“These are some of the problems in connection with the sun which are being investigated at the present time. Their complete solution will help to interpret the mystery, not only of the sun itself, but also of that type of stars of which the sun is a representative.”
―Frederick Slocum, The Study of Solar Prominences. Popular Astronomy, July 12, 1912.
Frederick Slocum (Brown University undergraduate class of 1895) received the first Ph.D. in astronomy at Brown in 1898 and served as assistant professor of astronomy from 1899 to 1909. He then became professor of astronomy at Wesleyan University in 1914 where he planned and supervised the construction of Van Vleck Observatory. The image below shows Slocum observing with a spectroscope attached to the main telescope at Ladd Observatory.
This spectroscope was made by the scientific instrument maker John Brashear of Pittsburgh in 1891. It is used to study the spectrum of colors in starlight. It could also be mounted on a table top to examine the spectrum of a chemical which is done to calibrate the instrument. During this era professor Winslow Upton used it in an attempt to predict rain. It uses a prism or diffraction grating to disperse the light into a rainbow pattern of colors. This reveals dark Fraunhofer lines in the spectrum that can be used to identify the chemical elements present in the Sun or a distant star. Each chemical element has a unique pattern of these dark lines where specific colors are missing.
Another spectroscope at Ladd Observatory was made by Otto Toepfer of Potsdam in 1895. It is designed for high resolution studies of the solar spectrum. Slocum used this instrument to study features on the Sun including solar prominences. He writes that observations with this instrument could help him unravel some of the mysteries of our Sun and distant stars that are similar to it.
“By studying the shapes and bodily motions of the quiescent or cloud-like prominences, some insight may be gained into the general system of vertical and horizontal circulation of the solar atmosphere, that invisible medium in which the prominences float.”
Slocum and Upton traveled to Centreville Virginia to observe the solar eclipse of May 28, 1900. Slocum used a portable type of spectroscope called a prismatic camera to photograph the spectrum of the Sun. The spectrum above was taken during this expedition. Upton described their results in the Astrophysical Journal.
“Many lines are upon the plates, both dark and reversed, and the chief chromospheric lines are prominent. A faint continuous spectrum was obtained during totality.”