CENTRE MOVES QUICKEST.

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tion ; quite contrary to the opinion generally entertained.”He also announced at the same time the continuoushourly advance of the glacier. This letter bears the date,“ Courmayeur , Piedmont, 4th July,” but it was not pub-lished until the month of October following.

Meanwhile M. Agassiz, in company with M. Wild, re-turned to complete his experiment upon the glacier of theAar. On the 20th of July, 1842, the displacements of thesix piles which he had planted the year before 'were de-termined by means of a theodolite. Of the three uponthe Finsteraar affluent, that nearest the side had moved160 feet, the next 225 feet, while that nearest to the centrehad moved 269 feet. Of those on the Lauteraar, thatnearest the side had moved 125 feet, the next 210 feet,and that nearest the centre 246 feet. These observationswere perfectly conclusive as to the quicker motion of thecentre: they embrace a year’s motion; and the magnitudeof the displacements, causing errors of inches, which mightseriously affect small displacements, to vanish, justifies usin ranking this experiment with the most satisfactory ofthe kind that have ever been made. The results werecommunicated to Arago in a letter dated from the glacierof the Aar, on the 1st of August, 1842 ; they were laidbefore the Academy of Sciences on the 29th of August,1842, and are published in the ‘ Oomptes Rendus’ ofthe same date.

The facts, then, so far as I have been able to collectthem, are as follows:—M. Agassiz commenced his ex-periment about ten months before Professor Forbes, andthe results of his measurements, with quantities stated,were communicated to the French Academy about twomonths prior to the publication of the letter of ProfessorForbes in the ‘Edinburgh Philosophical Journal.’ Butthe latter communication, announcing in general termsthe fact of the speedier central motion, was dated from

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