2S4: Mr. Norman Campbell on Delta Rays. 



of the current for the same difference of potential when the 

 apparatus was introduced into a magnetic field so strong that 

 a further increase in it produced no change in the current. 

 The next nine rows give the form of the curve, exemplified 

 by fig. 1, which is plotted from column 6. The fourth row 

 gives the absolute value of tbe maximum ordinate QD or 

 Q'O, the former being placed in the column marked +, the 

 latter in the column marked — . The eight rows immediately 

 be'ow the double horizontal line give the values of the ordinates 

 PN or P'N' corresponding to values of V denoted in the 

 first column ; those in tbe column marked + denote the 

 values when B is positive to A, those in the column marked — 

 those when B is negative to A. In order to enable a com- 

 parison to be made between d fferent columns the values are 

 not expressed in absolute measure, but as fractions of the 

 maximum ordinate. The absolute value in any case can be 

 found by multiplying the number recorded by the number 

 in the same column immediately above the thick line. The 

 last two rows will be referred to later. 



9. According to § 3 the columns marked + refer to the pro- 

 perties of the rays emitted by B, those marked — refer to the 

 properties of the rays emitted by A. In accordance with the 

 nomenclature introduced by Prof. Bragg, we may call these 

 rays respectively " emergence " and " incidence " radiation. 

 The first point which needs inquiry is the relation between the 

 inciJence and emergence radiations, it will be noted that 

 the amount of the emergence radiation, given by the fourth 

 row ( -f column), is never greater than the amount of the 

 incidence radiation (— column) ; when the layer through 

 which the rays emerge is very thin the emergent and inci- 

 dent radiations appear to be equal, while, as that layer 

 increases in thickness, the emergent radiation decreases re- 

 latively to the incident. The ratios of the emergent to the 

 incident radiation are given in the tenth row; it will be seen 

 that this ratio appears to be constant after a certain thickness 

 of the layer is reached. Columns 7 and 9 are somewhat 

 anomalous, but there are other indications that column 7 is 

 affected by some source of error, while the current dealt 

 with in column 9 is so small that the apparently large diver- 

 gence of the ratio is not really greater than the possible error 

 of observation. 



This result is certainly surprising and difficult to explain. 

 Further investigation of the point is certainly necessary. 

 But it may be noted that in all the experiments described in 

 this paper, and in a large number of preliminary observa- 

 tions with different apparatus, of which the results are not 



