208 



Nautical Almanac ; while Mr. Ivory makes it 34' 17 "'5. Again, for 

 the altitude 5 44' 21", we obtain 8' 49"'5 for the refraction; while 

 the Nautical Almanac gives us 8' 53", and Mr. Ivory's table 8' 49"'6. 

 The author, however, observes that there is no reason for proceeding 

 to compute a new table by this formula, since the method employed 

 for that in the Nautical Almanac is in all common cases more com- 

 pendious ; and even if it were desired to represent Mr. Ivory's table 

 by the approximation there employed, we might obtain the same re- 

 sults, with an error scarcely exceeding a single second, from an 

 equation of the same form. 



The Bakerian Lecture. On certain Motions produced in Fluid Con- 

 ductors when transmitting the Electric Current. By J. F. W. Her- 

 schel, Esq. F.R.S. Read February 12, 1824. [Phil. Trans. 

 1824, p. 162.] 



In the first paragraphs of this lecture, Mr. Herschel describes the 

 phenomena that result on placing a portion of mercury covered with 

 sulphuric acid between the voltaic poles immersed on opposite sides 

 of the globule of metal, but in contact with the acid only. They 

 consist in active motion of those particles of the acid in contact with 

 the mercury, while the superficial molecules of the metal continually 

 radiate from the point nearest the negative pole, and darting to the 

 positive pole return along the axis. The author particularly notices 

 several singular appearances resulting from this current, and shows 

 them to be independent of any electro-magnetic vortices, to which, 

 at first sight, they present considerable analogy. They are incom- 

 parably more forcible, in proportion to the electric powers used, than 

 the motions produced by the action of magnets ; hence, they furnish 

 an extremely sensible test of the development of feeble Voltaic pow- 

 ers not easily rendered sensible by other means. 



The author next describes the appearances observed in cases where 

 other liquids and metals are used, and adverts to the influence of 

 several causes upon the uniformity of the results. Among these, im- 

 purity in the mercury is especially noticed, which should not only be 

 carefully distilled, but also well washed with dilute nitric acid. Mer- 

 cury thus prepared, and placed in the current as before, exhibits phe- 

 nomena varying with the nature of the liquid ; generally speaking, 

 currents are produced radiating from the point nearest the negative 

 pole, which are most violent in acids, and less in saline solutions, in 

 proportion as the electro-positive energy of the base is greater. In 

 many liquids a counter- current from the positive pole is observed ; 

 but if either pole be brought in contact with the mercury, no cur- 

 rents are observed from the point of contact, btit strong ones are 

 perceived to radiate from the other. If the negative pole touch it, it 

 amalgamates with the mercury, which remains bright ; if the positive, 

 the mercury rapidly oxidizes ; and in both cases currents are pro- 

 duced. 



Mr. Herschel proceeds to observe, that when mercury is electrized 



