1 76 Mr. Herschel on certain motions produced in 
2 3. These effects, when first observed (not connectedly in 
regular succession, as here set down, but piece-meal), ap- 
peared exceedingly perplexing ; but the key to them was 
soon found. I observed that the effect of a contact of the 
negative pole was proportionally stronger in producing a 
positive radiation, as the mercury had been allowed to cir- 
culate longer before the contact was made, and, on more 
close examination, I found that the platina wire terminating 
the negative conductor of the pile, had got amalgamated 
with a little mercury, which, during the time the circuit was 
completed in the liquid, had become alloyed with sodium ; 
and, with the quantity of this metal judged to be present, the 
effect seemed always to be in proportion. I had no hesita- 
tion, therefore, in attributing all the new properties acquired 
by the mercury to the presence of sodium, and on introducing 
into a quantity of the pure metal a small quantity of an 
amalgam of this substance prepared for the purpose, I found 
my supposition verified ; a most violent negative rotation 
being immediately produced on completing the circuit, with- 
out allowing either wire to touch the mercury. 
24. The presence of this highly electro-positive metal there- 
fore counteracts the effect of the negative pole, and exalts 
that of the positive in a degree proportioned to its quantity, 
till at length it completely overcomes, and even reverses the 
former effect. As the quantity (in the foregoing experiment) 
diminished in the alloy by the oxidating action of the positive 
pole, the mercury, as we have seen, by degrees resumed its 
original properties. The only effect that may appear obscure, 
is the revulsion noticed in the direction of the currents when 
the last portion of oxide disappears. It is, in fact, a pretty com-* 
