738 Proceedings of the lloyal Society of Edinburgh. 
might usefully intensify them. I therefore had copper plates 
soldered perpendicularly to the revolving disc, so as to increase 
instead of diminishing the virtual thickness of the edges of the 
apertures. The result was very striking. Such a siren gives a 
sound whose intensity is not sensibly increased by a powerful blast 
from an organ bellows. It produces strong currents of air through 
the holes in the fixed disc, whose direction in general depends upon 
the direction in which the rotating disc is made to revolve; and 
especially does so when the copper plates are inclined to the surface 
of that disc. When the discs are both furnished with these plates, 
turned in opposite directions, the result is still more striking. 
Various other modifications have occurred to me, and are now 
under trial, especially one for producing currents alternately in 
opposite directions through the holes. 
By bringing up a flat plate towards the instrument, the quality 
of the sound is altered in a remarkable manner, and to such an 
extent that it seems well adapted for rapid Morse-signalling. As 
this instrument requires no work to be spent except in turning it, 
a very large number may be kept continuously at work at once by the 
same expenditure of power as is required for the intermittent roaring 
of a single fog-siren. 
The following Gentlemen were duly elected Fellows of the 
Society : — 
James R. Stewart, M.A. Oxon., 10 Minto Street. 
John Archibald Campbell, M.D., Garland’s Asylum, Carlisle. 
