HENRY AND THE TELEGRAPH. 291 



conductors, all the positive elements could be associated together, as 

 also all the negative ones, so as to form virtually a single pair having loli 

 square feet of zinc surface, or any smaller area desired. In this manner 

 the apparatus could readily be transformed into a "quantity" battery, 

 or an " intensity " battery, at i)leasure. In the same year he constructed 

 for the laboratory a powerful "quantity" magnet, surpassing his Yale 

 College magnet; its lifting power, with a battery not exceeding one 

 cubic foot in bulk, beiug 3,500 pounds. In the following year, 1835, he 

 extended wires across the front campus of the college grounds, from the 

 upiier story of the library building to the philosoi^hical hall on the op- 

 posite side, through which magnetic signals were occasionally sent, dis- 

 tinguished by the liumber of tajis on the bell, as first exhibited by liim 

 four or five years earlier in the hall of the Albany Academy. Although 

 Henry had established the fact (contrary to all the antecedent expecta- 

 tion of physicists) that the most powerful form of magnet — the "quan- 

 tity" magnet — is not the form best adapted to distant action through an 

 extended circuit, the ingenious idea occurred to him that he could easily 

 combine such a system with the feebler "intensity" system, so as to 

 produce powerful mechanical action at almost any required distance. It 

 was simply necessary to appl^^ to the oscillating armature of the distant 

 "intensitv " magnet a suitable ])rolongation so arranged as to open and 

 close the short circuit of the adjoining "quantity" magnet of any a\ail- 

 able power. It was with his Princeton telegraph line, and its compar- 

 atively feeble magnet, that he undertook the experiment of breaking by 

 the mere lift of a small wire from a mercury thimble the "quantity" cir- 

 cuit of his monster magnet, and thus causing its heavy load to fall : — a 

 force scarcely safe if exerted through any sensible distance. He thus 

 fully illustrated the practicability of calling into action at a great 

 distance a power capable of producing the most energetic mechanical 

 effects.* 



1833. Ten years after the experimental telegraph of Schilling, Pro- 

 fessors Carl Friedrich Gauss and Wilhelm Edward Weber constructed 

 at Gottingen a galvanometer telegraph of single circuit from the Cabinet 

 of ]S"atural Philosophy to the Observatory, a distance of about a mile aud 

 a half. The two naked wires after the method of Weber were carried 

 over the houses and steeples of Gottingen, being supported by insula- 

 tors. The battery power being small, the receiving apparatus consisted 

 of a "multiplier" containing a very great length of fine silvered copper 

 wire; and the magnetic bar suspended by a silk thread carried on the 

 axis of suspension a small mirror, whose miuute deflections were observed 

 at the distance of ten or twelve feet through a telescope, t The telc- 



*Snuthso)uan Eeport for 1857, pp. 106, 112. 



tTliis appears to be oiio of the first employments of a reflecting galvanometer, an 

 inatrumeut which iu the hands of Sir William Tliomson has been brought to an ex- 

 treme degree of sensibility, and has rendered ocean telegraphy possible. As early as 

 1826, however. Prof. Christian J. Poggendorff applied the reflector to the magnetic 

 needle for accurately dcterniiuing miuute variations in its horizontal declination. 

 (Pogg. Annakn clcr FIii/s. iind Chcm. 1826, vol, vii. pp. 121-130.) 



