- The Pennsylvanian (/ˌpɛnsəlˈveɪni.ən/ pen-səl-VAYN-i-ən, also known as Upper Carboniferous or Late Carboniferous) is, on the ICS geologic timescale, the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. It lasted from roughly 323.2 million years ago to 298.9 million years ago. As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain by a few hundred thousand years. The Pennsylvanian is named after the U.S. state of Pennsylvania, where the coal-producing beds of this age are widespread.
- J. J. Thomson and The Electron: 1897–1899: An Introduction (PDF)
This being the 100th anniversary of J. J. Thomson’s discovery of the electron, the October 1897 paper in which he presented his case that cathode rays are streams of subatomic “corpuscles” is attracting a great deal of attention. Viewed from 100 years later, this paper stands out as the starting point for the research into the structure of the atom that has dominated 20th-century science.