. The London, Edinburgh and Dublin philosophical magazine and journal of science. rection in the plane of xzyinclined to z (towards a) at a small angle 6, such that 6=-KAK-1S-2 = ^S2. . (61) 15 K 15* In the usual case of particles optically denser than the sur-rounding medium, AK is positive, from which we gather thatthe direction in which the scattered light vanishes to the secondorder of approximation isinclined backwards, so thatthe angle through whichthe light may be supposedto be bent by the actionof the particle is obtuse. The fact that, when theprimary light is polarized,there is in one
. The London, Edinburgh and Dublin philosophical magazine and journal of science. rection in the plane of xzyinclined to z (towards a) at a small angle 6, such that 6=-KAK-1S-2 = ^S2. . (61) 15 K 15* In the usual case of particles optically denser than the sur-rounding medium, AK is positive, from which we gather thatthe direction in which the scattered light vanishes to the secondorder of approximation isinclined backwards, so thatthe angle through whichthe light may be supposedto be bent by the actionof the particle is obtuse. The fact that, when theprimary light is polarized,there is in one perpendi-cular direction no lightscattered by very smallparticles, was stated byStokes*; but it is, I believe, to Tyndall that we owe the obser-vation that with somewhat larger particles the direction ofminimum illumination becomes oblique. I do not find, how-ever, any record of the direction of the obliquity (that is, ofthe sign of the small angle 6), and have therefore made a fewobservations for my own satisfaction. In a darkened room a beam of sunlight was concentrated. * Phil. Trans. 1852, § 183. 96 Lord Rayleigh on the by a large lens of 2 or 3 feet focus; and in the path of the lightwas placed a beaker glass, containing a dilute solution of hy-posulphite of soda. On the addition of a small quantity ofdilute sulphuric acid a precipitate of sulphur slowly forms,and during its growth manifests exceedingly well the pheno-mena under consideration. The more dilute the solutions, theslower is the progress of the precipitation. A strength suchthat there is a delay of four or five minutes before any effectis apparent, will be found suitable; but no great nicety of ad-justment is necessary. By addition of ammonia in sufficientquantity to neutralize the acid, the precipitation may bearrested at any desired stage. More time is thus obtained tocomplete the examination ; but the condition of things is notabsolutely permanent, the already precipitated sulphur appear-ing to aggregate i
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