PHILOSOPHICAL SOCIETY OF WASHINGTON. 247 



sible diminution of the effect.* Professor Moll, the foremost of 

 Europeans in the chase, and close upon the heels of Henry in one 

 portion of his researches, produced a powerful "quantity" mag- 

 net, but one hopelessly and radically incapacitated from any 

 such application. 



These memorable consequences of careful and judicious ex- 

 periment, carried on in 1829, and 1830, formed truly a most 

 pregnant epoch in the history of the infant science ; and consti- 

 tuted a valuable addition to the world's capital. Their adoption 

 underlies all subsequent applications of the intermittent magnet, 

 and is the indispensable basis of every form of the electro-mag- 

 netic telegraph since invented. They settled satisfactorily (in 

 Barlow's phrase) — the "only question which could render the 

 result doubtful :" and though derived from the magnet, were 

 obviously as applicable to the galvanometer needle. 



It is idle to say in disparagement of these successes, that in 

 the competitive race of numerous distinguished investigators in 

 the field, diligently seaix-hing into the conditions of the newfound 

 agency, the same results would soon have been reached by others. 

 For of what discovery or invention may not the same be said ? 

 Only those who have sought in the twilight of uncertainty, can 

 appreciate the vast economy of effort, by prompt directions to 

 the path from one who has gained an advance. Not for what 

 might be, but for the actual bestowal, does he who first grasps a 

 useful truth, merit the return of at least a grateful recognition. 



If these results apparently so simple when announced by 

 Henry, have never been justly appreciated either at home or 

 abroad, no such complaint ever escaped their author. No such 

 thought seems ever to have occurred to his artless nature. For 

 him the one sufficient incentive and recompense was the advance- 

 ment of himself and others in the knowledge of nature's laws. 

 With the telegraph consciously within his grasp, he was well 

 content to leave to others the glory and the emoluments of its 

 realization. 



In the year 1831, Henry had suspended around the walls of 

 one of the upper rooms in. the Albany Academy, a mile of copper 

 bell-wire interposed in a circuit between a small Cruickshaiik 

 battery and an " intensity" magnet of continuous fine coil. A 

 narrow steel rod — a permanent magnet — pivoted to swing hori- 

 zontally like the compass needle, was arranged so that normally 

 when pointing north, this end remained in contact with one leg 

 of the soft iron core, while near the opposite end of the compass 

 needle, a small stationary office-bell was placed. At each exci- 



* Beyond a certain maximnm length, there is of course a decrease of 

 power proportioned to tlie increased resistance of a lonj conductor: l>nt 

 the magnetizing effect has not been found to be diminished in the ratio 

 of its length. 



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