MEMOIR OF OERSTED. 177 



Lad, in 179'2, invented tlio aerial telegraph, recall the tact that the Gauls had 

 transmitted distant signals by means of wooden beams set in motion. Neither 

 the Ganls nor the older physicists had created any regular means of correspond- 

 ence. 



Among those whom I have the honor of addressing, several may be able, like 

 mvself, to recall the memorable lectures which M. Ampere delivered at the Col- 

 lege of France at the commencement of 1S32, in which he had the boldness to 

 express his ideas on the relations of the structure of different classes of animals 

 in contradiction to Cuvier, who lectured in the adjacent amphitheater; ingenious 

 ideas wliich M. Cuvier overwhelmed at each lecture with peremptory facts, 

 and which M. Ampere, accommodating himself to those facts, reproduced still 

 more ingeniously in his subsequent lecture. In this course, naturally much 

 frequented, and which was in substance a course of experimental physics, M. 

 Ampere spoke one day of electrical currents, and, after having represented on 

 the table four small magnetic needles with metallic wires suitably encompass- 

 ing them, he explained how an electric current transmitted at will in such 

 or such a manner, by means of these wires, would cause a declination of such or 

 such of these needles in definite directions, so as to produce divers combinations, 

 to each of which might be attributed the value of one of the letters of the 

 alphabet ; how, in fine, by varying at will and with the rapidity of writing the 

 mode of propagation of the electric current, words, phrases, discourses might be 

 formed by the succession of these conventional letters. 



'M. Ampere particularly cherished this idea and often recun-ed to it in con- 

 versing with his friends ; but his fertile imagination did not stop with a single 

 process, and sometimes, instead of needles, he proposed the employment of vases 

 tilled with water in which should be produced alternately disengagements of 

 oxygen and hydrogen by the decomposition of the liquid. On the whole, it is 

 impossible to deny that from that time the fundamental idea of a future electric 

 telegraph existed among the auditors and friends of M. Ampere. There 

 remained nothing more" than to execute it practically. Such execution was 

 rendered much more easy by the result of the experiments of M. Ai-ago on the 

 momentary magnetization of soft iron by the electric current, and by the 

 knowledge of the laws of the remarkable phenomenon of induction, established 

 by M. Faraday. 



Every one knows how, from station to station, long metallic threads, placed 

 on insulating supports, have been stretched in order to transmit the electric cur- 

 rent from point to point. In the first arrangements of apparatus for this pur- 

 pose, in that especially which M. Wlieatstone established between Paris and 

 Versailles and which was in operation in 1S45, the electric current was produced 

 by magnets, for which was afterwards substituted an electric battery, as being 

 susceptible of more energetic action. The conducting wires were reduced, for 

 each apparatus, to a single one, the mass of the earth sullicing for the return of 

 the current. The needles were also reduced to a single one, which stopped in 

 any desired positicjn before a dial-plate bearing on its circumference the 25 let- 

 ters of the alphab(;t, the 10 numerals, points, &c. To bring the needle to a 

 certain radius of the dial and to a definite letter, the dentated wheel on which 

 it de})ended was made to traverse a suita])le luimber of notches, by as often 

 interrupting and re-establishing the electric current. This idea of suspending 

 and restoring the current l)y interruptions variously diversified, was the most 

 essential addition which had been made to the fundamental idea of Ampere. 

 The interruptions and re-establishments of the current occasion, so to speak, a 

 succession of electric waves, comj)arable, in a certain measuj-e, to the sonorous 

 waves by means of which our voice is i)ro})agated, but iniinitely more rapid. 



Since these first essays, the mechanism emi)loyed has l)een singularly varied, 

 "^i'lie dials and needles have been suppressed and re])laced by other combinations. 

 A multitude of ingeni(jus instruments, cut-offs, iJole-tluuHjcrs, manipulators, 

 12 s 



