52 Mr. J. Napier on the Dynamics of 



is the difference in time for Mars traversing the same celestial 

 arc at Otaheite and Wardhuus, an arc less than 0° 32'. 



" Several advantages are presented by this mode of ascertaining 

 parallax, if feasible. First, the inclination of the orbit of 

 Venus is 3° 23' 35"; whilst that of Mars is only 1° 51' 04", or 

 three-fifths of the other. Secondly, the observations can be made 

 at all oppositions with comparison stars, and the reductions to 

 the simple nodal passage easily performed. Thirdly, whilst a 

 great number of positions are necessary for the very rare transit 

 of an inferior planet, to obviate the possibility of cloudy weather 

 obscuring the solar disc, and where only travellers' instruments 

 can be used ; these observations may be conducted simultaneously 

 by professional astronomers, with firstrate instruments, at a few of 

 the principal observatories, e.g. Greenwich, the Cape, Paramatta, 

 Dorpat, and Madras. 



"S. M. Drach." 

 " November 30, 1843." 



P.S. I think I may fairly claim to having drawn attention to 

 this important method twenty years ago. As the travelling opinion 

 of a most eminent foreign observer was rather against the mea- 

 suring of a planet from a star with equal accuracy to the obser- 

 ving the critical moments of a transit over the sun's disc, I bowed 

 to the said decision,although it struck me as singular that the kind 

 of observations by which we fix the place of a new comet should 

 not be applicable for the above purpose. S. M. D. 



December 14, 1863. 



IX. On the Dynamics of the Galvanic Battery. 

 By James Napier, Esq. 



To William Francis, Esq. 



66 Miller Street, Glasgow, 

 Dear Sir, December 15, 1863. 



READING over the interesting paper of Professor William- 

 son " On the Dynamics of the Galvanic Battery," I observe 

 that he, in describing the electric current passing through a 

 solution of a salt, has assumed that the current of electricity, in 

 decomposing the salt, of necessity causes a mutual transfer, or 

 passage, of the elements of the salt to the different metallic elec- 

 trodes or battery plates : thus, in the decomposition of hydro- 

 chloric acid the chlorine passes to the zinc, and the hydrogen 

 to the copper. Referring to the diagram, page 460 of the De- 

 cember Number of this Magazine, he says, — 



" In the annexed diagram, Z represents the zinc plate, C repre- 

 sents the copper plate, and between them we have the chain of 



