XA rURE 



[July 9, 1896 



field of sufficient strength to force the molecules to maintain a 

 direction parallel to that of the field. If hysteresis is due only 

 to the formation of new combinations and not to mechanical 

 restraint, then under these conditions it will vanish altogether. 



Kxperiments were carried out to verify this deduction. A 

 finely laminated cylinder of iron was suspended on its axis 

 between the poles of a rotating electro-magnet, but was 

 restrained from continuous rotation by a spring. On rotating 

 the magnet, the armature was dragged round until the restoring 

 force of the spring equalled the force due to hysteresis, and 

 the value of the latter could be obtained from the observed 

 deflexions. At first the value of the hysteresis was higher 

 than that in an alternating field for corresponding inductions, 

 but at an induction of about 16,000 in soft iron and 15,000 in 

 hard steel the hysteresis reached a sharply defined maximum 

 and rapidly diminished on more complete magnetisation, until 

 at an induction of about 20,000 it became very small with 

 every indication of di.sappearing altogether. Soft iron and 

 hard steel gave very similar curves, and in both the curve of 

 hysteresis-induction cut the curve obtained from the values in an 

 alternating field at a point just before the maximum. The 

 result fully bears out the deduction from the theory, and proves 

 in addition that hysteresis is not .sensibly due to anything of the 

 nature of mechanical restraint of the molecules. The form of 

 the curve also gives clear indications of the three stages of 

 molecular movement, the first stage giving a slowly rising curve, 

 the second a straight rapid rise, and the third a straight and 

 much more rapid descent. 



Further experiments were carried out on the effect of speed of 

 rotation. In an alternating field the speed of reversal has been 

 .shown to be without sensible effect on the hysteresis, and theory 

 points to this result as a natural deduction. From an extremely 

 slow speed up to seventy revolutions per second no definite 

 change was found in the value of the hysteresis. At the same 

 time several small modifications were noted, produced by rapid 

 variations in the speed of rotation or magnetising force. The 

 effect lasted through many revolutions, but ultimately the same 

 steady condition was arrived at. At and near the maximum 

 value the hysteresis was very variable. The effects were much 

 more marked in soft iron than in hard steel, as would be 

 anticipated from the theory of their con.stitution. 



June II. — "The Relation between the Refraction of the 

 Elements and their Chemical Equivalents." By Dr. J. H. 

 (Jladstone, F.R.S. 



This paper is intended to give a preliminary account of .some 

 recent investigations into the specific refraction of the elements. 

 The first part contains the atomic weights, with the specific 

 and atomic refractions of fifty-five of the elements. 



The specific refraction cannot claim a constancy equal to that 

 of the atomic weight. Several of the elements exhibit two or 

 more values, besides many smaller variations scarcely, if at all, 

 beyond the limits of experimental error, which depend upon 

 differences of physical condition or chemical combination. 



The .second part deals with a law ]ireviously suggested by the 

 author, namely, that the "specific refractive energy of a metal 

 is inversely as the square root of its combining proportion." 

 The product of these two quantities as determined from their 

 compounds is found to be for 5 univalent metals about 1-3, for 

 10 bivalent metals about 099, for 7 trivalents about I '01, for 

 6 quadrivalents about I 06, and for one quinquivalent 098. 



The observations show : First, that the metals which have the 

 same valency, have the same, or nearly the same, constant of 

 refraction for equivalent weights. Secondly, that the constants 

 of the bivalent, trivalent. quadrivalent, and apparently quin- 

 quivalent groups are practically the .same, ranging about I 'oi. 

 Thirdly, that when a metal combines in a proportion that 

 indicates a lower valency than that ordinarily as.signed to it, its 

 constant is somewhat elevated. 



The relation involved is not between the optical property and 

 the atomic weight, but between it and the electro-chemical 

 equivalent. 



It is proposed to give this product the descriptive name, 

 " Refractive constant of equivalent weights." It may be repre- 

 sented by — 



SI-,^ = constant, or by S-E = constant, 



where S is the specific refraction, anil E the chemical equivalent 

 of the metal. 



The Lorenz expression for S may be equally used if preferred. 



\(). 1393, vol.. 54J 



This is suggested as a first approximation to a law, which 

 holds good, however, only for the metallic elements, and that 

 when they are electro-posiitive radicals. 



"The Effects of a strong Magnetic Field upon Electric Dis- 

 charges in Vacuo." By A. A. C. Swinton. 



This paper deals with some effects of a strong magnetic field 

 upon electric discharges in vacuo. 



A pear-shaped Crookes' tube was suspended with the kathode 

 terminal uppermost above the pole of a very powerfid electro- 

 magnet. 



When the magnet was not excited the walls of the tube 

 showed everywhere green fluorescence, which was especially 

 strong over the rounded end of the tube opposite the kathode. 

 When the magnet was magneti.scd, the whole appearance of the 

 discharge was found to alter immediately to what is shown in the 

 illustration (Fig. i). l^xcepling for a lillle near the kathode and 



a very bright spot at the bottom immediately over the centre of 

 the magnet pole, all the green fluorescence disappeared, while 

 extending from near the kathode to the bright spot at the bottom 

 of the tube a very bright cone of blue luminescence made its 

 appearance. 



When under these conditions the tube was moved sideways, 

 the bright spot at the apex of the cone and the cone itself 

 moved, the spot and apex always maintaining a position exactly 

 over the centre of the magnet pole. 



At the same time, while the magnet was excited, the internal 

 resistance of the tube as measured by an alternative .spark gap 

 was found to be very greatly diminished. 



On demagnetising the magnet the appearance of the discharge 

 and the resistance of the tube immediately reverted to what they 

 had been previously. The effect was quite independent of the 

 polarity of magnet pole, and when the po.sition of the tube was 



