Proceedings of the British Association. 339 



tage of a temperature nearly equal throughout the year. Sec- 

 ondly, the instruments are of unusually large dimensions, and are 

 in all respects sufficient for the most delicate investigations. — 

 Dr. L. gave also a general statement of the system of meteoro- 

 logical observations carried on in Bavaria ; the results of which 

 appear in the annual publications of the Royal Observatory of 

 Munich. 



Prof. Jacobi, of St. Petersburgh, gave a historical sketch of the 

 laws which regulate the action of Electro-magnetic machines. 

 After recounting the theoretical researches carried on by himself 

 with the assistance of M. Lenz, he adds, " Unfortunately, I can- 

 not here give the details either of the experiments which I have 

 made upon a very large scale, or of the machines and apparatus 

 of various kinds which I have constructed. The necessity of 

 multiplying the facts or tangible results, — a necessity the more 

 ur'gent, because the practical applications of this force increased 

 so very rapidly, — this necessity I say, has not allowed me time 

 to digest and arrange them. I will, however, particularly notice 

 the satisfactory results of the experiments made last year with a 

 boat of 28 feet long, and 7^ feet wide, drawing 2f feet of water, 

 and carrying 14 persons, which was propelled upon the Neva at 

 the rate of about 3 English miles in the hour. The machine, 

 which occupied very little space, was set in motion by a battery 

 of 64 pairs of platinum plates, each having 36 square inches of 

 surface, and charged according to the plan of Mr. Grove, with 

 nitric and diluted sulphuric acid. Although these results may 

 perhaps not satisfy the exaggerated expectations of some per- 

 sons, it is to be remembered that in the first year, viz. in 1838, 

 this boat being put in motion by the same machine, and employ- 

 ing 320 pairs of plates, each of 36 square inches, and charged 

 with sulphate of copper, only half this velocity was obtained. 

 This enormous battery occupied considerable space, and the ma- 

 nipulation and management of it were very troublesome. The 

 judicious changes made in the distribution of the rods, in the 

 construction of the commutator, and lastly in the principles of 

 the voltaic battery, have led to the successful result of the fol- 

 lowing year, 1839. We have gone thus on the Neva, more than 

 once, and during the whole day, partly with and partly against 

 the stream, with a party of 12 or 14 persons, and with a velocity 

 not much less than that of the first-invented steamboat. I be- 



