She said that this showed that the alpha particles were not scattered, that is, able to be bent from their path. They were wrong. Becquerel, using his different techniques, checks and confirms Rutherford's results. Of course, with no magnetic field, he gets a nice, crisp image of the narrow slit, directly in line with the radium source. When he turned on the magnetic field, he got Rutherford's result, that is, the alpha particles bent in the magnetic field.
Part b of the figure shows the offset of the image on the photographic plate.
It is not lined up directly with the open slit, labeled Y. Becquerel also reversed the magentic field's direction during the exposure and got a double image. Up to this point, there was zero evidence of alpha particle scattering. Now, the evidence starts to accumulate The work described above was all done in the early part of 1903 and it was in June of 1903 that Becquerel made the first observation that led to alpha particle scattering. It seemed that the radius of curvature of the alpha particles path through the slit Y increased as b increased, thereby moving the two images closer together. What Becquerel did is assume E is constant, so this left him with the unpleasant thought that either v or M had to increase.