i875-] 
M echanical A ction of Lig lit. 247 
suggested itself. If I can carry round heavy mirrors or plates 
of copper, I can carry round a magnet. Here, then (Fig. 9), 
is an instrument carrying a magnet, and outside is a smaller 
magnet, delicately balanced in a vertical position, having the 
south pole at the top and the north pole at the bottom. As 
the inside magnet comes round, the outside magnet, being 
delicately suspended on its centre, bows backwards and for- 
wards, and, making contadt at the bottom, carries an eledtric 
current from a battery to a Morse instrument. A ribbon of 
paper is drawn through the “ Morse ” by clockwork, and at 
each contadt—at each revolution of the radiometer— a record 
MAGNET 
is printed on the strip of paper by dots ; close together if the 
radiometer revolves quickly, farther apart if it goes slower. 
Here the inner magnet is too strong to allow the radiometer 
to start with a faint light without some initial impetus. 
Imagine the instrument to be on the top of a mountain 
away from everybody, and I wish to start it in the morning. 
Outside the bulb are a few coils of insulated copper wire, 
and by depressing the key for an instant I pass an eledtric 
current from the battery through them. The interior mag- 
net is immediately defledted from its north-south position, 
and the impetus thus gained enables the light to keep up the 
rotation. In a proper meteorological instrument I should 
