722 Experiments on the communication of [Sept. 



The cross lines above the numbers exhibit the wires led from each 

 half mile of conductor. Thus by cutting through 1. 1. the next num- 

 bers to right and left became the conductors or nearest electrodes, 

 and the length of the circuit thus rose from one to three miles ; cutting 

 2. 2. will make 3. 3. the electrodes, and increase the circuit to five 

 miles, and so on, each section added a mile to the circuit at either 

 side. 



The wires employed were of iron (annealed), diameter one-twelfth 

 of an inch. It is almost needless to observe that iron was used not 

 from choice but necessity. A sufficient quantity of copper wire was 

 not procurable in Calcutta, no draw-bench was ready to manufacture 

 the necessary supply, moreover the rainy season was fast approaching 

 when such experiments could scarcely be attempted, constant exposure 

 in the open air being essentially requisite to success. The expense 

 again of copper would have amounted to much more than a private 

 individual could afford. 



With iron wire however I considered that the results would be still 

 of much practical value. Being the worst of the metallic conductors 

 of electricity, it seemed a reasonable inference that whatever might be 

 found practicable with iron, would a fortiori be so with the copper, 

 or best conductor. 



On the completion of the line the following instruments were tried. 



1st. An electro-magnet of soft iron, 1^ inch in diameter, poles 

 1 inch apart, length from centre to poles 12 inches, weight 14 lbs. 

 surrounded by one hundred yards of insulated copper wire, the twelfth 

 of an inch in diameter. This electro-magnet, when excited by the 

 voltaic battery used in the subsequent experiments, with conductors 

 seven feet in length, supported 2401bs. 



2nd. An electro-magnet of very small size, constructed by Watkins, 

 of London, capable of supporting 301bs. with the battery now referred 

 to, and with the same length of conductors. 



3rd. An astatic galvanometer by Watkins and Hill, already refer- 

 red to. 



4th. An electro-magnetic induction machine, also by Watkins, of 

 which a brief description is desirable. 



This instrument consists of a coil of thick wires insulated by silk, 

 and wound spirally round a wooden cylinder having a hollow axis one 

 inch in diameter. The ends of this coil are connected with metallic 

 screws, so that they can be joined to the poles of a voltaic battery. 



