Franklin, Dutliy wul Ampere. 485 



a metallic rod or the coils of an electro-magnet, secondary 

 waves are induced, called secondary currents. It seems rea- 

 sonable to ascribe these waves to the same shifting of the 

 poles which produces the sonorific undulations*. 



* Tliese phaenomena excite more interest in consequence of the employ- 

 ment, for medical purposes, of an apparatus originally contrived by Cal- 

 lan, but since ingeniously modified by our countr\nian, Dr. Page, into a 

 form which has been designated as the electrotome. A coil of coarse cop- 

 per wire, covered with cotton, like bonnet wire, is wound about a wooden 

 cylinder. Around the coil thus formed, a coil of fine copper wire similarly 

 covered is wound, leaving the extremities accessible. One end of the 

 coarse coil communicating constantly with one pole of a galvanic battery, 

 the other end is left free; so that by scraping with it the teeth of a rasp 

 attached to the other pole, a rapid closing and opening of the circuit may 

 be effected. Under these circumstances, an observer, holding the ends of 

 the fine coil, receives shocks more or less severe, according to the construc- 

 tion of the battery, the energy of the agents employed to excite it, or the 

 total weight and relative dimensions of the coils, as to length and sectional 

 area. Agreeably to the received doctrine, the shocks thus produced are 

 owing to secondary currents caused by dynamic induction. Agreeably to 

 the hyjiothesis which I have advanced, the atoms of the coarse wire, pola- 

 rized by waves proceeding from the poles of the battery, induce a corre- 

 sponding polarizationof the atoms of thefine wire; the aggregate polarity im- 

 parted being as the number of atoms in the former to the number of atoms 

 in the latter; or (to use an equivalent ratio) as the weight of the coarse 

 to the weight of the fine wire. But as on breaking the circuit, through the 

 coarse wire, the sethereo-ponderable atoms in both wires resume their neu- 

 tral positions, while this requires each circuit to be run through within the 

 same minute interval, the velocities of their respective waves will be in- 

 versely as their sectional areas and directly as their lengths ; in other words, 

 the velocity of the fine wire will be as much greater as the channel whicli 

 it affords is narrower and longer. The cylinder, included within the coils 

 as above stated, being removed, a cylindrical space is vacated. If into the 

 cavity thus made, iron rods, like knitting needles, be introduced, one after 

 the other, while the apparatus is in operation, the shocks increase in seve- 

 rity as the number augments ; so that from being supportable they may be 

 rendered intolerable. The shock takes place without the presence of iron, 

 but is much increased by its assistance'. 



These facts ajjpear to me to justify a surmise, that the aethereo-ponde- 

 rable atoms of iron, in becoming magnetized and demagnetized, co-operate 

 with the aethereo-ponderahle atoms of the copper coils in the induction of 

 secondary undulations. It is conceived that these may be owing to the in- 

 testinal change,, attended by sound, as above stated (73) ; this being caused 

 l)y a sudden api)roximation of the poles of the atoms, previously moved 

 apart by the influence of the galvanized coil. But if this sudden coming 

 together of the previously separated poles of atoms within a magnetized 

 cylinder of iron can contribute to the energy of secondar}' waves, it is con- 

 sistent to infer that these waves owe their origin to an analogous a|)proxi- 

 niation of the separated poles of the cupreous atoms, forming the finer coil, 



' Agreeably to the usual construction, the cylinder about which the 

 inner coarse wire coil is wound is originally of iron, so that there is as 

 much of this metal contained as it can hold. Various contrivances are re- 

 sorted to for tiie closing and opening of the circuit, which arc more inge- 

 nious and convenient than scraping a rasp, as above described. 



