“ NEW FORCE ” OF M. J. THORE. 
465 
at the lower end. Round the needle is a ring of platinum wire, a , a, a , sealed into 
the glass and connected with outside terminals, c, c. A current of electricity from 
two Grove cells, turned on and off by a contact key, gives the power of making the 
wire red-hot when required. The fly consists of four thin vanes of clear mica, b, h, 
supported on light aluminium arms, and has in the centre a small glass cap, which 
rests on the needle-point. The vanes are inclined at an angle of 45° to the horizontal 
plane. They are in such a position that, when rotating, the centres of the vanes pass 
along the platinum ring and keep about 5 mm. distant from it. 
In describing the direction of rotation of the fly, I shall consider the observer’s eye 
to be on a level with the plane in which the fly rotates, and the direction recorded 
will be that taken by each vane as it passes in front. Assuming that the fly is 
rotating in the direction of the hands of a watch held face upwards on the top of the 
apparatus, each vane will be foreshortened, and, passing the observer, will have the 
appearance of /. The direction of rotation in this case will be considered as positive, 
i.e., as the direction followed by the fly, were molecular pressure or a molar wind to 
proceed from the platinum wire. 
In air of ordinary pressure (Bar. = 760 mm.), on igniting the platinum ring to 
redness by a current from two Grove cells, the vanes rotate in the positive direction, 
such as would be produced either by air-currents or by molecular pressure from the 
platinum ring. 
The following experiments were tried 
MDCCCLXXXVIJ.— 
3 , o 
