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 ahistorical 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 
urgent, 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 74 feet wide, drawing 23 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 
nitrie 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 Jastly 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 
Hot much less than that of the first-invented steamboat. I be- 
* 
