Boston, Massachusetts: Prang Educational Company [ 1882-1897 ]. Inside the frame edge is 9 3/4 x 39 3/4 inches. Frame dimensions are somewhat larger. Chart labeled "Prang's Prismatic Spectrum | with the Frauenhofer Lines | The Space Values of the Colors in this Spectrum are based upon measurements given by Prof. Ogden N. Rood of Columbia College, New York." above the illustration. "Published by the Prang Educational Company, Boston, MA U.S.A." bottom center, and "Lith by L. Prang & Co." lower left. There is a small label on the frame as well, and a small amount of surface wear to the spectrum. Overall nice and clean, something carefully preserved given that the classroom environment was it's likely home. Glass missing, with several small nicks to the color chart. Very Good. 
This didactic chart illustrates what happens when light from a source like the sun is projected through a prism and broken up into it's constituent parts. The result is a continuous light spectrum which we see as colors much like an expanded rainbow. Scientist Joseph von Fraunhofer discovered that when properly projected one could also see "absorption lines" which appeared as dark lines in this spectrum, each of which had characteristic points (or wavelengths) in the spectrum. This discovery allowed the experimenter to help determine what elements were present in the source of the light thus viewed. It turns out this is very useful in astronomy and other scientific fields interested in understanding the composition of unknown materials.
The observant reader will note that this chart doesn't actually show any Fraunhofer lines (which would be darker) but merely the locations of some standard, known lines. We believe this is by design (a teachable moment), as a poorly designed experiment without a slit and focusing mechanism in the correct place in the light path would create just this sort of spectrum (continuous and lacking any Fraunhofer lines). With the addition of a properly sized slit through which the light is projected, and a focusing mechanism, the lines would indeed appear at their proper locations as noted to the sides of the chart, proving the teacher's hypothesis and creating an aha moment for students.
Louis Prang established L. Prang & Co in 1860, initially publishing greeting cards, civil war ephemera, and novelty items. After a trip to Europe in 1864 to study German lithographic techniques, Prang returned to the Boston area doing work with "chromos". By 1874 he was producing excellent Christmas cards, and also "began publishing books for drawing and elementary art study for public schools." This was so successful that he started the Prang Educational Company in 1882. L. Prang & Co merged with another company and became the Taber-Prang Company in 1897, moving to Springfield, MA.
Scarce, with only a few examples we've seen over 20 years. The Harvard University Collection of Historical Scientific Instruments has an example whose inventory notes: "This instrument is found in Hugo Münsterberg's 1893 Psychological Laboratory of Harvard University document. It is thus listed: "103. Prismatic spectrum charts in frame. By Prang, Boston. $5.""
History derived from the Smithsonian Institute's Louis Prang papers, 1848-1932 Biographical Note.