The
Focus Tube (1896)
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This type of tube, introduced in 1896, a few months
after Röntgen’s discovery of X-rays, is commonly
known as the JACKSON TUBE or Focus Tube. In the above pictures, the tube is
seen from different angles. The
anti-cathode is a very thin square plate of pure platinum. Etched on the
back-side of the aluminium cathode are the maker’s
name and address “ Hereafter is an early description of this tube : …..The
most important step in the evolution of X-Ray tubes is marked by what is now
commonly called the focus tube. The credit of its inception is given to three
different investigators, namely, Prof. Röntgen
himself, Prof. Elihu Thomson who is said to have
worked with a focus tube in January, 1896, and Mr. Herbert Jackson, of King’s
College, London, who, at any rate was the first to use it
publicly…….The design of the focus tube obviates the defects of
cathode tubes, in so far as the point which the cathode rays strike is no
longer the glass of the tube, but a suitable metal (platinum) which may
become white hot without endangering
the tube itself. Moreover, as the cathode is of concave shape, the cathode
rays converge to a focus, so that the source of x-rays becomes limited in
size and so permits of superior definition in the resulting radiograms. ….. In
later types, particularly of continental origin, the tube is provided with a
separate anode which may at will be connected to the anticathode. Several
forms of “multi-anodal” tubes are illustrated
(A.W. Isenthal and
H. Snowden Ward –“Practical Radiography”, 1898, p.57 and p.60)
I am deeply indebted to
Dr. Paul Frame, of Oak Ridge Associated Universities, for having this
tube in this collection. collection |
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