276 Til K Lin: OF JAMES I). FORBES. [CHAP. 



latter presented a solid wall of ro<jjt in contact with the 

 ice, and upon this, as upon a fixed wall or dial, might be 

 marked the progress of the glacier as it slipped by. 



' The instrument destined for all these observations 

 was a small astronomical circle, or 4^-inch theodolite, 

 supported on a portable tripod. A point of the ice 

 whose motion was to be observed, was fixed by a hole 

 pierced by means of a common blasting iron or jumper 

 to the depth of about two feet. An accurate vertical 

 hole being made, the theodolite was nicely centered on 

 it by means of a plumbline, and levelled. A level run 

 directly to the vertical face of the rock, gave at once 

 the co-ordinate for the vertical direction, or height of 

 the surface of the glacier. The next element was the 

 position or co-ordinate parallel to the length, or direc- 

 tion of motion, of the glacier. This was obtained by 

 directing the telescope on a distant object, nearly in 

 the direction of the declivity of the glacier, which 

 object was the S.E. angle of the house at the Mont- 

 jmvert, distant 5,000 feet. The telescope was then 

 moved in azimuth exactly 100 to the left, and thus 

 pointed against the rocky wall of the glacier, which 

 was here very smooth and nearly perpendicular. My 

 assistant, Balm at, was stationed there with a piece of 

 white paper, held with its edge vertical, which I directed 

 him by signs to move along the surface of the rock, until 

 it coincided with the vertical wire of the telescope. Its 

 position was then marked on the stone with a chisel, and 

 the mark painted red with oil paint, and the date affixed. 

 These marks, it is believed, will remain for years. . . . 



' It was with no small curiosity that I returned to the 

 station of the " Angle " on the 27th, the day following 

 the first observation. The instrument being pointed 

 and adjusted as described, and stationed above the hole 

 pierced in the ice the day before, when the telescope 

 was turned upon the rock, the red mark was left far 

 above ; the new position of the glacier being 16 '5 inches 

 lov^er that is, more in advance than it had been twenty- 

 six hours previously ! Though the result could not be 



