A. C. REDFIELD AND E. M. BRIGHT 33 



Procedure. 



Homogeneous groups of /3-rays have been procured by the method 

 commonly used by physicists, which depends on the fact that in 

 traversing a magnetic field these negatively charged bodies are de- 

 flected in a direction normal to the field and as a consequence travel 

 in curved paths. The relation between the velocity of a /S-particle, 

 w, the radius of curvature of its path, R, and the strength of the 

 magnetic field, H, are given by the equation 



m u 



HR = 



e 



where m is the mass of the particle and e its charge. For our purpose 

 it will sufiice to note that the relative velocity of the /3-ray is meas- 

 ured by HR, the product of the radius of curvature and the strength 

 of the magnetic field, which are predetermined experimental con- 

 ditions. By making the usual assumptions concerning the value of 

 e and of m for various velocities absolute values might be assigned 

 to the velocities of the beams of /3-rays which we have used. 



The apparatus which we have employed is illustrated in Fig. 1. 

 A solenoid, 50 cm. long, was wound about a hollow water jacket, 

 WJ. Knowing the number of turns of wire in the solenoid, its 

 length, radius, and the strength of current passing through it, the 

 strength of the magnetic field, H, in its center could be calculated 

 directly. A stream of water circulating through the water jacket 

 prevented the heat generated in the solenoid from increasing the 

 temperature of the space within. Into this space could be introduced 

 an arrangement for exposing the eggs to rays separated into homo- 

 geneous groups by the magnetic field. This device consisted of two 

 lead blocks so arranged that a slender glass tube containing radium 

 emanation, E, was supported 1 cm. from a slit, S, through which a 

 beam of rays escaped. » The width of the slit was 0.1 cm. in some 

 experiments, 0.065 cm. in others. When undeflected, the rays leav- 



^ We are greatly indebted to Dr. William Duane for indispensable advice in de- 

 signing our apparatus, and to Dr. R. B. Greenough, the Director of the Cancer 

 Commission of Harvard University, for placing a supply of radium emanation at 

 our disposal. 



