﻿Intelligence and Miscellaneous Articles. 235 



its descent, except at its end, must press against its end, by reason 

 of its weight, with a force of 194*42 lbs. But the cubical inch of 

 solid ice at its extremity opposes, by the shear of its three surfaces 

 whose attachment to the adjacent ice is unbroken, a resistance of 

 3 X 75 lbs., or 225 lbs. That resistance stops therefore the descent 

 of this strip of ice, one mile long, having no other resistance than 

 this opposed to its descent, by reason of its detachment from the 

 rest*. It is clear, then, that it could not have descended by its 

 weight only when it adhered to the rest, and when its descent was 

 opposed by the shear of its whole length ; and the same may be 

 proved of any number of miles of strip in 'prolongation of this. 

 Also, with obvious modifications, it may be shown, in the same way, 

 to be true of any other similar strip of ice in the glacier, whether 

 on the surface or not, and therefore of the whole glacier. 



It results from this investigation that the weight of a glacier is 

 insufficient to account for its descent ; that it is necessary to con- 

 ceive, in addition to its weight, the operation of some other and 

 much greater force, which must also be such as would produce 

 those internal molecular displacements and those strains which are 

 observed actually to take place in glacier ice, and must therefore be 

 present to every part of the glacier as its weight is, but more than 

 thirty-four times as great. 



XXXII. Intelligence and Miscellaneous Articles. 



FORMATION OF AN ARTIFICIAL SPECTRUM WITH ONE 

 FRAUNHOFER's LINE. BY A. WULLNER. 



ACCORDING to KirchhofFs explanation of Fraunhofer's lines, 

 they are formed by an absorption in the ignited gas sur- 

 rounding the solid core of light of particular wave-lengtbs emitted 

 from the core. If the solar atmosphere alone sent us light, these 

 lines, assuming that the intensity of the light proceeding from the 

 atmosphere was great enough, must appear bright upon a dark 

 ground. This inversion may possibly be observed at the total 

 eclipse of next August. 



I may be allowed to communicate an experiment which shows the 

 phenomenon with a terrestrial source of light, in the same manner as 

 Kirchhoff has concluded for the sun from the absorption of light in 

 flames. 



If the discharges of a Leyden jar of about a square foot of coated 

 surface, and a small striking-distance, be passed through a Geissler's 

 spectrum-tube of the usual form by the aid of a Holtz's machine, the 

 tube being held before the slit of a spectrometer, the spectrum of 

 the gas enclosed in the tube is first seen as on the passage of a pow- 

 erful induction-current. If the striking-distance be only a little in- 



* If, however, the glacier were inclined at 35° 10', instead of 4° 52', and a 

 strip were detached from its surface, as described above, it would equal the shear 

 of one cubic inch at its lower end, if it were 300 yards long, and if the glacier 

 were vertical, when it was 172-8 yards long. 



