240 Intelligence and Miscellaneous Articles, 



pressure required for the flow of the ice is 10,000 kilogs., while for 

 lead it is 50,000 kilogs. These pressures correspond, for the square 

 centimetre, to 126 and 630 kilogs. This pressure of 126 kilogs. 

 corresponds to a column of water 1300 metres in height. It is evi- 

 dent that if the orifice were smaller in proportion to the diameter 

 of the mass under pressure, the force requisite would be notably 

 less. 



M. Fresca observes that the circumstances attending the forma- 

 tion of these jets of ice appear to throw light on the controverted 

 question as to the movement of glaciers. The relative displacement 

 of the layers of ice in the process, the change of form in the faces 

 originally flat, the curved form of the layers at the extremity of each 

 partial tube, the large cavities formed toward these extremities, and 

 even the fissures or fractures at the moment of escape from the pres- 

 sure, are so many points of resemblance to the phenomena of glaciers. 

 There is not the mass of material constituting moraines; but the traces 

 of colouring-matter which are deposited in parallel threads, and 

 which are reunited towards the axis, complete to a degree the 

 analogy. 



Tyndall had before shown that ice could be moulded to any shape 

 by pressure in a mould. M. Fresca observes that his trials prove, 

 in addition, that it may be pushed into a thread, in accordance with 

 the geometrical law of this kind of flow. The facts help to bring 

 the explanations of Tyndall and Forbes into accord, since they indi- 

 cate that the viscosity, more or less great, of the material does not 

 necessarily play any important part in the phenomenon. They ex- 

 hibit the material conditions of the flow : and the transparency of the 

 jet after its escape from the orifice shows besides, that, under a com- 

 paratively feeble pressure, ice may be changed in form without ceasing 

 to be glassy in texture or aspect. — Les Mondes, February 23 (Silli- 

 man's American Journal for July 1865. 



NOTE ON THE REFLEXION OF SOUND. BY M. VIONNOIS. 



Being on the manceuvring-ground at Nancy, in an extensive plain, 

 the echoes of the troops firing were very distinctly heard ; yet in- 

 stead of being sharp, they were slightly confused and prolonged. The 

 trees of an English garden, separated from the manceuvring-field, 

 could alone have produced this phenomenon ; the leaves were thus 

 reflecting surfaces. This fact enables us to understand how the 

 explosion of the electric spark may be reflected by the vesicular 

 vapour of clouds, and the sound be softened and considerably pro- 

 longed, owing to the inequality of the distances and of the successive 

 reflexions. — Comptes Rendus, February 27, 1865. 



