CONTEMPORARY ADVANCES IN PHYSICS 



115 



moments, but the felicitous law of the equality of the intervals makes 

 all easy — all that is needed is to connect an oscillator of the proper 

 frequency (determined by the strength of the magnetic field and the 

 charge and mass of the ions) across the pair of half-boxes. ^'^ 



Fig. 4 — Photograph of the apparatus sketched in Fig. 3. (E. O. Lawrence) 



The sketch of Fig. 3 is of the apparatus wherewith Henderson 

 observed the transmutation of lithium by protons (pp. 140-142). 

 It is filled with hydrogen of a low density, so that electrons proceeding 

 from the hot filament F at the center ionize the gas and produce a 

 sufficient number of protons. These are whirled around and around 

 in ever-widening semicircles, till after a number of circuits which may 

 be as high as one hundred and fifty they arrive at the boundary of the 



^^ One may do without the magnetic field, arranging to have the ions proceed along 

 a straight line and to accelerate them at definite points along that line, by voltages 

 produced in rhythm by an oscillator; the points of application of the voltages must be 

 spaced according to a particular way, and the apparatus is inconveniently long, being 

 longer the lighter the ion; it has been successfully employed with mercury ions by 

 Lawrence and some of his colleagues. 



