292 Prof. "Richardson and Lieut. Bazzoni on the 



A is an ammeter reading to 1/30 ampere, T a Dolezalek 

 electrometer sensitive to 600 divisions per volt. The 

 currents in the field coils were read from an Elliot standard 

 ammeter to 1/20 ampere, and checked against the readings 

 of a second ammeter in the circuit of the compensating coil. 

 The 400 volt battery was made up of small storage-cells. 

 The other batteries, as well as an auxiliary battery giving up 

 to 1000 volts, were composed of dry cells. 



We shall now consider briefly the action of the apparatus. 

 When in use electrons are accelerated across from the fila- 

 ment to one or other or both of the anodes under a known 

 potential. The electrons strike the gas atoms and, if of 

 sufficient energy, directly or indirectly cause the liberation 

 of radiation from them which will, speaking generally, con- 

 stitute an entire spectrum. This heterogeneous radiation 

 passes between the guard plates and strikes on all parts of 

 the target in the copper cylinder, liberating electrons from 

 it with a great variety of velocities and in all directions. 

 The electrons which come out normally will travel in circles 

 under the influence of the magnetic field, and all of those 

 moving in circles the radii of which end in the slits will 

 arrive in the terminal cup and cause a deflexion of the 

 electrometer. It is seen then that for every setting of the 

 magnetic field the presence of electrons between certain 

 velocity limits will be recorded by the electrometer. The 

 finite size of the slits exerts a further influence in that 

 electrons which come out of the target in directions inclined 

 a certain amount to the normal both vertically and horizont- 

 ally, will also pass through the slits in quantities depending 

 on their place of origin on the t?.rget and on their angle of 

 emission. This effect is a maximum for the central part of 

 the target. The distribution of energy received at the cup 

 for any particular field as determined by graphical methods * 

 is shown in fig. 3 A for a plane across the slit and perpendi- 

 cular to it. In the calculations for these figures the slit 

 width is taken for the sake of convenience to be 2 mm. The 

 distribution has also been contoured in the other perpendicular 

 plane due to the height of the slit admitting screw-motion 

 electrons. Fig. 3 B represents the final distribution taking- 

 account of both of these effects. The horizontal coordinate 

 in both of these curves is the radius of the electron path — 

 the radius at the centre of the slits being 5 mm. This curve 

 shows that for any particular setting the main part of the 



* Cf. Ramsauer, Sitz. der Heidelberger Akad. d. Wiss, 19 Abh. p. 8 

 (1914). 



