Hydrography, and the Art ()f Navigation, 81 



to be a place very well adapted for the purpose. The observa- 

 tion may likewise be repeated on the Tacx)ra, if the expedition 

 stop for a few days at Arica. 



LUMINOUS METEORS. 



On Lightning, — M. Fusinieri has been lately studying the 

 effects of lightning under an entirely new point of view. 



According to this philosopher, the electrical sparks issuing 

 from ordinary machines, which we see as they traverse the air, 

 contain brass in a state of fusion and incandescent molecules of 

 zinc, when they emanate from a brass conductor ; if the sparks 

 issue from a ball of silver they contain impalpable particles of 

 that metal. In the same way, a globe of gold gives rjse to sparks, 

 which contain, during their passage through the air, melted gold, 

 &c., &c. 



In the centre of all these sparks the molecules are melted 

 only; but in the circumference, the metallic particles undergo a 

 greater or less degree of combustion, in consequence of their con- 

 tact with the oxygen of the atmosphere. 



When a spark issuing from a globe of gold traverses a silver 

 plate, even of considerable thickness, there is seen on the two 

 surfaces of the plate, at the point where the electric spark en- 

 tered and emerged, a circular layer of gold, the thickness of 

 which must be very inconsiderable, since the natural volatiliza- 

 tion is sufficient to cause it to disappear entirely after a short 

 time. According to M. Fusinieri, these two metallic spots are 

 formed at the expense of the fused gold which the electric spark 

 contains. The deposit on the first face is nothing extraordinary ; 

 but, by adopting the explanation of the Italian philosopher for 

 the spot on the opposite surface, we are obliged to admit, that 

 the gold disseminated through the spark has passed, at least in 

 part, along with it through the whole thickness of the silver 

 plate ! It is unnecessary to add, that a spark issuing from a ball 

 of copper, gives rise to the same phenomena. 



The spark which emanates from a certain metal, does not 

 merely lose a portion of the molecules with which it was at first 

 impregnated, when it traverses another metal ; but it becomes 

 charged with new molecules at the expense of that metal. M. 

 Fusinieri even asserts, that, at each passage of the spark, reci- 

 procal changes are produced between the two metals ; that when 



