is constantly losing heat by radiation, and dif- 
ferent soils have their temperatures differently 
diminished by this cause. 
When a piece of sealing-wax is rubbed by a 
woollen cloth, it gains the power of attracting light 
bodies, such as feathers or ashes. In this state it is 
said to be electrical ; and if a metallic cylinder, 
placed upon a rod of glass, is brought in contact 
with the sealing-wax, it likewise gains the momen- 
tary power of attracting light bodies, so that 
electricity, like heat, is communicable. When two 
light bodies receive the same electrical influence, 
or are electrified by the same body, they repel 
each other. When one of them is acted on by 
sealing-wax, and the other by glass that has been 
rubbed by woollen, they attract each other ; hence 
it is said that bodies similarly electrified repel 
each other, and bodies dissimilarly electrified at- 
tract each other : and the electricity of glass is 
called vitreous or positive electricity, and that of 
sealing-wax resinous or negative electricity. 
When, of two bodies made to rub each other, one 
is found positively electrified, the other is always 
found negatively electrified, and, as in the com- 
mon electrical machine, these states are capable of 
being communicated to metals placed upon rods or 
pillars of glass. Electricity is produced likewise 
by the contact of bodies ; thus a piece of zinc and 
of silver give a slight electrical shock when they 
are made to touch each other, and to touch the 
tongue ; and when a number of plates of copper 
and zinc, 100 for instance, are arranged in a pile 
with cloths moistened in salt and water, in the 
d 3 
