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coincident with, or parallel to, the scale of i/io'" m. units, and 

 the positions of the various lines are set off on this scale {-ee Fig. 

 2) for the group, which is divided into four series. Ordinates 

 are then drawn in the position occupied by each line. The axis 

 of^ is divided into a number of equal parts, i, 2, 3, «. Lines 

 parallel to the axis of x, drawn from each of these divisions, in- 

 tersect the respective ordinate;. The continuous curve passing 

 through the points of intersection is found to possess all the pro- 

 perties of a parabola. 



Three points at least are selected to determine the position of 

 the vertex and value of latus rectum. The distance from the 

 origin along y is also found for an ordinate to the first line of a 

 series. 



Now, from the equation to the parabola y"=px, the formula 



= V + ^ 



is derived, where V = thewave-lengthini/io^''m. 



units of a point in the spectrum coinciding with the vertex of 

 the curve ; p, the latus rectum ; «. any number of units, reckon- 

 ing from the origin ; c, a constant. 



In practice a representation more suitable for lantern projec- 

 tion being desirable, two units are taken on^ for each line of 



the series ; the equation then becomes \ = V -h i-^ -V-, where 



1, = 4/, and c has twice its former value. 



April 20.—" Magnetic Viscosity." By J. Hopkinson, D.Sc, 

 F.R.S., E. Wilson, and F. Lydall. 



Income experiments carried out by Dr. J. Hopkinson and B. 

 Hopkinson, an account of which appeared in the Electrician of 

 September 9, 1892, it was found that 

 when hysteresis curves were obtained 

 for rings of soft iron and hard steel wire 

 hy means of alternate currents, and com- 

 pared with curves taken with the bal- 

 listic galvanometer, in the cases where 

 the induction wa? considerable, there 

 was a marked difference which might 

 be due to magnetic viscosity or to the 

 ballistic galvanometer. 



To settle this question the experi- 

 ment was tried of completing the gal- 

 vanometer circuit at known intervals 

 of time after the magnetising force 

 had been changed, and noting the 

 deflection. The effect of the self- 

 induction of the ring was approxim- 

 ately calculated, and found inadequate 

 to account for the deflections obtained. 



Next, the experiments previously 

 alluded to were continued, and curves 

 of hysteresis obtained with alternating 

 currents of a frequency of 5, 72, and 

 I2t) V per second, the method of pro- 

 cedure being exactly the same. In all 

 the curves thus obtained it was seen 

 that the more rapid the change of mag- 

 netising foice, the greater was the de- 

 viation from the curve taken »ith the 

 ballistic galvanometer. The accom- 

 panying figure gives the hysteresis 

 curves actually obtained, and show 

 this point very clearly. 



Similar experiments were carried out 

 on hardened chromium steel, and the 

 same effect was observed but was not so 

 marked. 



The following conclusions are drawn 

 from the experiments : — (i) As Prof. 

 Ewing has already observed, after 

 sudden change of magnetising force the 

 induction does not at once attain to its 



full value, but there is a slight in- 



crease going on for some seconds. (2) _||j^^^^^^^^_ 

 The small difference between the bal- 

 listic curve of magnetisation with 



complete cycles, and the curve determined with a considerable 

 frequency which has already been observed is a true time effect, 

 the difference being greater between a frequency of 72 v per 

 second and 5 v per second, than between 5 v per second and 

 the ballistic curve. 



fune I. — " On the Metallurgy of Lead." By J. B. Hannay. 

 Communicated by SirG. G. Stokes, F. R. S. 



In this paper the author deals with the result of seven years' 

 researches on the metallurgy of lead. 



It is shown that by repeated crystalli-iation any subsulphide 

 of lead may be fractionated into meta'lic lead, and its mono- 

 sulphide. The sp.gr. of pure monosulphide is found to be 

 7766, and the methods of analysis are reviewed and corrected. 



The reaction, PbS -I- PbS04 = 2Pb -(- 2SO.^. which was sup- 

 posed to explain lead smelting, is shown to have no existence, 

 as when lead sulphate and sulphide react upon each other, a 

 volatile compound, PbS.^OjOr PbS.SOj, is formed which intro- 

 duces complications, and being unknown to chemists was the 

 cause of the errors in the accepted furnace reactions of lead. 



This substance is formed whenever its constituents PbS, and 

 SO5, meet at high temperature, and is the cause of lead fume. 

 Similar volatile compounds are formed by the gases COj, CO 

 and II„0. These bodies dissociate on cooling, but form colour- 

 less gases at a red heat. 



All the furnace reactions of lead compounds are examined and 

 corrected in the light of these discoveries, and the fact applied 

 to explain the metallurgy of lead. 



A new metallurgy is mapped out by which galena is treated 

 in a Bessemer converter, and made into pig-lead, litharge, or 

 sulphate of lead, in any proportions as may be desired, while all 

 the silver is eliminated. 



" Flame Spectra at High Temperatures. Part I. Oxy- 

 hydrogen Blowpipe Spectra. " By W. N, Hartley, F. R.S. 



The substances examined are supported in the oxyhydrogen 



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flame on small plates of kyanite. This mineral contains ninety- 

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