255 



which require a great number of pairs. He had, in previous experi- 

 ments, found that fresh phosphuret of calcium was a conductor for 

 350 pairs of 7 X 3, but not for 100 pairs of 71 X 14. 



The deflagration of an iron wire by contact with mercury, took 

 place with phenomena which were never before witnessed by any of 

 the spectators. At first the mercury was deflagrated with an intense 

 silvery white light, after which there arose a vertical shower of red 

 sparks, caused by the combustion of the iron. Lastly, a globule 

 having accumulated at the end of the wire after a momentary stop- 

 page of the reaction, an explosion took place, by which fragments of 

 the globule, together with portions of the mercury, were projected to 

 a great distance. 



It would seem, said Dr. Hare, as if a globule of peroxide of iron, 

 having formed at the end of the wire, caused a temporary arrestation 

 of the voltaic current; but that the apparatus, gaining energy in con- 

 sequence of a transient repose, was unable to break through the glo- 

 bule so as to disperse its particles with violence. 



Mr. Walker made some remarks on the tornado, of limited 

 extent, which visited Philadelphia on the 13th instant. 



Mr. Walker's own observations, and those of several intelligent in- 

 dividuals, on different sides of the central path, led him to the conclu- 

 sion, that the currents from without the borders of the tornado were 

 directed, in every instance, towards its centre. This was manifest 

 from the motion of the clouds, in the different strata of the atmos- 

 phere. The theory of the central tendency of the currents in tor- 

 nadoes, usually ascribed to Mr. Espy, was, Mr. Walker remarked, of 

 older date, having been advanced by Franklin in the middle of 

 the last century. The whirl, on which so much stress is laid by Mr. 

 Redfield and Colonel Reid, was distinctly seen in the lower current, 

 where the condensed vapour, resembling spent steam, moved round 

 in a spiral, making several turns downwards, each of smaller dimen- 

 sions than the preceding, and resembling the motion of water in a 

 common whirlpool. This circumstance seemed, to Mr. Walker, 

 somewhat contradictory to part of Mr. Redfield's theory, that of the 

 gradual enlargement of the periphery of the whirl, whereas the mo- 

 tion in the present instance was in a spiral tending inwards. 



Mr. Lea confirmed, from his own observations, the central 



