66 



MECHANICAL POWERS. 



if a plate of silver, as a halfcrown, be placed upon the 

 tongue, and a plate of zinc, of about the same size, be 

 placed under the tongue, on bringing the edges of the 

 metals into contact, a sharp and singular taste will be 

 experienced. If the zinc be placed beneath the tongue, 

 and the silver between the lips and gums, near the eye- 

 tooth, and the two metals be brought into contact, a 

 distinct flash of light will be visible.* 



Various facts in common life are explained by Galvan- 

 ism. The superior flavour of porter when drunk from a 

 pewter pot has been attributed to this action, the pewter 

 being a mixture of two different metals ; as also snuff 

 having a different flavour when taken from a tin box in 

 which part of the iron has become exposed, from that 

 which it has when in contact with tin alone. 



Electricity and Voltaism are probably the most inte- 

 resting of all the sciences, from the numerous and 

 splendid experiments which may be performed by their 

 means, as also from their intimate connexion with the 

 various operations of nature ; t yet* notwithstanding 

 the most unwearied investigations of men of the high- 

 est science and talent, much yet remains undiscovered 

 and unknown. 



MECHANICAL POWERS. 



Origin and advantage of Mechanical Powers The different kinds of Levers- 

 Wheel and Axle Pulley Inclined Plane Wedge and Screw, each explained, 

 with the principle of its action Examples, &c. &c. 



THE Mechanical Powers are engines used for raising 

 great weights, moving heavy bodies, &c., without the aid 



* This is caused by the irritation of the optic nerve, in a manner 

 similar to that produced by a blow on the eye. 



f At the meeting of the British Association, held a few years since 

 at Bristol, Mr. Crosse, of Broomfield, Somerset, stated that he had 

 kept the Voltaic power in force for twelve months by water alone. He 

 had obtained water from a crystallized cave, and by the action of the 

 Voltaic Battery he had produced from that water numerous rhomboidal 

 crystals resembling those of the cave. He had also obtained carbon- 

 ates of copper, phosphate of soda, and 20 or 30 other specimens ; and 

 imagined that diamond itself might be produced by Voltaic action. 



