550 TRANSACTION'S OF THE AMERICAN INSTITUTE. 



been seized upon to secure diiferent patents. I have also suc- 

 ceeded in modifying it so as to make it more portable ; my latest 

 arrangement is so small that a physician may place it in his 

 pocket, and by all that it is as powerful as the larger magneto- 

 electric induction apparatus in large boxes of ten to twenty 

 pounds weight, and patented over and over again. My arrange- 

 ment is not patented and may be seen in my laboratory. 



10. But as it requires less quantity of electricity to produce 

 sparks than to heat wire, and as sparks may be multiplied with 

 infinitely more economy than the heating of many pieces of wire 

 at each burner, I soon conceived the idea of applying the spark 

 of such a magneto-electric apparatus for this purpose. By the 

 usual construction, however, the wires in the coil are not care- 

 fully enough isolated to produce sparks so long that they may be 

 made available and many times sub-divided, and a large appa- 

 ratus is being constructed, expressly in this view. It consists of 

 a coil of soft iron wire, similar to that in the Rumhkorf coil, 

 but wound only with the careful isolated fine wire of several 

 thousand feet in length ; the large wire for the galvanic current 

 is omitted, as the iron coil is magnetized by the poles of power- 

 ful steel magnets, rapidly moved along its extremities. 



11. But there is another form of magneto-electric apparatus, 

 invented a few years ago in France. It consists of a bundle of 

 horse shoe steel magnets, powerfully charged, with their poles 

 rounded off, and the steel itself wound with the usual coil ; if 

 now in front of those magnets a soft iron in the shape of a com- 

 mon keeper is revolved, the rapid changes in the free magnetism 

 of the steel produces electric currents in the coil, more powerful 

 than if the coil is wound around the revolving piece, or soft pieces 

 of iron, as in the arrangement described under Nos. 9 and 10 

 above. Experience has confirmed me of this greater strength, a 

 fact which I, a priori, theoretically expected. I have both con- 

 structions, and many others besides, in comparative operation. 



12. I have projected and made provisional experiments with 

 two very different applications of this principle, by which the 

 power will increase so greatly that it will produce sparks amply 

 sufficient to light 100 or 200 burners, if not able to compete in 

 length of spark with the Rumhkorf coil, and will, like numbers 

 9 10 and 11, above, have the advantage over this coil of being 

 less expensive and independent of the galvanic battery, which, 

 besides, is a permanent trouble and expense, and if accidentally 



