264 LOUIS AGASSIZ. [CHAP. xi. 



direction and supervision. Chapter by chapter, Agassiz 

 looked over the manuscript, correcting with pencil, and 

 indicating additions to be made. The manuscript was 

 finished before Agassiz left Paris, and went to the 

 printer between November, 1846, and April, 1847; first 

 under the direction of Desor, who left Paris at the end 

 of February, 1847, an d afterward under the direction 

 of Charles Martins, who wrote the introduction and fin- 

 ished the excellent list of works on the present glaciers. 

 Thus the volume is a rather composite one, through the 

 collaboration of Desor and Martins, and as a whole, is 

 less important than Agassiz's first volume on the gla- 

 ciers, although it contains many new facts. The truth 

 is, that Agassiz and Desor were not physicists ; and 

 although Martins and Bravais, who were good physi- 

 cists, helped them with their advice at the glacier of 

 the Aar, they failed to recognize the plasticity of gla- 

 ciers, as Bishop Rendu and James Forbes had done 

 in the case of the Savoy glaciers ; and it was reserved 

 for the great English physicist, John Tyndall, to solve 

 the problem of the conversion of snow into ice by pres- 

 sure, to find the cause of glacier motion in pressure, 

 regelation, crystallization, and internal liquefaction, - - a 

 splendid discovery which was made between 1856 and 

 1859, and published in 1860, in a work entitled " Gla- 

 ciers of the Alps." 



Beside the publication of the volume on the glaciers, 

 Agassiz, during his stay in Paris, greatly advanced the 

 acceptance of the glacial doctrine by all unprejudiced 

 geologists. In a communication made before the Geo- 

 logical Society of France, at the meeting of the 6th of 



