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POPULAR SCIENCE REVIEW. 
On the Flow of Solid Bodies. — M. Tresca has communicated a remarkable 
paper to the French Academy of Sciences under the above title, containing 
the results of researches on the deformation of solid bodies under pressure, 
which M. Tresca seeks to explain by laws analogous to those of the flow of 
liquids. The experiments were made on blocks consisting of thin sheets of 
lead, and these were punched through by a cylindrical steel punch, distorted 
by compression in a direction perpendicular to the layers ; and, lastly, forced 
from a cylindrical chamber through an orifice. In all cases the molecules of 
the solid were found to change their places, flowing in the direction of least- 
resistance in a manner analogous to fluid flow. In the case of the lead forced 
through an orifice, a contracted vein was formed, a very singular result. M. 
Tresca has subjected these experiments to mathematical analysis, with a view 
of finding a basis for a new theory of the resistance of materials. Some 
account of these experiments will be found in “ Engineering ” for March 16. 
Negative Slip. — At the Institute of Naval Architects Mr. E. J. Reed read 
a very interesting paper on the Negative Slip of screw steamers, as it is called, 
or the phenomenon of a ship advancing in the water at a greater rate 
than that due to the pitch and number of revolutions of the screw. After 
discussing the various theories which have been proposed to account for this 
apparently paradoxical result, and rejecting them as insufficient, Mr. Reed 
stated that, in his belief, the cause of negative slip would be found in the 
elasticity of the fluid combined with the stream or current following in the 
vessel’s wake. 
The Non-recoil Gun. — Mr. Gr. P. Harding has recently proposed and ex- 
perimented upon a gun on a principle so novel that, if his expectations 
are fulfilled, the manufacture of fire-arms will be revolutionized. His gun 
is, in fact, a simple cylindrical tube without any breech. The shot is 
placed at the centre, the charge behind it confined by a wad, and a second 
wad is introduced at such a distance as to leave an air-space behind the 
charge. Now the extraordinary fact developed by Mr. Harding’s experiments 
is this : — That, although the gun is equally open in both directions, almost the 
whole force of the explosion takes effect on the shot, which attains the same 
velocity as if fired from an ordinary gun, and is followed by the gases gene- 
rated in the gun, a very small part only escaping at the breech. Mr. Harding’s 
theory of the action of his gun appears to be this : — That compression of the 
air in the air-space behind the charge occupies an appreciable time, during 
which the force of the explosion has been communicated to the shot ; but it 
is obvious that Mr. Harding’s results, if confirmed, will require a new exa- 
mination of the action of powder in close chambers, our present knowledge 
being insufficient for their adequate explanation. In the mean time Mr. 
Harding has made several hundred experiments, which are certainly interest- 
ing and probably important. Of course, in such a gun as Mr. Harding’s 
there is no recoil, and hence the name he has given to it. 
