Results obtained with the Gymnotus Current. 363 



1764. By this test I compared the middle part of the fish 

 with other portions before and behind it, and found that the 

 conductor A, which being applied to the middle was negative 

 to the conductor B applied to the anterior parts, was, on the 

 contrary, positive to it when B was applied to places near the 

 tail. So that within certain limits the condition of the fish 

 externally at the time of the shock appears to be such, that 

 any given part is negative to other parts anterior to it, and 

 positive to such as are behind it. 



1765. Evolution of heat. Using a Harris's thermo-electro- 

 meter belonging to Mr. Gassiot, we thought we were able in 

 one case, namely, that when the deflection of the galvanome- 

 ter was 40° (1761.), to observe a feeble elevation of tempera- 

 ture. I was not observing the instrument myself, and one of 

 those who at first believed they saw the effect now doubts the 

 result*. 



1766. Spark. The electric spark was obtained thus. A 

 good magneto-electric coil, with a core of soft iron wire, had 

 one extremity made fast to the end of one of the saddle col- 

 lectors (1758.), and the other fixed to a new steel file; another 

 file was made fast to the end of the other collector. One per- 

 son then rubbed the point of one of these files over the face 

 of the other, whilst another person put the collectors over the 

 fish, and endeavoured to excite it to action. By the friction 

 of the files contact was made and broken very frequently ; 

 and the object was to catch the moment of the current through 

 the wire and helix, and by breaking contact during the cur- 

 rent to make the electricity sensible as a spark. 



1767. The spark was obtained four times, and nearly all 

 who were present saw it. That it was not due to the mere 

 attrition of the two piles was shown by its not occurring 

 when the files were rubbed together, independently of the 

 animal. Since then I have substituted for the lower file a 

 revolving steel plate, cut file-fashion on its face, and for the 

 upper file wires of iron, copper and silver, with all of which 

 the spark was obtained f . 



1768. Such were the general electric phaenomena obtained 

 from this Gymnotus whilst living and active in its native ele- 

 ment. On several occasions many of them were obtained 

 together; thus a magnet was made, the galvanometer de- 



* In more recent experiments of the same kind we could not obtain 

 the effect. 



t At a later meeting, at which attempts were made to cause the attrac- 

 tion of gold leaves, the spark was obtained directly between fixed surfaces, 

 the inductive coil (1766.) being removed, and only short wires (by com- 

 parison) employed. 



