168 THE AMERICAN NATURALIST. [VOL XXXII. 
Meanwhile his observations had been already so complete 
that he felt himself justified in writing an extended work set- 
ting forth his glacial theories. This volume, entitled Eudes 
sur les Glaciers, was published in September, 1840, and was 
accompanied with eighteen beautiful plates. In the treatise 
explicit reference is made to the prior discoveries of Venetz 
and Charpentier, the work, indeed, being dedicated to them. 
Nevertheless, considerable ill feeling arose on account of this 
priority of publication. i 
In August, 1840, Agassiz returned to Hugi’s cabin on the 
Glacier of the Aar with the intention of occupying it, but found 
that it had disappeared, there being only some of the débris 
remaining two hundred feet below the position occupied by it 
the year before. Whereupon Agassiz proceeded to build for 
himself a shelter under the projecting side of a huge boulder 
which was a prominent object upon a medial moraine. With 
this as the centre, he, with numerous colaborers, carried on for 
three successive summers those minute and careful observa- 
tions upon glaciers which have been the basis of all subsequent 
speculation. In order to study the interior construction, they 
made deep borings into the ice, and on one occasion Agassiz 
was let down by a rope one hundred and twenty feet into a 
crevasse, while on another he spent a lonely night on the 
Siedehlhorn. To determine the rate of motion, he set a row 
of stakes across the glacier and took observations to determine 
their changes of position during an extended period. 
While this work was in progress, Agassiz was visited by 
James D. Forbes, an English engineer of eminence, who spent 
some weeks with the party on the Aar Glacier in 1841. A 
year later Forbes returned to Switzerland and with his accu- 
rate mathematical instruments made observations upon the 
Mer de Glace sufficient to determine accurately the laws of its 
motion. A report of this was published by Forbes in the 
Edinburgh Mew Philosophical Journal in its issue for October, 
1842. The report was dated, however, July 4, 1842. Mean- 
while Agassiz had published the results of his observations 
upon the movements of the Aar Glacier in the Comptes Rendus 
of the 29th of August, 1842, two months before the publica- 
