Martin D. Altschuler, “Atmospheric Electricity and Plasma Interpretations of
UFOs,” in Daniel S. Gilmore, ed.,
Scientific Study of Unidentified Flying Objects (New York; Bantam Books, 1969), 1164-1172. Available from: http://www.ncas.org/condon/text/s6chap07.htm#s7.
Additional information regarding ball lightning and its various properties from: http://amasci.com/tesla/ballgtn.htm. In 2012, Chinese scientists were observing lightning with a simple video camera paired with a spectrometer and inadvertently recorded the first natural occurrence of ball lightning:
"First instance of ball lightning captured on video and spectrographs" at Phys.Org (17 Jan. 2014): http://phys.org/news/2014-01-instance-ball-lightning-captured-video.html.