Observations on Glaciers. 348 



nothing at tbe upper extremity of the glacier, to a maximum 

 at its lower end. The former experiment had, I have since 

 learned, been suggested by Professor Studer to M. Escher last 

 year, and attempted to be put in practice (though unsuccess- 

 fully) by the latter, on the glacier of Aletsch. Admitting 

 Charpentier's theory, however, this dilatation would be too 

 small to be successfully observed in a moderate time, and with 

 the geometrical methods which the uneven and varying surface 

 of the glacier enables us to employ ; I have therefore not at- 

 tempted it. The other method, in fact, embraces both ends ; 

 for if the movement of the glacier in its upper and lower part 

 be determined (by upper I mean near its origin), the differ- 

 ence of the motions determines the dilatation or contraction 

 of the intermediate part of the ice, and is liable to none of 

 the great errors arising from the measurement of long distances. 

 The observation, in the simplest and best form which I em- 

 ploy, resembles perfectly that of determining with the transit 

 instrument the progress of a planet. 



I have already said that my later observations confirm those 

 which I previously communicated ; any variations, indeed, 

 arise solely from a change of circumstances or season, and not 

 from errors of observation. (1.) The continuous impercep- 

 tible motion of the glacier is entirely confirmed ; its bearing 

 upon the sliding theory is very obvious. (2.) This motion is 

 not by any means the same, however, from day to day and 

 from week to week, as indeed already appeared from my first 

 results. (8.) This variation of motion appears to be common 

 to every part of the glacier, as well where compact and com- 

 pletely even, as where most fissured ; nor perhaps is the va- 

 riation of velocity greater in one case than in the other. 

 (4.) From numerous observations, made in all parts of the gla- 

 cier, it invariably results as before, that the centre moves 

 faster than the sides of the ice-stream. In the lower and 

 faster moving part of the glacier this disproportion is great- 

 est, varying from one-third to one-half of the smaller velo- 

 city. Near the origin of the glacier it appears to be one- 

 fourth or one-fifth of the smaller velocity. (5.) The variations 

 of glacier motion aff'ect the central parts most sensibly, 

 (6.) The greatest daily motion which 1 have observed, nearly 



