342 The Mechamcal Action of Light. [July, 
were now washed out with oil of vitriol,* and the working 
was continued for an hour. 
The action of the incandescent spiral was now found to 
be energetically repellent, whether it was placed above or 
below the brass ball. The fingers exerted a repellent action, 
as did also a warm glass rod, a spirit-flame, and a piece of 
hot copper. 
In order to decide once for all whether these ations really 
were due to air-currents, a form of apparatus was fitted up 
which—whilst it would settle the question indisputably— 
would at the same time be likely to afford information of 
much interest. 
By chemical means I obtained in an apparatus a vacuum 
so nearly perfect that it would not carry a current froma 
Ruhmkorff’s coil when conneéted with platinum wires sealed 
into the tube. In such a vacuum the repulsion by heat was 
still found to be decided and energetic. 
* This can be effe@ed without interfering with the exhaustion. 
