26th, Oct, 1856.
My dear Sir
During my recent visit to the Continent my attention was perpetually attracted to the beautiful colour of the water in many rivers. Down the Stelvio pass,2 for example, on the Italian side there is a stream which shines sometimes like a fluorescent solution of sulphate of quinine.3 I am told that the colour of the Rhone as it leaves the lake of Geneva (which unhappily I have not yet seen) is a deep and beautiful blue.4 Would you kindly inform me whether any experiments have been made with a view of determining the true cause of this colour?5 I do not think it can be referred to the natural colour of the water, as I am sure a layer of distilled water of equal depth would not produce some of the effects that I have seen in the rivers of the Tyrol.
During my holiday I spent many days upon the glaciers with my friend Mr Huxley. We paid much attention to the structure of the ice, a theory of which has been propounded by Prof Forbes. I cannot agree with this theory,6 and when I have time to put my observations together I will tell you more particularly the grounds of my dissent.
Believe me dear Sir | Most sincerely Yours | John Tyndall
RI MS JT/1/339
LT Transcript Only
The letter lacks an addressee, but was clearly addressed to de la Rive from the answer he made from Venice on 7 November 1856, for which see volume 6.
Stelvio pass: The highest mountain pass in northern Italy and in the southern Tyrol at an elevation of 9,045 ft. Tyndall and Frankland had been through the pass between 3 and 4 September 1856 (RI MS JT/13c/898).
sulphate of quinine: Quinine, an alkaloid prepared from the bark of the cinchona tree, had been used to treat malaria since the seventeenth century. It was commercially purified and sold as quinine sulphate whose fluorescent properties were first noted by John Herschel in 1845.
A deep and beautiful blue: Tyndall saw this for himself in July 1857 and attributed it to the refraction of light by suspended particles derived from rocks ground down by glaciers. He made no reference to any observers who had previously tried to explain the phenomenon despite having been supplied these by de la Rive. See J. Tyndall, Glaciers of the Alps (London: J. Murray, 1860), pp. 33–4, 261–2, and RI MS JT/2/13c/952–4. For de la Rive’s reply on 7 November 1856, see vol. 6.
the true cause of this colour: See note 3. Although probably not suggesting the blue colour was due to fluorescence, it can be caused by organic matter in the waters.
I cannot agree with this theory: Forbes’s viscous theory of glacial structure and motion. See letter 1274, n.13 and Introduction to this volume.
Please cite as “Tyndall1289,” in Ɛpsilon: The John Tyndall Collection accessed on