1887.] Dr. J. F. Main. On the Viscosity of Ice. 



329 



noted in the flakes of mica or any other mineral of somewhat like 

 form scattered through the mass of the rock, sometimes approximating 

 to a banding of the constituents, without any indication of this being 

 the result of crushing. In regard to this particular structure, it is 

 worth notice that it often lies in planes making a low angle with the 

 horizon. 



(3.) The same result may help to explain the assertion so frequently 

 made, that among the older rocks the foliation (or minor mineral 

 banding) is commonly parallel to the (apparent) stratification (or 

 major mineral banding) . This also I have noticed in cases where 

 either there was no indication of subsequent crushing, or the latter 

 had not effaced, and its effects could be distinguished from, the earlier 

 structure of the rock. I once supposed this parallelism and te .dency 

 to horizontality to be due to the weight of superimposed beds, but for 

 some time have been dissatisfied with this explanation, because I could 

 find no evidence that any heavy burden had been laid upon the older 

 rocks till long after they had assumed a foliated structure. Tension, 

 however, would probably produce the structure at least as readily as 

 pressure, and the former of course would, as a rule, act parallel with 

 the surface of the earth's crust, while compression should be exhibited 

 commonly in planes making a high angle with it. 



V. " Note on some Experiments on the Viscosity of Ice. 5 ' By 

 J. F. Main, M.A., D.Sc. Communicated by Prof. W. C. 

 Unwin, F.R.S. Received April 13, J 887. 



(Abstract.) 



The paper contains an account of some experiments on the con- 

 tinuous extension of bars of ice subjected to tension, made during 

 the last winter in the Engadine. To eliminate the influence of rege- 

 lation, the experiments have been carried on at such low temperatures 

 as preclude the possibility of any effect being produced hy this cause. 

 The highest temperatures during the experiments were — 2'6° G. in 

 Experiment I; — 1'0° C. in Experiment II ; and — 0'5 o C. in Expe- 

 riment III. These maximum temperatures only obtained for a very 

 short time on one or two days. 



The bar3 were tested in a compound lever testing machine with 

 accurate knife edges, the load being a known weight of shot. The 

 whole apparatus was enclosed in a double wood box. A delicate 

 thei mo meter graduated to tenths of degrees, attached inside the box, 

 "gave the temperature at any given time, and the range of variation 

 of temperature was recorded by two maximum and minimum ther- 

 mometers, fi\ed inside to the roof of the inner box. To obtain ice 



