444 Mr. J. N. Hearder on a new Arrangement of 



which I have recently constructed, and which I am about to 

 describe, these phsenomena are more strikingly evident ; and but 

 for the arrangement which I have adopted, I believe that they 

 would not have been developed. 



3. The machine consists of a gutta-percha bobbin of about 12 

 inches in length, the cylindrical centre of which is large enough 

 to receive the primary coil with its core. Upon this bobbin is 

 wound the secondary coil, consisting of fine copper wire covered 

 with silk, and carefully varnished with shell-lac, which is allowed 

 to dry previously to winding on. The consecutive layers of the 

 wire are separated from each other by a stratum of oiled silk or 

 sheet gutta-percha. I am thus enabled to wind off and relay 

 the wire to repair accident ; and I have more than once found 

 the advantage of the arrangement; for, on forcing my first 

 machine to a very extreme point of tension, the internal insula- 

 tion broke down, and on winding off the wire I discovered the 

 cause of the accident, and was able to apply the appropriate 

 remedy. The contact breaker which I employ is similar to that 

 of my medical coil machine, consisting of a very stiff brass spring, 

 armed at one end with a piece of iron, to be attracted by the 

 end of the iron core, and breaking contact by means of a platina 

 stud fixed about the centre of its length, and pressing against a 

 contact screw also armed with platina. The condenser is, as in 

 Kuhmkorff^s machine, enclosed in the base of the instrument. 

 The secondary coil is rather less than three miles in length. My 

 exciting battery is a modification of Grovels nitric acid battery, 

 the zinc being excited with muriate of ammonia instead of dilute 

 sulphuric acid, by which the amalgamation of the zinc is dis- 

 pensed with, and the battery is in every respect equally powerful. 

 With twelve cells the following effects are produced with the 

 coil. 



4. The spark at the interruptor is loud, brilliant, and flame- 

 like, frequently throwing out a flat sheet of flame of a peculiarly 

 distinctive character, as large as a shilling, or even larger. By a 

 connecting screw the condenser can be detached, when the ordi- 

 nary secondary spark appears at the break very different from 

 that which occurs when the condenser is used. 



5. Each secondary terminal gives sparks to an uninsulated 

 conductor, which are longer when the opposite terminal is com- 

 municating with the ground, sometimes more than an inch in 

 length ; and on connecting the terminals with a graduated Lane's 

 discharger furnished with platina points, torrents of sparks in 

 bundles pass between them at a distance of 2*5 inches. At 2*75 

 sparks still pass, but not in such quantities ; and on modifying 

 the vibrations of the spring with the finger, so as to vary slightly 

 the pressure, occasional sparks will pass nearly 3 inches in length. 



6. On approximating the points to within 0*4 or 0*5 of an 



