On the Viscosity of Ice. 



491 



a Treatise on the Action of Nerve-centres and Modes of Growth. 



8vo. London 1887. The Author. 



Wernicke (Dr. A.) Die Grundlage der Euklidischen Geometrie 



des Maases. 4to. Braunschweig 1887. The Author. 



Wolf (Dr. R.) Astronomische Mittheilungen. No. 68. 8vo. 



Zurich 1887. The Author. 



" Note on some Experiments on the Viscosity of Ice." By 

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

 Unwin, F.R.S. Received April 13 —Read May 5, 1887. 



Owing to the uncertainty prevailing as to the continuous exten- 

 sibility of ice under tensional stress, it appeared to me desirable to 

 institute a series of experiments directed to this point, conducted 

 according to the methods, and, as far as possible, with the exactness 

 of modern experimental testing. 



In order to eliminate the influence of regelation, the experiments 

 have been carried on at such low temperatures as preclude the possi- 

 bility of any effect being produced by this cause, the highest tem- 

 perature recorded in Experiment No. 1 being — 2*6° C. ; in No. 2, 

 — 1*0° C. ; and in No. 3, —0*5° 0. It must be remarked, moreover, 

 that these maximum temperatures only obtained for a very short 

 time, on one or two days, as will be seen from the records. 



The testing machine which I used was constructed for me by 

 Herr Ingenieur Usteri-Reinacher, of Zurich. It was on the com- 

 pound lever principle, the ratio of the arms of the equivalent simple 

 lever being 1 : 20. All parts where friction could be prejudicial were 

 provided with knife-edges. The design of the machine is obvious 

 from the figure, in which A represents the specimen of ice to be 

 tested, held by the collars at B and C. D is an equipoise, to balance 

 the weights of the levers and of the vessel E, through which the 

 power is applied by means of shot. F is a hand- wheel fixed to the 

 screw G, by means of which, as the specimen extends, the under 

 collar C may be lowered, so that the position of the upper collar B 

 and of the two levers may remain the same. An index at H shows 

 when the parts of the instrument are in the relative position required, 

 and by its motion enables a rough estimate to be formed of the 

 extension of the specimen. 



The temperature was rendered more equable by enclosing the appa- 

 ratus in two wooden boxes, KL and MN. 



A delicate thermometer, graduated to tenths of a degree centigrade, 

 and reading from — 6° C. to + 6° C, was attached to the central 



