MOTION OF GLACIERS DES BOIS AND BOSSONS. 
1S7 
Table VI. 
Mean Temperatures (by periods) on the Centigrade Scale, observed at Geneva and 
the Great St. Bernard*. 
Geneva. 
St. Bernard. 
Means of Max. and Min. 
Max. 
Min. 
Max. 
Min. 
Geneva. 
St. Bernard. 
1844. Oct. 2 to Oct. 14. . . 
17-37 
8-57 
4-16 
— 1-58 
12-97 
1-29 
Oct. 14 to Nov. 2. . . 
11-77 
5-13 
1-61 
- 4-93 
8-45 
- 1-66 
Nov. 2 to Nov. 19. . . 
11-84 
3-11 
1-62 
- 5-66 
7-47 
— 2-02 
Nov. 19 to Dec. 4. . . 
4-93 
- 0-18 
— 5-11 
— 11-25 
2-27 
- 8-18 
Dec. 4 to Jan. 7«- • • . 
1-45 
- 2-40 
- 5-70 
-10-96 
- 0-27 
- 8-33 
1845. Jan. 7 to Feb. 18. .. 
1-47 
— 4-11 
- 6-92 
-13-86 
— 1-32 
-10-39 
Feb. 18 to March 18. 
4-76 
- 2-74 
- 3-93 
— 12-56 
1-01 
— 8-24 
March 18 to April 17- 
11-27 
1-57 
0-19 
— 10-13 
6-42 
- 4-97 
April 17 to May 17. 
16-04 
5-56 
5-15 
- 6-36 
10-80 
- 0-60 
May 17 to May 31.. . 
16-83 
6-91 
6-04 
— 4-67 
11-87 
0-68 
May 31 to June 19-. . 
23-70 
12-71 
11-48 
Ml 
18-20 
6-29 
June 19 to July 4. . . 
22-58 
12-13 
9-81 
0-53 
17-35 
5-17 
July 4 to July 18. . . 
24-01 
12-84 
10-20 
2-08 
18-42 
6-14 
July 18 to Aug. 6. . . 
23-28 
13-20 
9-25 
1-68 
18-24 
5-46 
Aug. 6 to Oct. 8 
21-15 
11-31 
7-57 
0-10 
16-23 
3-83 
Oct. 8 to Nov. 8 
11-84 
3-78 
2-38 
— 3-70 
7-81 
— 0-60 
Nov. 8 to Nov. 21 . . . 
12-54 
5-86 
— 1-03 
- 6-06 
9-20 
- 3-54 
A general comparison of the curves of temperature and those of glacier motion 
(more particularly on the Glacier des Bois) affords a proof of the justness of the prin- 
ciple laid down by me in 1842, that the motion of the ice “is more rapid in summer 
than in winter, in hot than in cold weather, and especially more rapid after rain, and 
less rapid in sudden frosts-^;” the evidence of the connection is plainer by mere 
inspection than any detail could make it. But I request attention to the apparent 
anomalies of the curves, as affording a stronger evidence of the fidelity with which 
the measurements have been made, and to the truth of the plastic theory, than per- 
haps even the general coincidence just referred to. 
If the velocity of the glacier depend upon the completeness of its infiltration with 
water, rendering the whole an imbibed porous mass like a sponge, it cannot depend 
solely on the mean temperature of any period, but also upon the wetness of the 
surface, whether derived from mild rain, from thawing snow, or from any other me- 
teorological accident which the register of the thermometer cannot of itself indicate*. 
Further, a thick coating of snow on the glacier must defend it from the excessive 
cold of winter just as it defends the earth and plants, and consequently the minimum 
of motion will not necessarily coincide with the minimum of temperature. Now to 
* The last three lines have been added during printing. 
t Fourth Letter on Glaciers, Edinburgh Philosophical Journal, Jan. 1843 ; and Appendix to Travels, 2nd 
edit. p. 415. 
+ “ The proportion of velocity does not follow the proportion of heat, because any cause, such as the melting 
of a coating of snow by a sudden thaw, as in the end of September 1842, produces the same effect as a great 
heat would do.” — Travels, 2nd edit., p. 372. 
