ON THE MOVEMENT OF SCREE-MATERIAL. 825 



47. Second Note on the Movement of Scree-Matertal. By 

 Charles Davison, M.A., Mathematical Master at King Edward's 

 High School, Birmingham. (Read June 6, 1888.) 



(Communicated by Prof. T. G. Bonney, D.Sc, F.E.S., F.G.S.) 



[Abridged.] 



The first results of the experiment described in this note, namelj^ 

 those relating to the period from May 5 to September 22, 1887, 

 have already been recorded in a paper read before the Geological 

 Society on February 29, 1888 *. 



After a brief interval the experiment was continued under the 

 same conditions as before, from October 4, 1887, to May 5, 1888, 

 with the object of comparing the rates of descent in the winter and 

 summer halves of the year, and also of determining the effects on 

 creeping of rain and snow. 



Allowing a distance of | mm. for the interval of 12 days during 

 which the experiment was suspended, the total descent during the 

 year was 13^- mm. (^. e. a little more than half an inch), the mean 

 rate of descent being therefore "00140 inch per day. 



Comjycmson of the Rates of Descent during the Winter and Summer 

 Months. — Dividing the year of the experiment into winter, from 

 October 4, 1887, to April 3. 1888, and summer, from May 5 to 

 October 4, 1887, and April 3 to May 5, 1888, we have : — 





Average daily 



Total descent 



Eate of descent 





range of tem- 



in mm. 



in inches per 





perature t. 





day. 



Summer (184 days),.. 



... 14°-4F. 



8 



•00171. 



Winter (182 days)... 



... 8°-0 



5^ 



•00112. 



Had the creeping movement been proportional to the range of 

 temperature, the average daily descent during the winter, compared 

 with that during the summer, would have been rather less, namely 

 •00095 inch per day. Not only, however, is the heat of the sun 

 more intense in summer than in winter, and consequently the effects 

 produced by passing clouds so much the greater, but also for about 

 three months of winter the experimental stone was entirely shielded 

 from the sun by surrounding houses. Clearly, then, other causes 

 must have operated in producing the comparatively rapid rate of 

 descent during the wiuter months. 



Lifluence of Snow. — The heavy snow-storms which visited many 

 parts of England during the last winter were represented at 

 Birmingham by very meagre falls. Except between February 14 

 and March 28, the snow seldom lay upon the ground, and when, on 

 several occasions between these dates, it did lie for a short time, the 



* Quart. Journ. Geol. Soc. for May 1888, p. 232. 



t Excluding 20 days from August 6-25, and 8 days from February 15-22. 



