NATURAL PHILOSOPHY. 155 



with thread, there is a complete circuit for every current induced in each sec- 

 tion of everv wire. Secondly, the cm-rents in the various sections of the 



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iron do not oppose each other ; but the currents in each section of every 

 wire are opposed by the currents flowing in the surrounding wires. Thirdly, 

 in the iron coil all the currents in the various spirals flow in the same direc- 

 tion, and form one strong current, which may be used by connecting the 

 ends of the coil with any body to which we wish to apply its force. But in 

 the common cores all the currents in the sections of each wire remain within 

 the wires, and cannot be used. Fourthly, the effect of the condenser on the 

 currents produced in the iron core can be ascertained when an iron coil is 

 used, but not with the common cores. By using an iron, coil as a core, it is 

 found that the condenser increases the intensity of the currents induced in 

 the core. Fifthly, the ends of the iron coil, used as a core, may be connected 

 with the coatings of a Leyden jar, and then the sparks from the coil are di- 

 minished in length, but increased in brightness. By the use of cores consist- 

 ing of coils of insulated iron wires, electrical currents of considerable quan- 

 tity and intensity may be obtained. These currents of quantity and intensity 

 may answer for working the Atlantic telegraph, and for producing the elec- 

 tric light. Besides the cores just described, and the common core, Professor 

 Callan used three other kinds of cores, viz : a flat or elliptical bundle of 

 wires ; a core made by coiling uninsulated iron wire on an iron bar ; and a 

 core consisting partly of a bundle of iron wire, and partly of a coil of insu- 

 lated iron wire. The fourth result of his experiments is a new mode of in- 

 sulation, in which imperfect insulation is used when imperfect insulation is 

 sufficient, and perfect insulation is employed where such insulation is re- 

 quired. The advantage of this mode of insulation is, that each spiral in the 

 secondary coil is brought nearer to the other spirals, as well as to the primary 

 coil and core, than it can l:c in the common method of insulation, without 

 at all diminishing the efficiency of the insulation. A coil in which the sec- 

 ondary wire was iron, and insulated in the manner described, was shown to 

 the meeting, which, with a single cell, six inches by four, gave sparks half 

 an inch long without a condenser. The insulation of the large condensers 

 made by Professor Callan, in which the acting metallic surface of each plate 

 exceeded GOO square feet, gave way before the coil which he exhibited was 

 made ; and, therefore, he could not say what the length of the sparks would 

 be with the aid of a condenser. But were a condenser of the proper size to 

 have the effect of increasing the sparks in a thirty-fold ratio, as in M. Gas- 

 siot's great coil, the length of the sparks produced by Professor Callan's coil 

 with a single cell should be fifteen inches. The outer diameter of the coil 

 was about four inches, its length twenty inches, and the length of the second- 

 ary coil about 21,000 feet. The fifth result is, a contact-breaker in which 

 the striking parts are copper, and which acts as well as if they were platina. 

 The sixth result is a mere explanation of the condenser, which is confirmed 

 by the effect of the condenser on the electrical currents produced in the core. 

 The last result consists in the discovery of some new facts relating to the 

 condenser, from some of which it follows, that the ordinary mode of making 

 the condenser is defective ; for condensers are generally made so that the 



