Ebel Chamouni 14 feet Ebel Grindelwald 25 " Hugi Aar 240 " Agassiz Aar 200 " Bakewell Mer de Glace 540 " De la Beche Mer de Glace 600 " Shirwell Mer de Glace 300 " M. Rendu Mer de Glace 365 " Saussure's Ladder Mer de Glace 375 " ... Such was the state of our knowledge when Professor Forbes undertook the investigation of the subject." I am persuaded that the writer of this article will be the first to applaud any attempt to remove an error which, advanced on his great authority, must necessarily be widely disseminated. The numbers in the above table certainly differ widely, and it is perhaps natural to conclude that such discordant results can be of no value; but the fact really is that _every one of them may be perfectly correct_. This fact, though overlooked by Professor Forbes, was clearly seen by Rendu, who pointed out with perfect distinctness the sources from which the discrepancies were derived. [Sidenote: DISCREPANCIES EXPLAINED.] "It is easy," he says, "to comprehend that it is impossible to obtain a general measure,--that there ought to be one for each particular glacier. The nature of the slope, the number of changes to which it is subjected, the depth of the ice, the width of the couloir, the form of its sides, and a thousand other circumstances, must produce variations in the velocity of the glacier, and these circumstances cannot be everywhere absolutely the same. Much more, it is not easy to obtain this velocity for a single glacier, and for this reason. In those portions where the inclination is steep, the layer of ice is thin, and its velocity is great; in those where the slope is almost nothing, the glacier swells and accumulates; the mass in motion being double, triple, &c., the motion is only the half, the third, &c. [Sidenote: LIQUID MOTION ASCRIBED TO GLACIER.] "But this is not all," adds M. Rendu: "_Between the Mer de Glace and a river, there is a resemblance so complete that it is impossible to find in the latter a circumstance which does not exist in the former._ In currents of water the motion is not uniform, neither throughout their width nor throughout their depth; _the friction of the bottom, that of the sides_, the action of obstacles, cause the motion to vary, _and only towards the middle of the surface is this entire...._"[J]