1816.] during the Year 1815. 9 
they were circles passing through the pvints in which these primary- 
‘sets intersected each other. But I shall not attempt a particular 
description of the phenomena, because they could hardly be ren- 
dered intelligible without figures. 
V. ELECTRICITY. 
1. A set of observations on the electricity of the atmosphere 
during thunder-storms, rain, and snow, has been published by Dr. 
Schubler, of Hofwyl. He has given four examples, which are 
rendered easily intelligible by the graphical representation in Plate 
XLII. The changes in the state of the electricity take place so 
suddenly that it requires some dexterity to observe them and note 
them down. In the plate the horizontal line represents the time 
from minute to minute ; the perpendicular line denotes the degrees 
of the electrometer; the curve line within the scheme of course 
represents the position of the electrometer at the time specified in 
the horizontal line. 
The first scheme represents the variation of the electrometer 
during a thunder storm, which passed by at a distance. Warm 
weather had preceded April 11, 1806, on which the thunder storm 
took place; the day was cloudy, with a north-west wind, and a low 
barometer ; the thermometer at two o’clock stood at 57°; the height 
of the place where the observations were made was 1705 English 
feet above the level of the sea; the electricity of the atmosphere 
during the day had been weakly positive ; about six in the evening 
it began to rain, and the electricity of the rain was negative ; at 
seven the rain stopped; but the sky was covered with gloomy 
clouds, anda thunder storm commenced towards the south-west, 
with distant thunder and lightning ; the electricity of the air con- 
tinued still negative; but at each flash of lightning its negative 
state was suddenly diminished, the hand of the electrometer ap- 
proached 0, but returned almost immediately after the flash nearly 
to its original position. As the thunder storm approached nearer, 
the negative state of the atmosphere diminished. At 14 minutes 
past seven it became suddenly null, and even weakly positive, after 
a flash of lightning; but almost immediately after resumed its 
negative state. At 15 minutes after seven it became wholly positive; 
but the plate will show the changes which the electrometer under- 
went better than any description. The three remaining examples 
will be sufficiently understood from the figures. In the second of 
them the thunder was over head. 
2. It is generally known that when a pointed metallic body is 
attached to the prime conductor of an electrical machine, the 
electricity does not accumulate in the conductor, but makes its 
escape from the extremity of the pointed body in a visible stream of 
light. Professor Hildebrandt has lately made a comparative set of 
experiments in order to determine which metal, when placed in 
these circumstances, sends off the greatest visible stream of light. 
The metals were all made into cones with blunt summits, and they 
