170 Mr Richardson, On an attempt to detect radiation, etc. 



the first. The wire was supported by sealing-wax both where it 

 entered and where it left the tube. The other end of the tube 

 was closed by a tight india-rubber stopper which could be removed 

 to insert the plates. The outside of the tube was painted with 

 several layers of black paint so that no light could get through. 

 After getting rid of troublesome glows no photographic action 

 could be detected. It was therefore concluded that no photo- 

 graphically active radiation was shot off at right angles to the 

 wire. 



In this apparatus there was no ver}^ ready means of discover- 

 ing whether the discharge really passed through the part of the 

 wire which was tested or not ; although it could be proved to be 

 passing through the parts of the wire external to the glass 

 apparatus by the insertion of a coil with an electrodeless discharge 

 bulb or of a spark gap. This defect was remedied in the form of 

 apparatus described below by the insertion of a mercury cup into 

 which the excited wire dipped, within the exhausted vessel. The 

 wire could be drawn at will out of the mercury and a spark gap 

 thus produced. By observing the light from the spark the inten- 

 sity of the discharge could therefore be determined. 



It was possible that although the ions did not move off at right 

 angles to the wire they might still be produced close to the 

 surface and pursue straight paths backwards and forwards parallel 

 to the wire under the influence of the electric field. In this case 

 the application of a strong enough transverse magnetic field 

 would cause them to move away from the wire, so that a photo- 

 graphic effect might still be got if the wire were placed in a 

 magnetic field. To accomplish this the wire was fixed axially in 

 a narrow glass tube, which was placed between the poles of an 

 electromagnet. 



The apparatus finally took the form shown in figure 1. The 

 discharge wire passed through the top of a T-tube, the top being 

 about 30 cms. long and '6 cms. diameter. The limb of the T-tube 

 was cut off about 1 cm. from the shoulder and inserted into the 

 cork e, so that it opened into the inside of a wide test-tube f 

 which was cut off about 12 cms. from the open end. Another 

 tube g also passed through the cork to the water-pump and mano- 

 meter used before. The limb of the T-piece only penetrated 

 half-way through the cork which was cut out so that the end of 

 the tube was flush with the surface. This enabled the photo- 

 graphic plates, which were fixed by soft wax on to the end of the 

 support d, to be brought as near the discharge wire as possible. 

 The tight india-rubber stopper h allowed of the removal of the 

 plates, while the other end of the tube was made air-tight by 

 covering the cork etc. with sealing-wax. The central wire was 

 free except for being fixed air-tight in a with sealing-wax. A was 



