SCIENTIFIC SUMMAEY, 269 
directions after the interruption of the current, the magnetism produced by 
the first twisting diminishes rapidly. 
If a voltaic current be transmitted through a magnet in the direction of its 
axis, the magnet will twist. 
The Dip of the Needle in London. — General Sabine has shown that there 
has been a gradual diminution of the dip in this city during the last forty 
years. The following table shows the rate at which this has been going on : — 
1820 70° 07-3 
1830 69 39'6 
1840 ... 69 11-9 
1850 68 45'9 
1860 68 19-9 
Lunar Radiation. — Professor Tyndall, by means of a thermo-electric pile, 
has been engaged in measuring the temperature of the moon’s rays. These 
observations were made from the roof of the Royal Institution, Albemarle-street. 
When the thermo-electric pile was directed off the moon, the needle oscillated 
between 10° and 20°, its mean position being 15°, When the pile was turned 
on the moon, the needle oscillated between 35° and 45°, the mean position 
being 40°. The following results were subsequently obtained : — • 
MEAN DEFLECTION. 
OFF THE MOON. 
15° 
27 
33 
ON THE MOON. 
40° 
40 
40 
“ These numbers all show cold, the deflection being such as would be pro- 
duced by the cooling of the face of the pile presented to the heavens ; and 
the result is, that the chilling teas in all cases greatest when the pile was directed 
towards the moon.'” These results are not in accordance with those obtained 
by Professor James Forbes some years since. 
HEAT. 
On the Propagation of Heat in Gases. — Dr. Tyndall has been for some time 
engaged in the investigation of this subject. The researches of Melloni will 
be remembered, but Dr. Tyndall has considerably extended the inquiry. Sul- 
phuric ether has been found to offer the most energetic resistance to the 
passage of radiant heat ; and the bi-sulphide of carbon to be least effective. 
Aqueous vapour also prevents the permeation of the dark heat rays. In a 
fine day in November, the aqueous vapour in the atmosphere produced fifteen 
times the absorption of the air itself. Variations in the quantity of vapour 
in the atmosphere would, therefore, necessarily produce corresponding varia- 
tions in climate. 
Magnus is also engaged in a similar inquiry, and has communicated a 
memoir on the subject to the Royal Academy at Berlin. As the investiga- 
tions are still in progress, we shall defer any consideration of the subject 
until the investigators have made further advances. 
