and magnetic rotations. 
515 
Mean position of the needle, 
o 
249.O 
249- 2 5 
Lamp lighted. 
250.75 
2 56.25 
258.75 
256.25 
254-75 
260.25 
258.75 
262.25 
260.5 
261.25 
261.5 
268.5 
In this case, where a source of heat was revolving under a 
metal plate, the needle suspended above did not retrograde, 
but moved on in the same direction as the heat : the small 
comparative recession, at the sixth and seventh observation, 
not being of sufficient magnitude to be noticed, and it never 
having returned as far back as the point from which it 
started. 
From this experiment it appears, that, whatever may be 
the cause of these movements, it does not arise from any 
vortex produced by the moving part of the apparatus, nor is 
it owing to the passage of any air through the screens. 
In order to prove that no tremors arising from the moving 
power, and communicated through the solid parts of the ap- 
paratus, had produced these effects, the following experiment 
was made. 
