42 WRITINGS OP JOSEPH HENRY. [1831 



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. A number of 

 other experiments would have been made to verify this had 

 not our use of the room been limited, by its being required 

 for public exercises. 



On a little consideration however, the above result does 

 not appear so extraordinary as at the first sight, since a cur- 

 rent from a trough possesses more " projectile force," to use 

 Prof. Hare's expression, and approximates somewhat in in- 

 tensity to the electricity from the common machine. May 

 it not also be a fact that the galvanic fluid, in order to pro- 

 duce the greatest magnetic effect, should move with a small 

 velocity, and that in passing through one fifth of a mile, its 

 velocity is so retarded as to produce a greater magnetic 

 action? 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 ap- 

 plicable to Mr. Barlow's project of forming an electro-mag- 

 netic telegraph ; * and it is also of material consequence in 

 the construction of the galvanic coil. From these experi- 

 ments, it is evident that in forming the coil we may either 

 use one very long wire or several shorter ones as the cir- 

 cumstances may require: in the first case, our galvanic com- 

 binations must consist of a number of plates so as to give 

 " projectile force ; " in the second, it must be formed of a single 

 pair. 



In order to test on a large scale, the truth of these pre- 

 liminary results, a bar of soft iron, 2 inches square and 20 

 inches long, was bent into the form of a horse-shoe, 9| 

 inches high, the sharp edges of the bar were first a little 

 rounded by the hammer, it weighed 21 lbs. ; a piece of iron 

 from the same bar weighing 7 lbs. was filed perfectly flat on 



*[In a statement made by Prof. Henry, in March, 1857, he says : "Not 

 being familiar with the historj'^ of the attempts made in regard to this inven- 

 tion, I called it ' Barlow's project,' while I ought to have stated that Mr. 

 Barlow's investigation merely tended to disprove the possibility of a tele- 

 graph."] 



