Pear Shaped Crookes Tube

                   Instead of having the electrodes “in line” on the opposite sides of the tube, as in the early Crookes tube, the cathode is a flat aluminum plate on the narrow side of the “pear” while the anode is “rod shaped” in a secondary lateral tubular chamber on the larger side. The other tubular extension is for the vacuum

                  It is while experimenting with a similar tube that Röntgen incidentally discovered X-Rays late in 1895. These rays, of an unknown nature yet, were produced by a large area of the glass wall on the larger side of the tube, by the impact of the unfocused “cathode rays” (electron beam). This large size of the x-ray source  accounts for the unsharpness of the earliest x-ray “photographs”.

                  Such tubes were soon abandoned for the production of X-rays, and replaced by what came to be known as “the focus tube”.