in changing the Dimensions of Iron. 351 



wires, each 110 yards long and 2V °f au i ncn i n diameter, 

 were bound together by tape so as to form a good and at the 

 same time very flexible conductor. The bundle of wires thus 

 formed was coiled upon a glass tube 40 inches long and 1J inch 

 in diameter. One end of the tube was hermetically sealed; and 

 the other end was furnished with a glass stopper, which was itself 

 perforated so as to admit of the insertion of a capillary tube. In 

 making the experiments, a bar of annealed iron, 1 yard long and 

 \ an inch square, was placed in the tube, which was then filled 

 up with water. The stopper was then adjusted, and the capil- 

 lary tube inserted so as to force the water to a convenient height 

 within it. 



" The bulk of the iron was about 4,500,000 times the capacity 

 of each division of the graduated tube; consequently a very 

 minute expansion of the former would have produced a very 

 perceptible motion of the water in the capillary tube ; but, on 

 connecting the coil with a DanielPs battery of five or six cells 

 (a voltaic apparatus quite adequate to saturate the iron), no per- 

 ceptible effect whatever was produced either in making or break- 

 ing contact with the battery, whether the water was stationary 

 in the stem, or gradually rising or falling from a change of 

 temperature. Now, had the usual increase of length been un- 

 accompanied by a corresponding diminution of the diameter of 

 the bar, the water would have been forced through twenty divi- 

 sions of the capillary tube every time that contact was made with 

 the battery. 



" Having thus ascertained that the bulk of the bar was inva- 

 riable, I proceeded to repeat my first experiments with a more 

 delicate apparatus, in order, by a more careful investigation of 

 the laws of the increment of length, to ascend to the probable 

 cause of the phenomenon. 



" A coiled glass tube, similar to that already described, was 

 fixed vertically in a wooden frame. Its length was such that 

 when a bar 1 yard long was introduced so as to rest on the 

 sealed end, each extremity of the bar was a full inch within the 

 corresponding extremity of the coil. The apparatus for obser- 

 ving the increment of length consisted of two levers of the first 

 order, and a powerful microscope situated at the extremity of the 

 second lever. These levers were furnished with brass knife-edges 

 resting upon glass. The connexion between the free extremity 

 of the bar of iron and the first lever, and that between the two 

 levers, was established by means of exceedingly fine platinum 

 wires. 



" The first lever multiplied the motion of the extremity of the 

 bar 7'8 times; the second multiplied the motion of the first 8 

 times ; and the microscope was furnished with a micrometer di- 



