The ordinates represent the distance between the radium and the gauze of the testing vessel; the abscissae the current in the ionization vessel in arbitrary units. Five milligrams of radium bromide were used, and the depth of the ionization vessel was about 5 mms. Curve _A_ is for a cone of rays of angle 20°. The initial current at a distance of 7 cms. is due to the β and γ rays and natural leak. This curve is initially parabolic, and then is made up of two straight lines. Curve _B_ is for a smaller cone, and shows the straight line character of the curve to within a short distance of the radium. Curve _C_ was obtained under the same condition as curve _A_, but with a layer of gold beater’s skin placed over the radium. The effect of this is to reduce all the ordinates of curve _A_ by the same quantity. This is to be expected on the simple theory already considered. Curve _D_ was obtained when the radium was heated so as to get rid of the emanation and its products. The α particles of greatest range are quite absent and the curve is simpler in character. [Illustration: Fig. 42.] The complex character of the radium curves are more clearly brought out by a careful examination of a portion of the curve at distances between 2 and 5 cms. from the radium, using an ionization vessel of depth only 2 mms. The results are shown in Fig. 42, where the curve is seen to consist approximately of four straight lines of different slopes represented by _PQ_, _QR_, _RS_, _ST_. Such a result is to be expected, for it will be shown later that four distinct α ray products exist in radium when in radio-active equilibrium. Each of these products of radium emits an equal number of α particles per second, but the range of each is different. If _a₁_ is the range of one stream, _a₂_ of another, the ionization in the vessel _AB_, when two streams enter the vessel, should be _nb_ _nb_ ---- (_a₁_-_h_-_b_/2) + ----- (_a₂_ − _h_ − _b_/2), ρ ρ _i.e._ _nb_ ---- (_a₁_ + _a₂_ − 2_h_ − _b_) . ρ Thus the slope of the curve should in this case be 2_nb_/ρ, while if only one stream enters, it should be _nb_/ρ. When three reach it, the slope should be 3_nb_/ρ and for four 4_nb_/ρ. These results are realized fairly closely in practice. The curve (Fig. 42) consists of four parts, whose slopes are in the proportion 16, 34, 45, 65, _i.e._ very nearly in the ratio 1, 2, 3, 4.