ELECTRICITY. 



407 



perpendicular to the axis of the helices, alter- 

 nately running from the inner to the outer 

 and from the outer to the inner diameters of 

 the outer helix, and very carefully insulating 

 not only between these strata but also between 

 the inner and the outer helix. By these jneans 

 he had in July of the year named produced an 

 instrument giving sparks of 9 to 12 inches in 

 length. Meanwhile, M. Ruhmkorff T s best im- 

 proved instruments had failed to give sparks of 

 more than 3 or 4 inches in length. In the sum- 

 mer of 1858, Prof. R. S. MacCulloh, of Columbia 

 College, X. Y., having secured for that institu- 

 tion one of these coils which, with a battery 

 of only 4 Bunsen's cells, gave a spark 12 inches 

 in length, ordered also one of Ruhmkorff's for 

 which the French Academy had just awarded 

 him a prize, and informed him of the power of 

 Ritchie's machine, as also of the readiness pro- 

 fessed by the latter maker to surpass the power 

 of any instrument that might be so furnished. 

 Receiving in the mean time no instrument from 

 Paris, Prof. MacCulloh, in May, 1859, while on 

 a tour in Europe, visited M. Ruhmkorff, who 

 expressed an unwillingness to produce an in- 

 strument upon the conditions named, but 

 showed one which he had attempted, and 

 which had destroyed itself by the breaking of 

 the spark through the insulation. Prof. Mac- 

 Culloh, supposing that Ruhmkorff would be 

 glad to compare Ritchie's instruments with his 

 own and those of Hearder, and that he would 

 of course accord due credit for what was origi- 

 nal in the first named, presented him with one 

 of these giving sparks of 7 inches. This M. 

 Ruhmkorff dissected, for the purpose of ex- 

 amining its construction. About the same time, 

 Prof. MacCulloh ordered of Ritchie the most 

 powerful coil he could make, to be sent to Paris. 

 Being received in November, this instrument 

 and its performance were by him exhibited be- 

 fore Jacobi, Foucault. Duboscq, Jamin, Desains, 

 Froment, and others distinguished in electrical 

 or general physical science, as well as before 

 the students of the Ecole de Medecine, and sev- 

 eral professors of the Polytechnic School. M. 

 Ruhmkorff, meantime, had a long-unfulfilled 

 contract for a powerful coil for the last named 

 school ; and M. Jamin expressed himself in 

 favor, in case such instrument should not be 

 delivered by the close of the term of contract 

 (March, I860), of procuring one of Mr. Ritchie's 

 instruments. In March, however, Ruhmkorff 

 delivered to the school an instrument of his 

 construction ; and Prof. MacCulloh, on seeing 

 this coil in May, was informed by M. Jamin that 

 it was wound in portions perpendicular to the 

 axis (Ritchie's system), and that it gave sparks 

 of about the same length as the most powerful 

 instrument of the latter, namely. 13 to 16 

 inches. M. Ruhmkorff showed to Prof. Mac- 

 Culloh in June another instrument of like 

 power, and of which he declared the construc- 

 tion to be similar. These facts are chiefly 

 drawn from an account furnished to Mr. Rit- 

 chie for publication, by Prof. MacCulloh, since 



Harris 100.0 



Buff 95.4 



Pouillet 73.0 



Arndtsen 93.7 



his return. The French scientific writers and 

 journals, however, seem uniformly to ignore 

 Ruhmkorff's indebtedness to Mr. Ritchie for an 

 improvement which has fully tripled the power 

 of the machine over that of any constructed by 

 the previous methods ; and they unite in award- 

 ing to the Parisian maker the entire credit of 

 the invention of another. The Abbe Moigno, 

 editor of the Cosmos, relates witnessing about 

 the beginning of 1862 an experiment with one 

 of Ruhmkorff's coils, which gave a spark 18 

 inches long, and pierced glass of two inches 

 thickness. (See llechan. Effects, &c., previous.) 

 Conducting Power of Pure and Alloyed Cop- 

 per. Matthiessen and Holtzmann have pre- 

 sented before the Royal Society a paper on the 

 effect of the presence of metals and metalloids 

 upon the electric conducting power of pure 

 copper. The variations in conductivity of 

 copper wires as found by different experiment- 

 ers, must depend in part on differences of qual- 

 ity and purity of the wires experimented with, 

 and in part, at least, also on differences in tem- 

 perature. Thus, taking the conducting power 

 of pure silver as =100. the following are the 

 measures for copper as found by the physicists 

 named : 



Becquerel 95.3 



Riess 67.2 



Lenz 73.4 



Davy 91.2 



Christie 66.0 



The temperatures at which the determina- 

 tions were made are given only in the cases of 

 Becquerel, Lenz, and Arndtsen, namely, 32 = F. 

 Matthiessen and Holzmann prepared pure cop? 

 per, both by a method involving precipitation 

 with sulphuretted hydrogen from the purest 

 commercial sulphate of copper, and also by pre- 

 cipitating the metal galvano-plastically by a very 

 weak current from the same compound. The 

 conductivity of a hard-drawn silver wire being 

 taken as = 100, the mean of 12 determinations 

 of hard-drawn wires from the copper so ob- 

 tained gave for this metal 93.08, at 18.9 C. 

 "With similar wires annealed, there was a gam 

 of 2.5 per cent., the mean in this case being 

 95.58. Copper fused in the air is probably al- 

 ways contaminated in degree with oxygen which 

 it absorbs, producing some quantity of the sub- 

 oxide ; and the presence of this impurity was 

 found always to reduce the conducting power, 

 and in some cases to as low as from 69 to 73 in 

 the scale. The experimenters could not induce 

 the taking up by copper of more than .05 per 

 cent, of carbon ; but even this reduced the con- 

 duction to 74.91, at 18.3 0. Phosphorus, sul- 

 phur, selenium, and tellurium all very consid- 

 erably reduced the conducting power of copper 

 into which they entered as impurities ; and ar- 

 senic in a still more remarkable degree 5.4 

 per cent, of arsenic giving a mean conducting 

 power of only 6.18, at 16.8 C. ; and 2.8 per 

 cent, of 13.14", at 19.1 C. Of all the metallic 

 impurities tin and iron most sensibly lowered 

 the conducting power, the former, in amount 



