. American X-ray journal . rate, within a mod-erate distance, but continues in a thinline. It is when this stage of exhaus-tion is reached that Roentgen rays aregiven off in their most active and mostpenetrative form. Experiments showthat both the convergent and divergent THE AMERICAN X-RAY JOURNAL. 303 cones of cathode rays are hollow, andnot solid in section. When the concen-trated cathode rays are allowed to fallupon a disc of ordinary electric lightcarbon, the latter exhibits surface lu-minescence. Except, however, whenthe disc is exactly at the focus, in whichcase it shows a bright lumino
. American X-ray journal . rate, within a mod-erate distance, but continues in a thinline. It is when this stage of exhaus-tion is reached that Roentgen rays aregiven off in their most active and mostpenetrative form. Experiments showthat both the convergent and divergent THE AMERICAN X-RAY JOURNAL. 303 cones of cathode rays are hollow, andnot solid in section. When the concen-trated cathode rays are allowed to fallupon a disc of ordinary electric lightcarbon, the latter exhibits surface lu-minescence. Except, however, whenthe disc is exactly at the focus, in whichcase it shows a bright luminous spot,the intersection of either cone by thedisc gives not a solid spot of lumin-escence, but a hollow luminous ring,which decreases in diameter the higherthe exhaustion, as shown in the lowerportion of Figs. 1 to 4. It appears. figs. 1, 2, 3 and 4. further that the cathode rays are notgiven off from the whole surface of thecathode cup, but only from a ring-shapedportion, the diameter of which is lessand less the higher the , perhaps, explains the reason whyvery large cathodes give no better re-sults in producing x-rays than compara-tively small cathodes. Indeed, at thedegrees of vacuum necessary to producepenetrative x-rays, the greater portionof a very large cathode is apparently in-effective, as the discharge seems to comeoff entirely from a very small part of thecentral portion. This is not readily seen with the usual cathode cups of alu-minum, but with cups of carbon it iseasily observed. Full details of the ex-periments from which the above factsare derived, will be found in The Pro-ceedings of the Royal Society, , pages 79 to 95. Cathode rays are generally believedin this country to consist of atoms ofmolecules of residual gas, which beingsimilarly electrified to the cathode, are
Size: 1682px × 1485px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectrad, booksubjectxrays
