I860.] Professor Tyndall^ on Alpine Phenomena, 26^ 



WEEKLY EVENING MEETING, 



Friday, June 1, 1860. 



Sib Roderick I. Murchison, D.C.L. F.R.S. Vice-President, 

 in the Chair. 



John Tyndall, Esq. F.R.S. 



PBOFE860B OF KATUBAL PHIIX360PHT, ROYAL INSTITUTION. 



Remarks on some Alpine Phenomena, 



The discourse consisted of an account of a winter's expedition to the 

 Alps, undertaken at the close of December 1859. The speaker 

 remained two nights at the Montanvert; and determined with a 

 theodolite the motion of the Mer-de-glace. This amounted to 

 about one- half of the summer motion, and exhibited the results, as 

 regards the quicker motion of the centre, established by measurements 

 made in summer. He described the crystals of the snow which fell 

 almost without intermission during the progress of the measurements. 

 He afterwards visited the vault of the Arveiron, and found a turbid 

 stream issuing from it, indicating that even in winter the motion of the 

 glacier along its bed, by which the rocks over which it passes are 

 ground, is not suspended even in winter. 



The gorgeous crimson of the western heaven, as observed from the 

 vault, gave occasion for some observations and experiments on the 

 colour of the sky. The hypotheses of Newton and Goethe were 

 referred to, as were also the memoirs of Clausius and Brucke. It was 

 explained that the blue of the firmament is due to reflected light, and 

 the morning and evening red to transmitted light. The possible action 

 of particles suspended in the atmosphere was illustrated. A solution 

 of mastic in alcohol recommended by Brucke was dropped into water, 

 and the resin precipitated : light reflected by the liquid containing 

 these particles appeared blue; while the transmitted light appeared 

 yellow, and on increasing the precipitate deepened to orange, and 

 became finally blood red. Professor Forbes has made the interesting 

 observation that steam, at a certain stage of its condensation, is blue 

 by reflected and red by transmitted, light. 



The colour of milk, of the juices of many plants, and of the colour 

 of a blue eye were also referred to as illustrative of the same action. 



[J. T.] 



