692 



Miss A. Muszkat on the /3?Recoil 



emanation. After the activation, the wire was heated in a 

 special apparatus in vacuo to remove the occluded emanation. 

 The 7-activity of the wire was then measured. Finally, after 

 RaAhad died off, the wire was introduced into the recoil vesse I 



the upper part occupying the central position. The pump 

 was set in movement, until the highest obtainable vacuum 

 (about 0*6 dyne/cm. 2 ) was reached. At this moment the 

 upper vessel was displaced and an electric current sent 

 through the platinum wire, heating it to a mean tempe- 

 rature of 426 C, as measured by the variation of its 

 resistance, controlled by means of an ampere- and voltmeter. 

 The current lasted for 1 minute, the cold disk (10 mm. in 

 diameter) being maintained 1 mm. above the wire. It is 

 worthy of notice that the temperature of the wire plays an 

 important role in the subsequent recoil phenomena. If it is 

 too low, the quantity of distilled matter is too small. On the 

 other hand, it is useless to raise the temperature considerably 

 above 426°, for although the disk B becomes more active, the 

 efficiency of the recoil is diminished and falls to a very low 

 value when the temperature is above 800°. This shows, as 



