NATURAL PHILOSOPHY. 177 



an ordinary gun, and is followed by the gases generated in the 

 gun, a very small part only escaping at the breech. Mr. llai'- 

 ding's theory of the action of his gun is this : That compression 

 of the air in the air-space behind the charge occupies an appre- 

 ciable time, during which the force of the explosion has been 

 communicated to the sliot. But it is obvious that his results, if 

 confirmed, will require a new examination of the action of pow- 

 der in close chambers, our present knowledge being insuflScient 

 for their adequate exjjlanation. In the meantime Mr. Harding 

 has made several hundred experiments, which are certainly inter- 

 esting and probably important. Of course, in such a gun, there 

 is no recoil; and hence the name he has given it. -r- Fojndar 

 Science Review, July, 1866. 



PRODUCTION OF ICE CYLINDERS BY PRESSURE THROUGH 



ORIFICES. 



The experiments of M. Fresca were made by acting on ice con- 

 tained in a cylinder 0.16 metre (about 6 inches) in diameter, with 

 the pressure necessar\' to drive it througli a central oi^ening in its 

 base 0.05 metre (nearly 2 inches in diameter). The plates, pre- 

 pared in Tyndall's method, in some cases colored at the joints, 

 acted like plates of lead or of porcelain paste, as before explained 

 by the author to the French Academj'. The surfaces of the 

 planes of division or joints, originally flat,were transformed into 

 tubes concentric and perfectly distinct from each other, thus indi- 

 cating the movement of each point of the mass during the change. 

 The ice cylinders were longitudinally furrowed, tlie furrows 

 appearing to proceed from fractures produced at the moment 

 when a portion of the cylindrical block leaves the orifice, and 

 when, consequently, it ceases to be subjected to pressure at the 

 outer extremity. The evenly bedded structure of the cylinder of 

 ice shows that the origin of these fractures is subsequent to the 

 formation of the cylinder. For a block of the dimensions above 

 given, the pressure required for the flow of the ice is 10,000 kilo- 

 grammes, one-fifth of that required for lead ; this pressure cor- 

 responds for the square centimetre to 126 kilogrammes, or to a 

 column of water 1,300 metres high. 



. The phenomena attending the formation of these ice cylinders 

 seem to throw light on the question of the movement of glaciers. 

 The relative displacement of the layers of ice in the process, the 

 change of form in the flat faces, the curved form of the beds at 

 the end of each partial tube, the large cavities formed toward 

 these ends, and the fissures or fractures at the moment of escape 

 fi'om the pressure, are so manj' points of resemblance to the 

 phenomena of glaciers. Though there is not the mass of material 

 forming moraines, the traces of coloring matter, deposited in 

 parallel threads and reunited toward the axis, complete the 

 analogy. — Les Mondes, Feb,, 1865. 



