1863.] 



President's Address, 



37 



touch, they show signs of opposite electricities when separated. Mr. Gas- 

 siot showed, in 1844, that the same occurs when the metals are separated 

 by a thin stratum of air without having been in previous contact. 



2. The identity of voltaic with frictional electricity was denied by many, 

 because it gave no spark through an interval of air. Davy had indeed 

 asserted the contrary in his ' Elements of Chemical Philosophy,' but his 

 statement seems to have been doubted or unheeded. Mr. Gassiot, in the 

 Transactions for 1844, has put the fact beyond dispute; he showed that 

 by increasing the number of cells and carefully insulating them, sparks can 

 be obtained even with the feeblest elements. With 3520 cells, zinc and 

 copper excited with rain-water, he obtained sparks in rapid succession 

 through -^jjth. of an inch of air ; and a little later added to this a fact of still 

 higher significance, that by exalting the chemical action in the cells, the 

 same or even greater effect could be produced by a much smaller series. 

 The battery of 500 Grove's cells which was constructed for these experi- 

 ments is probably in some respects the most powerful that was ever made. 



3. The currents produced by electric or magnetic induction are of the 

 highest interest, and the employment of them as a source of electric power 

 is almost daily enriching physical science with precious results. In this 

 new field Mr. Gassiot has been one of the most successful explorers. So 

 early as 1839 he showed that the induction current gives a real spark, and 

 he found that in the flame of a spirit-lamp it could strike at a distance of 

 f ths of an inch. 



4. The splendid phenomena produced by the discharge of the induction 

 current through rarefied gases or vapours are well known ; in particular 

 the stratification of the light. The cause of this is not yet fully understood, 

 but Mr. Gassiot has made some very important additions to our knowledge 

 of it in the Bakerian Lectare for 1858 and his subsequent communications 

 to the Society. Am.ong these may be named his explanation of the occa- 

 sionally reversed curvature of the strata, and his discovery of the Recipro- 

 cating discharge, which, seeming single, is composed of two, opposite in 

 direction, but detected by the different action of a magnet on each of them — 

 a beautiful test, which is of wide application in such researches. Again, 

 the Torricellian vacuum which he used at first, even when absolutely free 

 from air, contains mercurial vapour : by applying to his tubes a potent 

 freezing mixture, he found that as this vapour condensed, the strata 

 vanished, the light and transmission of electricity decreased, till at a very 

 low temperature both ceased entirely. It follows from this that a perfect 

 vacuum does not conduct — a fact of cosmical importance, which had been 

 surmised before, but not proved ; and the desire of verifying this discovery 

 led him to a means of far higher rarefaction. A tube containing a piece of 

 fused hydrate of potassa is filled with dry carbonic acid, exhausted to the 

 limit of the air-pump's power, and sealed; then by heating the potassa, 

 the residual carbonic acid is mostly, or even totally absorbed. Vessels so 

 exhausted, though still containing vapour of potassa, and perhaps of water, 

 have a better vacuum than had been previously obtained, and often cease 



