430 The Philosophical Instruments in the Paris Exhibition. 



worthy instrument, has, in the hands principally of Naudet, of 

 Paris, been still further improved, and especially those intended 

 for pocket use. Bourdon's metallic barometers, composed of 

 coiled tubes exhausted of air, and hermetically sealed, have 

 also been considerably improved, principally by Richard, of 

 Paris, who states that they now require no correction. 



A great variety of excellent thermometers were exhibited, 

 principally by foreign makers. No important improvement 

 was, however, apparent. . Those made by Reverend, of Paris, 

 are remarkable for their clear and well-cut graduations. 

 Mr. Bache, of the United States, exhibited a deep-sea ther- 

 mometer of novel construction, for registering the temperature 

 by the action of metal bars. M. Breguet's metallic ther- 

 mometer has been further improved, so as to render it more 

 sensitive. This instrument has been lately used by Mr. Wheat- 

 stone, in connection with his invention for ascertaining the 

 temperature at distant places by telegraphy. By means of 

 magnets and connecting wires, a Breguet thermometer, placed 

 on the summit of Mont Blanc, can be read off at Chamouni, 

 or the temperature at great depths in the earth or ocean 

 ascertained in the same manner at any moment. 



Electricity, and especially electro-magnetism, was largely 

 illustrated. The apparently inexhaustible applications of this 

 mysterious force are continually taxing the inventive power of 

 man. The grand desideratum, however, of obtaining a motive 

 force which shall supersede that of steam has not yet been 

 discovered, the few machines of this nature in the Exhibition 

 being at once weak and costly. The great mechanical difficulty 

 which prevents the application of electro-magnetism as motive 

 power in prime movers is the short distance through which the 

 action of magnetism extends. This has been sought to be 

 overcome by calling into action, seriatim, a number of electro- 

 magnets. It is possible by this means to work a crank of one 

 or two inches in length with sufficient power to turn a small 

 lathe ; but it admits of easy demonstration that an electrical 

 machine, with zinc for its fuel and acid to burn it, cannot be 

 made to rival steam-engines. 



Mr. W. Ladd exhibited a very ingenious and energetic 

 electro-magnetic machine, embracing the new principle of 

 augmenting indefinitely the power of an electro-magnet by 

 currents produced by itself. The apparatus can be employed 

 for lighthouses, or other purposes. It is driven by a one-horao 

 power steam-engine, by which force effects are produced quite 

 equal to a fifty Grove's battery.* 



Very beautiful illustrations were exhibited of the application 



* Mr. Saxby ha9 lately discovered that by passing electro-magnetic currents 

 through maBses of iron, internal flaws in the iron can bo unfailingly detected. 



