Report of the Researches of M. Agassiz. 159 



mination of the annual advance in the different portions of 

 the glacier. It was not less urgently required for theory, that 

 we should have a knowledge of the exact manner of the daily 

 movement, and especially of the difference between the diur- 

 nal and nocturnal movement of the entire mass. With this 

 object in view, M. Agassiz caused a stake to be fixed in the 

 ice, at the distance of about 500 feet from the margin of the 

 left bank of the glacier. A telescope was fixed on a rock, and 

 every morning an observation was made as to the distance 

 the stake had moved from the vertical thread of the telescope. 

 These observations, made quite regularly for nearly a month, 

 from the 3d to the 26th of August, every morning and even- 

 ing at seven o'clock, have given the mean advance at 3 J inches 

 in the 24 hours. The proportion of the diurnal movement to 

 the nocturnal has been as six to seven. This excess in fa- 

 vour of the night, however minute it may be, must be deter- 

 mined more accurately, as Professor Forbes has obtained a result 

 completely opposite, at the Glacier des Bois. M. Agassiz ex- 

 plains this difference, by referring it to the difference in the 

 hours at which the observations were made. He conceives 

 that Professor Forbes, by including the hour from six to seven 

 in the morning in the series of diurnal hours, has given to 

 that series an hour which belongs to the nocturnal one, and 

 that an hour in which the movement is probably most of all 

 considerable. In fact, as soon as you commence to compare 

 the diurnal temperature with the nocturnal, it is necessary 

 that you place the commencement of the glacier day at the 

 time that the melting of the ice begins to be seen, and the 

 watery rivulets commence to run. Now, this period never 

 commences before seven in the morning, even in the hottest 

 days. 



Regarding the extent of the movement (3^ inches), it may 

 probably be considered very small, when compared to the sum- 

 total of the annual movement. But here it ought to be re- 

 membered, that the stake in question indicates the advance 

 of a portion of the glacier which is very near its margin ; now, 

 it is probable that, judging from the relative movements of 

 the margin and the centre mentioned above, if the stake, 

 instead of having been placed at the distance of 500 feet from 



