209 



in saline solutions, its properties are generally altered ; and he de- 

 scribes at length the phenomena thus presented in a solution of 

 sulphate of soda, which were peculiar and apparently perplexing, 

 but which he found to depend upon the presence of amalgam of so- 

 dium counteracting the effect of the negative pole, and exalting that 

 of the positive in proportion to its quantity, until it overcomes and 

 even reverses it. That sodium is actually present in these cases the 

 author shows by the following experiment : 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 be- 

 gan. 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 sufficiently powerful to decompose the 

 water. 



The author next proceeds to investigate more minutely the effects 

 of different metals in their contact and amalgamation with mercury, 

 employing solutions of the caustic alkalies for the conducting liquids, 

 which have the advantage of producing no currents 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, im- 

 parted to 100 grains of mercury the property of rotating violently 

 from the positive to the negative pole, when the circuit was com- 

 pleted in the liquid alone. The rotation was even sensible when the 

 quantity of potassium did not probably exceed a millionth part of the 

 whole mass. With sodium similar effects were observed ; and even 

 where the proportion of sodium to mercury was only as 1 to 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 motion, though present in considerable 

 proportion ; nor do bismuth, silver, nor gold. 



Mr. Herschel concludes this lecture with some general and the- 

 oretical observations and deductions, founded on his experimental 

 inquiries. These relate principally to the exceedingly minute pro- 

 portions of extraneous matter capable of communicating sensible me- 

 chanical motions, and properties of a definite character, to the body 

 they are mixed with. When we see energies so intense exerted by 

 the ordinary forms of matter, we may, says the author, reasonably 

 ask what evidence we have for the imponderability of any of the pow- 

 erful agents to which so large a part of the activity of material bodies 

 seems to be owing. 



Among the essential conditions of the phenomena, the author par- 

 ticularly adverts to the vast difference of conducting power between 

 the metallic bodies set in motion, and the liquid under which they 

 are immersed ; to the necessity of the perfect immiscibility of the con- 

 ducting fluids, so as to render the transition of one to the other quite 

 sudden; and to a certain chemical or electrical relation between 



VOL. II. P 



