[June 16 



Mr. T. Andrews. 



460 



arrangement .and methods of experimentation pursued are described 

 below, and the apparatus is delineated on fig. 1 and fig. 2. 



Two pieces were adjacently cut from a long finely polished iron 

 rod, so that the pieces might as near as practicable be of identical 

 chemical composition and molecular constitution. After being firmly 

 placed and adjusted as to equal length, &c, in the wooden supporting 

 frame W, they were immersed to an exactly equal depth in the solu- 

 tion contained in the U-tube, which latter was also rigidly supported 

 by a stand. In the duplex experiments made with apparatus fig. 2, 

 the U-tube was immersed in a large volume, four pints, of cold water 

 to ensure equal temperature conditions during experimentation for the 

 respective solutions in each limb, the cold water being maintained in 

 steady circulation around the tubes. The rods were connected in circuit 

 with a sensitive galvanometer, having a resistance of 521 ohms, and 

 of known calibration, the galvanometer being under constant tele- 

 scopic observation during the experiments, and the normal galvanic 

 action between the two bars previously observed in every experiment. 

 Considerable care was requisite to obtain this accurately, so as not 

 practically to interfere with the subsequent results seemingly due to 

 magnetic influences. A removable coil C, of stout silk-covered copper 

 wire (No. 16 gauge) mounted on a large wooden bobbin 6 inches long 

 enclosed the limb A of the U-tube, or when using apparatus fig. 2, 



