Radio-activity ami the Electro* Theory. 



417 



distance, retains its property of communicating radio-activity to other 

 bodies. He explains these phenomena by supposing that thoria gives 

 oft' a special kind of emanation capable of being conveyed by the air, 

 and that this is the cause of the induced radio-activity. 



To ascertain if the electrons or corpuscles from radium also possess 

 the property of being carried along in a current of air, I fitted up an 

 apparatus shown in fig. 2. A, B, and C are three brass tubes closed 



y ^//////////^^^^^ 



FIG. 2. Elevation. 



at the lower end and cemented with paraffin to a wooden block. The 

 upper ends were accurately ground to a level surface, and then coated 

 with a thin layer of paraffin wax. Holes were drilled in B and C, to 

 admit glass tubes, cemented air-tight into the cylinders, as shown in 

 the figure. The upper end of the tube in B was closed with a plug of 

 cotton wool, and the outer end in C was connected to a water-pump, 

 so that when the cylinders were closed at the top a current of air was 

 drawn through B and C. As the radium compound was self-luminous, 

 discs of thin aluminium foil were placed over cylinders A and B to cut 

 off the luminous rays. A sensitive film was laid on the three cylinders 

 over the aluminium, and it was tightly pressed down by a heavy weight ; 

 the contact between the film and the tops of the cylinders being suffi- 

 cient to make the whole air-tight. At the bottom of A and B a radium 

 compound was placed, equal weights and equal surface in each. The 

 whole was put into a light-tight box, and air drawn through. The 

 cylinder A was used only as a standard. The air passing into B was 

 expected to carry along with it some of the corpuscles emitted from 

 the active material at the bottom ; and the inlet tube in C was turned 

 up at the end, so that the stream of corpuscles-laden air should impinge 

 on the surface of the centre of the film on C, and if it carried with it 

 any radio-active properties the result should be seen on development, 



