380 OBSERVATIONS AND EXPERIMENTS 



those who form an exaggerated idea of what can be determined 

 with a few live Malapterurus in the laboratory, and to whom my 

 results may seem too meagre. 



Add to this, that the methods of investigation had to be almost 

 entirely contrived. I will relate first, how I was provided in this 

 respect. 



I. Observation of the shock of the Malapterurus with reflecting 

 magnet, scale, and telescope. 



By the term experimental circuit, will henceforth be understood 

 the system of conduction by which the discharge of the fish is led 

 off, in order to examine any of its effects, whether the circuit be 

 interrupted or not. A Wiedemann's galvanometer was usually 

 introduced into it in order to measure the discharge. 



In all earlier experiments with Malapterurus, ordinary multi- 

 pliers with astatic pairs of needles had been used. Apart from the 

 fact that they are ill-fitted for measurements, such an instrument is 

 here especially unserviceable. At times I found that the needles 

 are caught by the shock when they are at a great angle to the 

 direction of the coil, by which they are either rendered, no longer 

 astatic, or may be even almost entirely demagnetised or reversed. 

 Observation of the deflections with mirror, scale, and telescope could 

 never be more advantageously made than here, and Herr Eckhard 

 and I introduced them simultaneously, he at Trieste in experiments 

 on the Torpedo, and I here in those on the Malapterurus. When a 

 Wiedemann's galvanometer was used, and one of the thermo- 

 bobbins containing 53 turns of wire was allowed to act at a 

 distance of 25~75 nim. on a heavy reflecting magnet not rendered 

 astatic, I obtained measured deflections from the discharge of the 

 Malapterurus, without risk of a disturbing effect on its magnetism. 

 The aperiodic magnet would have been of great advantage in these 

 observations, but at that time I had not got so far. 



2. The leadlng-off cover. 



The shock of the fish in the experimental circuit is weakened by 

 derivation, in proportion as the mass of water in which the fish is 

 contained is greater. The action of the fish is also physiologically 

 violent as the quantity of water is less. Thus they were less able 

 to kill other fish in the trough than in the tubs. That they were 

 able to do so in the Edinburgh basins, which were certainly not 



