Lommel's Optics

Abstract

I AM indebted to Prof. W. N. Hartley for a correction in my review of Lommel's Optics, the proof-sheets of which did not reach me in time for revision. The translator of the work is evidently right in using the term napthalin red for the body which exhibits the fluorescent spectrum depicted in Fig. 6 in the article. The substance in question, Prof. Hartley states, is also called Magdala red, and has the elegant chemical name of Azotrinaphthyldiamine. I am also obliged to my friend Prof. H. M'Leod for pointing out that the mode of exhibiting the formation of the rainbow described by Prof. Lommel, is to be found in Jamin's “Cours de Physique” (tome 2, p. 782), although the substitution of a spherical flask filled with water for a solid glass globe, as described by Jamin, is more appropriate and convenient. Pouillet (tome 2, p. 769) also gives, I see, a somewhat similar experiment, using a cylindrical glass vessel filled with water.