44 
Proceedings of Royal Society of Edinburgh . [sess. 
Demonstration of the Acoustic Turbine or Sound Mill 
of Alfred M. Mayer* and V. Dvorak, f By John G. 
M ‘Kendrick, M.D., Professor of Physiology in the Univer- 
sity of Glasgow. 
(Read February 17, 1896.) 
Dr M‘Kendrick showed this apparatus as made by Dr R. 
Koenig. It consists of four small and light cylindrical resonators, 
made of aluminium, tuned to Ut 4 = 512 vibs. p. sec., attached to 
the ends of four light bars forming a cross. The cross, carrying 
the resonators, is balanced on a fine pivot placed vertically. When 
the fork is sounded (by an electro-magnet between the limbs) the 
cross carrying the four resonators begins to rotate. The motion 
arises from the greater pressure at the node at the closed end in the 
interior of the resonator nearest the source of sound than on the 
outer surface of this end. If the mouth of the cylinder is directed 
towards the source of sound, the resonator is repelled by the greater 
pressure within. The next resonator is slightly attracted, but it is 
brought within the sphere of greater pressure mainly by the inertia 
of the first resonator, and so on. J 
* Invented by A. M. Mayer in January 1876, and shown on May 22nd, 
1876, to the New York Academy of Sciences. 
f Invented independently by V. Dvorak, and described by him in Annalcn 
der PhysiJc und Chemie , Band III., No. 3, dated 10th November 1877. 
+ See also American Journal of Science, third series, vol. xvi. p. 22. 
