In 1888 the Hungarian Philipp Lenard (1862-1947), assistant to George Quincke at Heidelberg, on having the possibility of constructing a mercury pump for the creation of extreme vacuums, began his studies of cathode rays. He believed that it would be easier to observe and analyze them outside the tube by closing it on the side opposite the cathode with an air-tight window that allowed the cathode rays to pass; but, on using a quartz window 2.4 mm thick, he observed no electric, magnetic fluorescent or phosphorescent effect at all.
In 1892 Einrich Hertz (1857-1894) a professor at Bonn, showed Lenard, who was his assistant, that on introducing into the tube a piece of lead glass wrapped in aluminium foil, when the cathode rays struck the aluminium the glass became fluorescent. Transparency with cathode rays had been observed by Hertz also with gold and silver leaf of the kinds used by bookbinders.
Later, Lenard introduced sheets of aluminium foil one after the other into a tube prepared specifically for the purpose; as the number gradually increased, he established that up to 10 or 15 sheets were sufficiently transparent to cathode rays.
He then took a lamina of aluminium of the same consistency, replaced the quartz window in the old tube with one of perforated metal and covered the hole with the strip of aluminium; on exciting the discharge in the tube he could observe on the outside, near the hole, the phosphorescence of grains of an alkaline substance.
These cathode rays coming out of the tube were given the name of Lenard rays.
On using a specially-built tube and passing it through a recipient containing different gases at different pressures, Lenard was able to study carefully the properties and effects of cathode rays and make the following observations:
1) at atmospheric pressure, in air the rays produce fluorescence and impress photographic plates up to a distance of about 6 cm from the aluminium window, while in carbon dioxide they reach 4 cm and in hydrogen 30 cm;
2) the absorbing power depends not so much on the nature as on the density of the material penetrated; at the same thickness, gold absorbs cathode rays more than does silver and aluminium.
In 1905 Lenard received the Nobel Prize for Physics "for his work on cathode rays".
The tube in the museum collection is made of glass painted black on the outside. It consists of two cylindrical parts, the axes of which are orthogonal to each other; one is 22 cm in length and the other is 20 cm long.
The former consists of two coaxial parts of different lengths joined together; the cathode which is a small aluminium disk attached at the centre to a small rod, it too made of aluminium,, is placed near the middle of the narrowest part (length 10 cm, diameter 1.4 cm); the disk is connected to the outside by means of a wire welded to the glass at the extremity of the tube; in the widest part (diameter 3 cm) the tube is sealed with a metal disk with 25 holes with a diameter of a few tenths of a millimeter covered with a thin piece of aluminium. One of the holes is at the centre and the others are placed symmetrically around it within a diameter of 3 mm.
The other part of the tube is welded to the first part at about 5 cm from the metal disk and terminates with a joint having the shape of a truncated cone for connection to the vacuum pump; near the middle, in an appendage perpendicular to its axis, we find the anode.
Heathcote (1953), p. 34 e seg.
Murani (1906), Vol. II, p. 627
Roiti (1914), Vol. II, p. 564