Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

the original or inducing current of the battery with the greatest possible rapidity and uniformity ; and this is most beautifully accomplished in the best of these machines by the " trembler " of Dr. Neef. This is done by electro-magnetic power acting auto- matically on a magnet of soft iron, about which are made sev- eral coils of the large wire that forms the inner coil of the helix and connects with the battery. There is placed over the arms of this miniature magnet a silver spring that is faced and loaded like a hammer with a small bit of soft iron. This spring vibrates, with a mere hum from rapidity between the tips of the magnet and the end of an adjustable screw at its back, which is also tipped, but with a point of platinum ; and this strikes against a pin-head button of platinum attached to the silver spring. And here is the most delicate point in the whole apparatus. These platinum points should be riveted to their place, but never soldered. The solder will become decomposed by the electric spark that plays there, and after a while the machine appears to be uncertain, or even worthless, although perhaps a good machine in every other respect. The author must say he has seen not a few of such; and not only so, but he has often found the apparently good-sized helix stuffed with something, besides a thousand feet of insulated copper wire But to return. "We have said that the origi- nal current of the battery is interrupted by the magnetic force of attraction and repulsion acting upon the silver spring, which is inter- posed so as to separate, and join the contact or continuity of the battery wire. The bat- tery current renders the little soft iron a mag- net, and this attracts the spring-hammer, and that demagnetizes the little magnet which al- lows the spring to fly back again; and thus is the current made and broken more rapidly and uniformly by elec- tro-magnetic action than can be possibly done by any other me- chanical arrangement. I should also mention, that the face of the iron on the spring should be kept clean and bright, as well 13 Tar Fig. 19. Electro-Magnet.