Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/286

Rh 268 MAGNETISM hauseu. Von You Ettingsliausen l in the most recent research on the Ettings- subject with which we are acquainted has made determina tion of the susceptibility of bismuth by four different methods. The first of these was that formerly used by Toepler and himself, with the addition that the action of the bismuth bar was compared with that of a solenoid of as nearly the same dimensions as possible through which flowed a current of given strength (an artifice previously used by Christie). The second method consisted in measuring the force with which a portion of the diamag- netic substance hung in the axis of a coil and near one of its ends was repelled out of the coil when a known current passed through it. The third method was that of Rowland and Jacques. The fourth consisted in measuring the deflexion of a magnetometer needle produced by placing a piece of the diamagnetic substance between the poles of a powerful magnet under whose action the magnetometer needb had come to rest in the first instance. 2 The agreement between the results obtained by all the different methods was very fair considering the smallness of the effects to be measured in some of them. The second method is pronounced to be the best, and by means of it he gives also a determination of K for ferric chloride. Some of the results of the different experimenters for bismuth are given in the following table : Results for bismuth. Magnetizing Force. -106,. Authority, &c. 301 25-8 to 128 71-4 to 110-2 39-2 to 82-2 14-6 14-9 14-6 13-99 14-54 13-48 ( Calculated by Stoletow from cer- &amp;lt; tain results of Weber s, see ( Silow, Wied. Ann., 1882. j Calculated by Von Ettingshausen, ( I.e., from Weber. j Calculated by Von Ettingshausen, I.e., from Christie. / Three different samples by Von [ Ettingshausen s second method. ) Results for Most of the specimens contained slight traces of iron. Although the range of the magnetizing force in Von Ettingshausen s experiments was considerable, K was very nearly constant ; if there was any tendency to variation, it was decrease with the large magnetizing forces. The results for ferric chloride are not so concordant. Silow, after comparing his own earliest result (10 6 K = 81 ^ or a s l ut i n f density 1 475, magnetized by the earth s horizontal force) with those of Borgmann (10 6 /c = 48 8, density 1 87, magnetic force 40 to 59), concluded that the susceptibility of ferric chloride probably follows the same law as that of iron ; i.e., it first increases, then reaches a maximum, and afterwards decreases more or less slowly. His later experiments confirm this conjecture, and he finds that K has a maximum value for a magnetizing force of about -4 C.G.S. The smallest force used was about 08 C.G.S. and the corresponding value of 10 6 /c was 34; the largest value of 10 G /c occurring in his tables is 179. The values obtained in his last investigation are smaller than those given in his first table, but there is the same in crease and decrease. The following are his latest results : Silow. 1 106 K. i 106 K. 1-15 96 2-45 104 1-35 104 373 70 1-60 131 5-33 69 1-70 131 5-35 68 1-81 142 6-54 65 1-90 141 7-00 62 1-96 131 10-00 60 2-13 111 12-60 55 2-40 99 1 Wien. Ber., 1882. 2 This was one of the experiments adduced by Weber in the contro versy regarding diamagnetic polarity ; see Pogg. Ann., 1848. The unit of |p is the earth s horizontal force, presumably at Moscow. From the observations of Arndtsen on a solution of density 1 495 Silow 3 calculates 1 6 /c = 57 - 5 (magnetic force 20 3). For a solution of density 1-395, with magnetiz ing forces from 38 to 252, Schuhmeister gets 10 6 K=30 to 39. Von Ettingshausen, fora solution of density 1&quot;48, with magnetizing force 14 to 20, gets 10 6 = 59 to 56. The following are the values of 10 6 K obtained by Schuhmeister for various substances. JR 61 5 130-8 2-3i -7 Water - -55 -45 - 44 Alcohol - -45 - 42 - -38 - -46 39 &quot;37 Ether. - -40 - &quot;29 $ 66-8 141-8 27^-2 Oxygen from chlorate of potash ( 046 1 -056 059 067 122 128 Oxygen from electrolysis ozonized 1-117 181 177 Kitro^en 0278 0377 0496 ( 0232 0380 0437 RELATION OF MAGNETISM TO OTHER PHYSICAL PROPERTIES. Shocks, Jarring, or Vibration. The effect of these in aid ing the action of an inductive magnetic force was known to Gilbert; and it was also known to the earlier experimenters that the permanent magnetism of a body not subject to external magnetizing force was destroyed by like causes. The action is precisely similar to that found in the case of bodies temporarily or permanently deformed by mechanical stress, and, again, to the first effects of temperature on bodies temporarily or permanently strained, or temporarily or permanently magnetized. 4 The effect may be conceived as consisting of a loosening of the molecules for the moment, so that they follow more easily any force acting on them whether mechanical or magnetic. The following parallel statements, taken from the results of Wiedemann, who has devoted much careful study to these phenomena, will sufficiently illustrate the matter : I. Jarring a bar under mague- Wiede- tizing force causes increase of mann s magnetization. parallel II. Permanent magnetization state- in a bar is diminished by jarring, ments. III. A bar permanently mag netized and then partly demag netized loses or gains magnetiza tion according as the demagnet ization is small or great. 5 Minuter details regarding the effects of jarring will be found in memoirs by Wiedemann, Fromme, Auerbach, and others already quoted. The reader may also consult Warburg, Po/jg. Ann., 1870, and Villari, Fogg. Ann., 1869. Mechanical Strain produced by Magnetization. The Joule s starting point of accurate research on this subject was the dis discovery made by Joule 6 in 1842 that a bar of soft iron ^ J lengthened when it was temporarily magnetized in the magnet longitudinal direction. When the magnetizing force was strains. removed the bar shortened, but in general not quite to its 3 Wied. Ann., 1882. 4 Compare also the effect of the same causes on the temporary and residual charge of Leyden jars, art. ELECTRICITY, vol. viii. p. 40. 6 It is possible in this way even to cause a wire to reverse its twist and a bar to reverse its magnetization by jarring. 6 His attention had been drawn to the subject in 1841 by a Mr Arstall, who had suspected the existence of some such effect. Joule s papers on the subject are in Sturgeon, Ann. of EL, 1842, and Phil. Mag., 1847. 1. Jarring a body under twist ing stress causes increase of twist. 2. Permanent twist in a wire is diminished by jarring. 3. A wire permanently twisted and then partly untwisted loses or gains twist when jarred according as the untwisting is small or great. 5
 * -103