402 



ELECTEICITY. 



of building grounds and apparatus, and required 

 too long and thorough training of the teachers, 

 to come into general use. Here was a system, 

 requiring, indeed, the possession of considerable 

 talent, tact, education, and imagination on the 

 part of the teacher, but rendering routine _im- 

 possible, -and promising showy and brilliant 

 results. 



ELECTRICITY. In connection with the 

 progress of electrical discoveries and theory, 

 the feature of most absorbing interest at the 

 present time, is that of the several propositions 

 and attempts toward establishing certain fixed 

 units of measurement for various electrical 

 quantities, and particularly 1, for the electro- 

 motive force of a galvanic couple or battery, i. e., 

 the total force of current the couple or battery 

 could generate if the resistance opposed to the 

 passage of such current through the conducting 

 wires or circuit be nothing or inappreciably 

 small ; 2, for the resistance opposed to the cur- 

 rent by the necessarily imperfect conducting 

 power of the wires or material of the circuit ; 

 3, for the actual intensity of the current pro- 

 duced, as a result of the given electro-motive 

 force diminished by the given resistance. The 

 determining of such units, as leading in time 

 to the ability to estimate accurately and com- 

 pare the electrical quantities of batteries and 

 circuits of all sorts whatever, and those requi- 

 site to the various effects which currents are 

 expected to produce, is at once seen to be a 

 problem the solution of which promises results 

 of the highest practical value. In the appli- 

 cations of electricity during the past year, al- 

 though perhaps no great or striking achievement 

 has been made, some points of interest never- 

 theless present themselves. (See also ATJROEAS, 

 METEOROLOGY, and TELEGRAPHY.) 



I. SCIENTIFIC PROGRESS. Measures of Elec- 

 tric Resistance. To determine comparatively 

 the resistances of different circuits, Mr. Siemens 

 had proposed that the standard or unit should 

 be a filament or minute column of mercury of 

 given length within a tube, and from the two 

 ends of which connections with the two poles 

 of a galvanic element or battery should be 

 made : a needle or other galvanometer intro- 

 duced in the course of the same circuit would 

 show the intensity of current when the mer- 

 cury filament is, and when it is not, made part 

 of the circuit, and would thus give the resist- 

 ance of the given length and diameter of that 

 metal as a conductor. An objection to this 

 plan is, that after a time alloy of the mercury 

 from the ends of the solid metal conductors 

 must occur, thus changing the actual conduct- 

 ing power of the filament, and again, that the 

 contact of the solid wires with the metallic 

 mercury is uncertain or of variable degree. To 

 obviate these difficulties, as well as certain im- 

 perfections in Wheatstone's electro-motive bal- 

 ance, Prof. W. Thomson has devised a new 

 electro-motive balance for determining resist- 

 ances of short bars or wires, and by use of 

 which he considers that no uncertainty in the 



connections can exist, even though these are 

 not made with extraordinary care. He con- 

 cludes, however, that in order to arrive at the 

 most accurate possible system of electrical 

 measures, the standards that may be adopted 

 must first have been exchanged between and 

 compared by different experimenters. For the 

 details of the paper, which is long and mainly 

 theoretical, the scientific reader is referred to 

 the proceedings of the Koyal Society, or to the 

 " Philos. Magaz.," Aug. 1862. 



Matthiesseii's Unit of Resistance is that 

 opposed to perfect conduction of an electric 

 current by a wire composed of 2 parts by 

 weight of gold and 1 of silver, length 1 metre 

 (39.37 in.), diameter 1 millimetre (.03937" in.). 

 The author's experiments lead him to conclude 

 that this alloy conducts electricity with nearly 

 the same facility at all temperatures between 

 32 and 212 F. ; that impurities in small quan- 

 tity do not sensibly affect its conducting power ; 

 and that the annealing of the metal also makes 

 no sensible difference. The wire should be 

 varnished to protect it from action of mercury. 

 (Pogg. Annalen, cxii, p. 353). Prof. "VV. Gibbs 

 suggests that the specific conducting power of 

 such a wire may, as is known to be the case 

 with copper, undergo change from continued 

 or repeated use. 



Weber's 'Proposed Absolute Standard. The 

 student of mechanics well knows that having 

 the measures of space and time, no specific fun- 

 damental measure of velocity is required ; since 

 we find or express velocity by the simple ratio, 

 to7- Weber calls attention to the fact that, in 

 like manner, if there are measures for electro- 

 motive force and actual intensity of current, 

 no specific fundamental measure of electric re- 

 sistance is necessary ; the resistance that exists 

 in a closed current in which the unit of electro- 

 motive force produces the xmit of intensity, 

 being taken as the unit of resistance. Now, 

 in Gauss's treatise on the "Intensity of the 

 Earth's Magnetic Force " (Gottingen, 1833), ab- 

 solute measures for terrestrial magnetism and 

 for bar magnetism are given. Weber shows 

 that from these an absolute unit of measure of 

 electro-motive force and a like unit of intensity 

 of current can be obtained these being ex- 

 pressed and known in the three simple elements 

 of space, time, and mass (of the conductor). In 

 some experimental applications of his principle, 

 employing a copper wire 3,946,000 millimetres 

 in length, and of a mass equal to 152,890,000 

 milligrammes (about 338 Ibs. avoird.), Weber 

 calculated the absolute measure of resistance 

 at 190,000,000 units, and the specific resistance 

 of the material at 1,865,600 units. ("Philos. 

 Magaz.," Sept. and Oct., 1861.) 



Electro-motive Force of Voltaic Piles. M. 

 Marie Davy believes that, however carefully 

 the units of resistance and of current may be 

 defined, since these are arbitrarily chosen, it 

 still cannot be hoped that from them we can 

 so estimate the electro-motive force of batter- 

 ies as directly to furnish the calorific value, or 



