SCIENTIFIC SUMMARY. 
421 
in the tube when the temperature rose and the atmospheric pressure was 
reduced. It seemed, therefore, that increased pressure caused the water 
to ascend, whilst increased temperature caused its descent ; so that, when- 
ever both these agencies were at work, the alteration in the height of the 
water depended upon which of the two was superior. Herein, then, lay 
the cause of the discrepancies. If the temperature was constant, the 
weather-glass of Galileo would be a faithful instrument ; but as the tem- 
perature does not always correspond to the pressure of the atmosphere, 
the elevation of the water in the stem could not be constantly propor- 
tionate to the density of the external air. — See a most interesting article 
in the Chemical News , February 6, 1864. 
The Boiling Points of Mixed Liquids are regarded by M. Alluard as being 
by no means tests of their purity. When ether is mixed with one-tenth 
of its weight of sulphide of carbon, it boils at the same temperature as 
pure ether. In order to discover the purity of a liquid, the static and 
dynamic methods of Regnault’s process must be employed. By the 
adoption of this means, the presence of the -njVffth of a substance, added 
to alcohol or sulphide of carbon, may be detected. — Vide Comptes Rendus , 
lviii. No. 1. 
Optical Properties of Azulene. — The latter term is applied to designate 
the principle contained in two peculiar blue oils, obtained from Achillea 
and Matricaria , two genera of the natural order Compositse. This prin- 
ciple has been submitted to spectrum analysis by Sir David Brewster, 
who states that the two oils differ from all the various bodies which he 
has yet examined. Between the two lines A and B of Fraunhofer’s 
map of the spectrum, the two ottoes absorb the light in these portions 
more powerfully than in the portions adjacent to them. No other fluid or 
solid upon which he has experimented acts in a similar manner ; but 
what is exceedingly remarkable is the fact, that the earth’s atmosphere 
exerts a similar action when the sun-light passes through its greatest 
thickness, as at sunrise and sunset. 
Temperatures at which Metals boil . — These have been hitherto determined 
by means of an air pyrometer, but M. Becquerel has adopted another 
method for their determination. The instrument he employs is a thermo- 
electric pile, and with it he found that the following metals boil at the 
following degrees centigrade : — cadmium 720°; zinc 920°; silver 916°; 
gold 1,037° ; palladium 1,360° ; platinum 1 ,480°. It is of some importance 
to state that certain of these figures are lower than those obtained by 
M. Becquerel, when using the air pyrometer. — Vide Comptes Rendus , 
lvii. No. 21. 
Iron at a high Temperature penetrated by Gases. — M. Cailletet recently 
laid before the French Academy a resume of his experiments on the per- 
meability of heated metals by gases. He points out that the bullae or 
cavities, found in iron, originate in this manner. The gases proceeding 
from the fire permeate the iron, and occupy the cavities. In order then to 
prevent the formation of these cavities, it will be necessary to have the 
fires and metal so related that no vacuum may be formed in the latter. 
Luminosity and Temperature of Bodies. — From an extensive series of 
physical and mathematical researches, M. Provostaj'e draws the following 
VOL. III. NO. XI. 2 F 
