326 Experiments on the TranfmiJJion of 



prifmatic fjJcflrum ; and their power was found to be increafing, while their refrangibllity 

 was leflened as far as to the confines of red-coloured light. But their diminifliing 

 refrangibility and increafing power did not ftop here } for they have been purfued a con- 

 fiderable way beyond the prifmatic fpeBrum, into an invifible (late, ftill exerting their 

 increafing energy, with a decreafe of refrangibility up to the maximum of their power ; 

 and have alfo been traced to that (late where, though dill lefs refra£led, their energy, on 

 account, as may be fuppofed, of their now failing denfity, decreafed pretty fall ; after 

 which the invifible thermometricat fpeElrum foon vanilhed. 



If this be a true account of folar heat, for the fupport of which he appeals to his ex- 

 periments, he concludes that we muft admit that fuch of the rays of the fun as have the 

 refrangibility of thofe which are contained in the prifmatic fpe£lruna, by the con(lru£lion 

 of the organs of fight, are admitted under the appearance of light and colour ; and that 

 the reft, being ftopped in the coats and humours of the eye, aft upon them, as they are 

 known to do upon all the other parts of our body, by occafioning a fenfation of heat. 



VII. 



Additional Experiments on Galvanic EleElricity. By Mr, Davy, Superintendant of the 



Pneumatic Injlitution. 



To Mr. NICHOLSON. 

 S I R, 



HE earlier experimenters * on animal eleftricity noticed the power of well burned 

 charcoal to conduft the common galvanic influence. 



I have found that this fubftance polTelTes the fame properties as metallic bodies in pro- 

 ducing the (liock and fpark f when made a medium of communication between the ends 

 of the galvanic pile of Signor Volta. 



I have likewife found that perfeftly well made charcoal, when connefted with water or 

 aqueous folutions in the galvanic circuit, elFefts changes in them analogous to thofe pro- 

 duced by metals ; but connefted with peculiar appearances. 



I . Two long and thin (lips of dry charcoal were connefted with filver wires attached to 

 the ends of a galvanic pile of 60 pieces. The points of the charcoal (lips were immerfed 

 in a glafs of water, at the diftance of half an inch from each other ; and the globules of 

 air adhering to them being carefully removed, the communication made fure. 



In about a minute, particles of gas began to form and evolve themfelves round the point 

 of the charcoal connefted with the filver fide of the apparatus. Near a quarter of an hour 



• The inventor of the galvanic pile difcovered the condu£ling power of charcoal. His experiments were 

 confirmed by Creve and Schmuck. See PfafF on Animal Eleftricity, page 4s. 

 t The fpark is mod vivid when the charcoal is hot. 



elapfedj 



