was much charged with ozone, and would scarcely burn 
in consequence ; it became of a yellowish tint, and its specific gravity was 
augmented by 0-005. 9. The same oil screened from the access of light 
underwent no change. 
An International Meter. — At the meeting of the Acaddmie des Sciences of 
Paris on Oct. 25, M. Dumas made some observations on a letter received 
from M. Jacobi, in which the Russian savant announced that there had been 
received an official reply from the Academy of Berlin to that of St. Peters- 
burg. The Berlin Academy is in agreement with that of St. Petersburg 
and that of Paris in regard to the necessity of employing the mhtre in the 
Archives of the latter ; but it suggests that there should be prepared, under 
the inspection of an international commission, a number of exact counter- 
parts which would serve as standards for the future. 
The Ratio- Micro- Polar iscope is the name given by Mr. J. J. Field to 
an ingenious contrivance for exhibiting the effects of polarised light under 
the microscope. Its description is too detailed for insertion here, however. 
The object of the inventor is to obtain a plan by which a definite effect with 
selenites may be always had. This he achieves by a combination of toothed 
wheels numbered so that the actual revolutions made in obtaining any sepa- 
rate tint are recorded, and thus in future observations the difficulty of experi- 
menting with any particular colour is obviated. — Journal of Quekett Club , Oct. 
Absorption of J/ydrogmium by Iron precipitated by Electricity. — The Che- 
mical Xeics (Dec. 17) in one of its recent summaries gives an abstract of a 
paper on the above subject by M. Jacobi of St. Petersburg. Iron obtained 
