The nearly vertical vanes is balanced by the convection currents.
When the rays of the sun or a candle, or dark radiation from a warm body, are incident on the vanes, the dark side of each vane is repelled more than the bright side, and thus the vanes are set into rotation with accelerated speed, which becomes uniform when the forces produced by the radiation are balanced by the friction of the pivot and of the residual air in the globe.
Centrifugal pumps, constructed with several stages or sets of vanes, and suitable for high lifts, have been introduced for mine service.
The best-known of Joule's experiments was that in which a brass paddle consisting of eight arms rotated in a cylindrical vessel of water containing four fixed vanes, which allowed the passage of the arms of the paddle but prevented the water from rotating as a whole.
Each channel is divided into a series of pockets by equally spaced vanes inclined at 45°.