1819.] and a new Galvanic Instrument. 181 



being plunged in one vessel. I have usually separated the pairs 

 by a board, extending across the frame merely. 



Indeed when the 40 plates were successively associated in 

 pairs of copper and zinc, though suspended in a fluid held in a 

 common recipient without partitions, there was considerable 

 intensity of galvanic action. This shows that, independently of 

 any power of conducting electricity, there is some movement in 

 the solvent fluid which tends to carry forward the galvanic prin- 

 ciple from the copper to the zinc end of the series. I infer that 

 electro-caloric is communicated in this case by circulation, and 

 that in non-elastic fluids the same difficulty exists as to its retro- 

 cession from the positive to the negative end of the series, as is 

 found in the downward passage of caloric through them. 



It ought to be mentioned, that the'connecting wire should be 

 placed between the heterogeneous surfaces before their immer- 

 sion, as the most intense ignition takes place immediately 

 afterwards. If the connexion be made after the plates are 

 immersed, the effect is much less powerful ; and sometimes after 

 two or three immersions, the apparatus loses its power, though 

 the action of the solvent should become in the interim much 

 more violent. Without any change in the latter, after the plates 

 have been for some time suspended in the air, they regain their 

 efficacy. I had observed in a galvanic pile of 300 pairs of two 

 inches square a like consequence resulting from a simultaneous 

 immersion of the whole. (See Plate XCV1, fig. 3.) The bars 

 holding the plates were balanced by weights, as window sashes 

 are, so that all the plates could be very quickly dipped. A platina 

 wire, No. 18, was fused into a globule, while the evolution of 

 potassium was demonstrated by a rose-coloured flame arising 

 from some potash which had been placed between the poles. 

 The heat, however, diminished in a few seconds, though the 

 greater extrication of hydrogen from the plates indicated a more 

 intense chemical action. 



Agreeably to an observation of Dr. Paterson, electrical 

 excitement may be detected in the apparatus by the condensing 

 electroscope, but this is no more than what Volta observed to be 

 the consequence of the contact of heterogeneous metals. 



The thinnest piece of charcoal intercepts the calorific agent, 

 whatever it may be. In order to ascertain this, the inside of a 

 hollow brass cylinder, having the internal diameter two inches, 

 and the outside of another smaller cylinder of the same sub- 

 stance, were made conical and correspondent, so that the 

 greater would contain the less, and leave an interstice of about 

 one-sixteenth of an inch between them. This interstice was 

 filled with wood, by plugging the larger cylinder with this mate- 

 rial, and excavating the plug till it would permit the smaller 

 brass cylinder to be driven in. The excavation and the fitting 

 Of the cylinders was performed accurately by means of a turning 



