DISCOURSE OF W. B. TAYLOR. 225 



a small galvanic pair 2 inches square, acting through the same 

 length of wire (over 1000 feet,) "the magnetism was scarcely ob- 

 servable in the horse-shoe." Employing next a trough battery of 

 25 pairs, having the same zinc surface as previously, the magnet in 

 direct connection, (which before had supported four and a half 

 pounds,) now lifted but seven ounces; not quite half a pound. 

 But with the 1060 feet of copper wire (a little more than one-fifth 

 of a mile) suspended several times across the large room of the 

 Academy, and placed in the galvanic circuit, the same magnet sus- 

 tained eight ounces : that is to say, the current from the galvanic 

 trough produced greater magnetic effect after traversing this length 

 of wire, than it did without it. 



" From this experiment it appears that the current from a gal- 

 vanic trough is capable of producing greater magnetic effect on 

 soft iron after traversing more than one-fifth of a mile of inter- 

 vening wire than when it passes only through the wire surrounding 

 the magnet. It is possible that the different states of the trough 

 with respect to dryness may have exerted some influence on this 

 remarkable result ; but that the effect of a current from a trough if 

 not increased is but slightly diminished in passing through a long 

 wire is certain." And after speculating on this new and at the 

 time somewhat paradoxical result, suggesting that "a current from 

 a trough possesses more ' projectile' force (to use Professor Hare's 

 expression,) and approximates somewhat in 'intensity' to the elec- 

 tricity from the common machine," Henry concludes: "But be 

 this as it may, the fact that the magnetic action of a current from 

 a trough is at least not sensibly diminished by passing through a long 

 wire, is directly applicable to Mr. Barlow's project of forming an 

 electro-magnetic telegraph;* and it is also of material consequence 

 in the construction of the galvanic coil. From these experiments 

 it is evident that in forming the coil we may either use one very 

 long wire, or several shorter ones, as the circumstances may require : 

 in the first case, our galvanic combination must consist of a num- 



*[ Really AMPERE'S project, not BARLOW'S. In a subsequent paper HENRY cor- 

 rected this allusion by saying, "I called it 'Barlow's project,' when I ought to 

 have stated that Mr. Barlow's investigation merely tended to disprove the possi- 

 bility of a telegraph."] 



15 



