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POPULAR SCIENCE REVIEW. 
Markings of Navicula rhomboides. By Dr. J. J. Woodward, U. S. 
Army. — Some Results of a Microscopical Study of the Belgian Plutonic 
Rocks. By A. Renard, S. J. — A New Microscopic Slide. By M. 
Ernest Yanden Broeck. — Measurements of Moller’s Diatomaceen- 
Probe-Platten. By Edward W. Morley, Hudson, Ohio, U. S. A. — On 
the Markings of the Body-scale of the English Gnat and the American 
Mosquito. By Dr. J. J. Woodward, U. S. Army. — Notes on Micro- 
photography. By Surgeon-Major Edward J. Gayer, H.M. Indian 
Army, now Professor of Surgery, Medical College, Calcutta. — On 
Renulia Sorbyana. By J. F. Blake, F.G.S. — Remarks on Frustulia 
Saxonica, Navicula rhomboides, and Navicula crassinervis. By Charles 
Stodder, U. S. A. — On the Measurement of the Angular Aperture of 
Object-glasses. By Jabez Hogg, Surgeon to the Royal Westminster 
Ophthalmic Hospital, F.R.M.S., &c. 
PHYSICS. 
The Waves as a Motive Tower. — Mr. B. Tower, who some time since 
described his method to an English audience, does not appear to have gone 
on in furtherance of his discovery. His machine consists in principle of a 
weight supported on a spring, so that it can oscillate on the spring through 
a considerable range in a vertical line. The scale of the spring, and conse- 
quently the natural period of oscillation of the weight, can be varied at 
will. When it is so adjusted that it synchronizes with the waves, the 
oscillations become very violent, and a large amount of power can be 
obtained from them. In practice, the springs consist of highly-compressed 
air pressing on the rims of hydro-pneumatic cylinders, and the arrangement 
is such that the vessel containing the compressed air forms the moving 
weight. At the meeting referred to Mr. Tower exhibited a design of a 
machine for working an auxiliary propeller of a sailing ship of 1,800 tons 
displacement. The moving weight in this case is 200 tons, and he showed 
by calculation that it would give about 30 horse-power in the long swell 
met with in the tropical calms, 260 horse-power in average ocean waves, 
and more than 600 horse-power in a heavy head sea. The space occupied 
by the machine compares favourably with a steam-engine of the same 
power. He also exhibited a model of the machine, which recently, in a 
moderate sea, had yielded power at the rate of 1^ horse* power per ton of 
moving weight. 
Experiments on the Periodic Waves of the Swiss Lakes. — At a recent 
meeting of the Physical Society of London (May 27), Professor Forel, of 
Morges, Switzerland, gave, in French, an account of some interesting expe- 
riments which he has recently made on the periodic waves which take place 
on the Swiss lakes, and are there called 11 Seiches.” It was long since 
observed that the waters of most of these lakes are subject to a more or less 
regular rise and fall, which at times have been found to be as much as one 
or two metres. M. Forel has studied this phenomenon in nine different 
lakes, and finds that it varies with the length and depth of the lake, and 
