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 -3- III. Experimental Results and Conclusions. 3.0 Introduction.

In this section we shall describe the experimental results obtained and draw conclusions therefrom which bear upon the ultimate accuracy of the measurement of e/m. At this stage of the experiment, however, we had not as yet set up the apparatus for the precise measurements of voltage, frequency and length referred to at the end of 1.0. These results, therefore, will yield only estimates as to the resolving power of the instrument, and will permit estimates as to the ultimate accuracy of the actual e/m measurement when it is made.

3.1 Experimental Results--Current Peaks.

Typical measured current peaks, of the type predicted in section 1.7, are shown in Fig.17 and Fig. 18. It will be convenient in describing these curves to define the term "half-width" to mean the change in beam voltage necessary to reduce I/I0 from 1, its value at the synchronous voltage, to 0.5. It is essentially therefore, the familiar, "half width at half maximum."

It is clear from an inspection of Eq. 1.7,(1),&(2), that the shape of the current peaks depends on a large number of parameters. It must be remembered too, that the theoretical peak shapes derived in section 1.7 and shown in Fig.4, are based on an idealization of the current distribution in the beam. Actually, the beam does not have a uniform "disc" of intensity, but, rather, exhibits an umbra and penumbra, characteristic of the illumination of one hole through another. It is somewhat surprising therefore, that the agreement between the theoretical curve of Fig. 4