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XIV. On the Physical Phenomena of Glaciers.— I. Observations on the Mer de Glace. 
By John Tyndall, F.B.S., Membre de la Sodete Hollandaise des Sciences ; la SodHe 
de Physique et d'Eistoire Naturelle de Geneve ; la Sodde Philomathique de Paris ; 
Mitglied der Eaturfcrrschenden Gesellschaft, Zurich, der Gesellschaft zur Beforderung 
der Gesammt-Naturwissenschaften, Marburg, der K. Leap. Akad. der Naturforscher, 
Breslau, and Professor of Natural Philosophy at the Boyal Institution. 
Eeceived May 20, — Eead May 20, 1858. 
§ 1 . 
The Philosophical Transactions for 1857 contain a paper by Mr. Huxley and myself 
upon the Structure and Motion of Glaciers. The observations on which that paper was 
founded extended over a very brief period, and hence arose the desire, on my part, to 
make a second expedition to the Alps, in which I regret to say my friend was unable 
fully to join. Ihe phenomena of the Mer de Glace being those on which the most 
important theoretic views of the constitution and motion of glaciers are based, I wished 
especially to make myself acquainted by personal observation with these phenomena. 
Six weeks of the summer of 1857 were accordingly devoted to the examination of this 
glacier. For the purpose of observing its motion, bearings and inclinations, and also of 
determining its width at various points, I took with me an excellent 5-inch theodolite, 
and a surveyor’s chain ; for both of which I am indebted to the kindness of the Director- 
General of the Geological Survey, and to Professor Pamsay. I propose to divide the 
investigation into two parts, the first of which forms the subject of the following paper, 
while the second will be the subject of a future communication. It gives me great 
pleasure here to record my grateful sense of the able and unremitting assistance rendered 
me throughout the entire period of the observations, by my friend Mr. T. A. Hirst, 
whose name indeed, had he permitted it, I should gladly have seen associated with my 
own at the head of this paper. 
§ 2. On the Motion of the Mer de Glace. 
Our first observation of the motion of the Mer de Glace was made on the 14th of 
July. On the steep terminal incline of the Glacier de Bois we singled out a tall pinnacle 
of ice, the front edge of which was perfectly vertical. In coincidence with this edge I 
fixed the vertical wire of our theodolite, and after three hours found that the ice cliff 
had moved downwards, the cross hairs being now projected against the face of the cliff 
several inches above its edge. 
Our first line across the glacier was set out upon the 17th of July. The mode of 
proceeding in all such cases was this : — the theodolite was placed beside the glacier, quite 
mdcccliz. 2 N 
