258 Proceedings of the Royal Society. 
and even reverses it. That sodium is actually present in these 
cases, the author shows by the following experiments : 
Having detached the negative wire, he touched the mercury now 
lying quiet in the liquid with a platinum or copper wire, and a 
violent action instantly began. The mercury rushed to the wire 
in a superficial current, and it gave off abundance of hydrogen, 
The sodium, wire, and liquid, forming a voltaic combination suffi- 
ciently powerful to decompose the water. 
The author next proceeded to investigate more minutely the 
effects of different metals in their contact and amaigamation with 
mercury, employing solutions of the caustic alkalies for the con- 
ducting liquids, which have the advantage of producing no cur- 
rents in pure mercury, so long as neither pole is in contact with it. 
In liquid potash a contact with the negative pole, of a single 
second’s continuance, imparted to 100 grains of mercury the pro- 
perty of rotating violently from the positive to the negative pole, 
when the circuit was completed in the liquid alone. The rotation 
was even forcible when the quantity of potassium did not probably 
exceed a millionth part of the whole mass. With sodium similar 
effects were observed, and even when the proportion of sodium to 
mercury was only as 1: 1.600.000, a feeble motion was sensible. 
The influence of barium, strontium, calcium, and. magnesium, 
and of zinc, lead, tin, and iron, is next described, the alloys of 
these metals being all possessed of the positive property. Copper, 
on the other hand, does not communicate it, though present in 
considerable proportion; nor do bismuth, silver, or gold. 
Mr. Herschel concludes this lecture with some general and 
theoretical observations and deductions, founded on his experi- 
mental inquiries. These relate principally to the exceedingly mi- 
nute proportions of extraneous matter, capable of communicating 
sensible mechanical motions and properties of a definite character 
to the body they are mixed with, When we see energies so in- 
tense exerted by the ordinary forms of matter, we may, says the 
author, reasonably ask, what evidence we have for the imponder- 
ability of any of the powerful agents, to which so large a part of 
the activity of material bodies seems to be owing? 
