40 



The Eadium Clock. 



By R. R. Ramsey. 



R. .T. Stntt (Fhil. 'Slag. G, 588, 1903) has devised a very simple little 

 device to show tliat a radium preparation takes on a positive charge due 

 to the P.-r.-iys. This consists of a radiiim iirei;aration enclosid in a thin 

 walled glass tube. The tube is suspended in a vacuum tube by means 

 of a quartz rod. To the lower end of the tube a gold leaf is suspended, 

 forming an electroscope. The B-rays cause the tube to become positively 

 charged, the L-rays being absorbed by the glass, the leaves diverge, and 

 if the gold leaf is allowed to touch an earthed plate the charge is taken 

 off and the process of charging begins over again with a regularity which 

 suggests perpetual motion. The term radium clock has been suggested by 

 some one as a name for the device. It was the original intention to ex- 

 hibit one here today. 



The only successful one which I have been able to make is the one I 

 had when the title was sent in. Since the period of this one is about 48 

 hours, I have concluded your faith would be tried as much with the 

 exhibit as without. However, the tube is on the table. It was my hope 

 to be able to make one in a neat, short tube with a quick period which 

 could be used in front of a lantern. To accomplish this .50 mg. of 10,000 

 activity radium was placed in the tube. The quartz was discarded and 

 the tube set upon a block of hard rubber in the l)ottom of a test tube, 

 with the gold leaf hanging alongside of the radium tul>e. When ex- 

 hibited to a vacuum of lower pressure than my first tube, the gold leaf 

 refused to move. The tube was prepared again with a quartz rod be- 

 tween the tube and the hard rubber. This also failed to work. Since 

 the gold foil hung alongside the I'adium the li-rays were partially ab- 

 sorbed by the gold, thus neutralized the charge. At the last moment I 

 was forced to come back to the original form. This has failed to work, 

 probably due to dirt on the quartz rod. The essentials for success are 

 plenty of high activity radium, thin glass, containing tube hermetically 

 sealed, perfect insulation and a good mercury pump. 



