Prof. Tyndall on the White Rainbow. 149 



keenest interest the weird phenomenon before us, my wife 

 suddenly announced that she saw the bow continued to a circle 

 at her feet. Almost at the same moment, I saw the circle 

 myself. With the dark heather as a background, the floating 

 globules between us and it were able to send us sufficient light 

 to render the completion of the band visible. M. Cornu has 

 recently communicated to the Paris Academy of Sciences an 

 account of a white bow observed by himself. This leads me to 

 hope that the phenomenon observed at Hind Head may possess, 

 for scientific men, sufficient interest to justify some notice of 

 it in the Philosophical Magazine*. 



Looking since last month into the literature of the rainbow, 

 I find, thanks to Professor Dewar, that an interesting series 

 of experiments on showers derived from liquids other than 

 water has been executed by Dr. Hammerlf, who, however, 

 made use of solar instead of artificial light, and could, there- 

 fore, hardly ha se obtained the effects described by me. An 

 inspection of Sir John HerschePs Table of refractive indices 

 suggests, among others, spirit of turpentine, petroleum, and 

 a solution of chloride of ammonium as suitable liquids for rain- 

 bows ; and with these liquids both Dr. Hammerl and myself 

 have experimented — he first, and I afterwards. Dr. Hammerl's 

 paper leads me to express the hope that he may have the oppor- 

 tunity afforded him of continuing his investigations. 



I have also to refer to an interesting analysis of the 

 rainbow published by the Abbe Raillard as an Appendix to 

 his translation of my ' Notes on Lighj.' In the Comptes 

 Rendus, M. Raillard combated with great ability the notion 

 (which never took root in England) that fog was composed of 

 little bladders or vesicles, instead of full droplets; and in his 

 appendix he lays particular stress on that portion of Dr. 

 Young's theory which refers to the smallness of the drops. 

 He also mentions certain experiments executed by M. Salles- 

 Grirons, an account of which I have been unable to find. 

 M. Salles-Girons is described as the inventor of a " pulverizer 

 of liquids," which must be similar to those employed in the 

 Houses of Parliament. It is, as I have already said, a modi- 

 fication of an arrangement used by Savart. Rainbows were 

 produced from the spray thus obtained ; and the finer the 

 water-dust the less colour was shown by the rainbow. The 

 steam-boiler referred to in my last communication, as com- 



* The white rainbow was first observed by Ulloa on the mountain 

 Parnbamarca in Peru, and described in a work published under the 

 auspices of the King of Spain in 1748. The French translation consulted 

 by me was published in Amsterdam and Leipzig in 1752. 



t Sitzungsberichte der Wienei Akademie for July 1882. 



