L. MECHANICS AND ENGINEERING. 481 



charges, placed simply upon the surface of submerged soft 

 chalk rock, would break up the latter so as to facilitate its 

 rapid removal by dredging, the rock being completely disin- 

 tegrated, or pounded into a plastic mass like clay. Com- 

 paring the effects of dynamite containing Id per cent.. of ni- 

 tro-glycerine with those of gun-cotton, the two materials 

 appear to be practically on an equality, weight for weight, 

 but the results furnished by either of them are accepted as 

 being about six times those produced by gunpowder. The 

 most prominent advantage of dynamite over gun-cotton is 

 that it may be used in a damp hole without fear of its miss- 

 ing fire; while, on the other hand, compressed gun-cotton 

 possesses the advantage that it is not in any way injurious 

 to handle, is not at all affected in its explosiveness by cold, 

 and may be preserved for any length of time without dete- 

 rioration in its damp and unignitable state. The vapors 

 evolved from the explosion of either of these are decidedly 

 more objectionable than gunpowder smoke. Abel on Explo- 

 sive Agents. 



AN INGENIOUS AND NEW MOTOR. 



According to the laws of the mechanical theory of heat, 

 mechanical work can be produced by the employment of 

 any differences whatever of heat ; and a very simple device 

 has been invented by Bernardi, which is curious, if not of 

 industrial value. Two glass globes are united by thin me- 

 tallic arms to a central drum, the arms being bent at right 

 angles when they enter the globes. The globes are partly 

 filled with ether. An axle passes through the central drum 

 in such a way that as it revolves, carrying the arm and the 

 globes with it, the globes successively dip into a basin of 

 cold water. Each globe is covered by a very fine network, 

 which, becoming wet in that part of its revolution that carries 

 it below, is subsequently, during the greater part of its rev- 

 olution, exposed to the air. Evaporation of the water over 

 the exterior of the network, and the consequent cooling of 

 the globe, causes a slight condensation of ether in its interior, 

 more of which is supplied from the opposite globe then being 

 immersed in water, the upper or exposed globe becomes the 

 heavier, and by its tendency to sink keeps the axle in con- 

 tinued but slow rotation, which does not cease so long as 



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