2nd APPEARANCE IN PRINT OF TWO IMPORTANT PAPERS, FLEMING ON HIS VALVE & BARKLA’S 1st IN-DEPTH PAPER SHOWING THAT X-RAYS SCATTERED BY VARIOUS ELEMENTS PRODUCED BEAMS OF CHARACTERISTIC PENETRATION.
Both papers were first read before The Physical Society of London on 23 March 1906; each was then printed in the July 1906 edition of The Proceedings of The Physical Society of London. Following that publication, they appeared in the volume offered here, the 1906 Phil Mag.
NOTE: We separately offer the first printed edition, papers the July 1906 edition of Proceedings of The Physical Society of London in original wraps and inclusive of both papers.
In 1904, J. A. Fleming rectified wireless signals using a diode based on the Edison effect, the unilateral flow of current between two electrodes in a vacuum tube; this was the first known use of the Edison effect. Fleming called his invention an "oscillation valve" because it acted in similarly to a valve in a pump that allows gas or water to move in only one direction. Fleming had “discovered that thermionic emission could be used to create what is now called a thermionic or vacuum tube, a device that controls the flow of electric current. He patented the vacuum tube as a rectifier to replace the coherer for use in receiving wireless transmissions” (Wenner Collection).
In reading his work at the Physical Society, Fleming “outline[d] the design and use of devices for rectifying high-frequency oscillatory signals such ‘as are employed in the rectifying circuits of wireless telegraph apparatus’” (Davis, Science, 8). “Oscillations in the primary circuit, produced by an induction coil and two Leyden jars, generate Hertz waves which are detected some distance away by the secondary circuit. The valve rectifies this signal, as confirmed by the steady deflection of a mirror galvanometer. Fleming used this arrangement to investigate the effects of changing various features; he also experimented with different filaments in the valve (ibid). Fleming’s discovery “was later developed by others for a host of applications from sound amplification to electronic switching in digital computers” (ibid).
BARKLA: The English physicist began investigating Roentgen’s newly discovered X-rays while at Edinburgh. “Barkla noticed that X-rays were scattered by gases and that the degree of scattering was proportional to the density and molecular weight of such gases. From these, he deduced that the more massive the atom, the greater the number of charged particles in the nucleus and the degree of scattering.
“This was the first time that a connection was made between the number of protons, the atomic weight and the position of an element in Mendeleev’s periodic table. This was definitely a move toward the development of the concept of the atomic number and the recognition of its importance in the ordering of the chemical elements in the periodic table” (Martini, The Story, 690). By 1905, Barkla could clearly distinguish “between the properties of secondary radiation from heavy elements and those of the scattered radiation by lighter elements” (Authier, Early Days, 5.7).
Here Barkla does “his most intuitive thinking, [showing] that X-rays scattered by various elements produced beams of characteristic penetration. This was indicated by the degree of beam absorption by an aluminum sheet of standard thickness. At that time, there was no way to measure the wavelength of X-rays; therefore, Barkla had to make his assessment by the absorption on the aluminum sheet” (Martini, 690). Barkla was awarded the 1917 Nobel Prize; his discovery was later used by Henry Moseley to show that elements can be uniquely represented by their ‘atomic number,’ the charge of the nucleus. Item #819
CONDITION: Complete. Ex-libris: blind (uninked) stamp on title page; no other markings. Tightly bound three quarter calf; minor scuffing at tips. 5 gilt-tooled bands at the spine. Gilt red and black morocco spine labels. Bright, clean, very good.