106 Mr. T. Andrews. [June 5, 



But when the observations came to be finally reduced, it was found 

 that the difference between Colonel Herschel's results at Kew and 

 Greenwich, as shown independently by the three pendulums, had an 

 extreme range of about seven vibrations in the daily vibration 

 number. The cause of these differences was mysterious and inex- 

 plicable, and there was no alternative but to swing the pendulums a 

 second time at the two observatories. 



The revisionary work was undertaken by the observatory staff at 

 each place, in such intervals of leisure as they could obtain from their 

 regular operations. The final results, by the three pendulums, make 

 the vibration number at Kew in excess of that at Greenwich by 1'56, 

 1'50, and O59, giving an average excess of 1'22. 



The correction to this quantity for the excess of height of the 

 Greenwich over the Kew Observatory is O58. Thus, the revisionary 

 operations, reduced to the mean sea-level, make the excess of Kew 

 over Greenwich = 0'64 of a vibration, which may be accepted as 

 very fairly probable. 



II. " Observations on Pure Ice." Part II. By THOS. ANDREWS, 

 F.R.S., M.Inst.C.E. Received May I, 1890. 



The Plasticity of Ice. 



In a paper, ' Roy. Soc. Proc.,' vol. 40, 1886, p. 544, 1 recorded the 

 result of " Observations on Pure Ice and Snow," and having sub- 

 sequently had occasion to use large quantities of low temperature 

 freezing mixtures in the prosecution of other investigations, it seemed 

 desirable to take advantage of the opportunity, and to further utilise 

 the freezing mixtures in making collaterally the following additional 

 experiments bearing on some of the plastic or viscous properties of 

 ice at various temperatures. Messrs. J. C. McConnel and D. A. Kidd, 

 in their valuable and interesting paper on " The Plasticity of Glacier 

 and other Ice " (' Roy. Soc. Proc.,' vol. 44, 1888, p. 331), remark that 

 " the variation of the plasticity of ice with the temperature is of great 

 interest both for the theory of glaciers and for the explanation of the 

 plasticity itself." I hope, therefore, that the experiments now re- 

 corded may assist in affording some information in connexion with 

 this subject. An acquaintance with the causes of the flow of glaciers" 

 can scarcely be complete without some accurate experimental know- 

 ledge of the plasticity of ice at various temperatures, and it was 

 partly with this object that the following experiments were com- 

 menced. The experiments form a continuation of those contained in 

 my former paper. The arrangement of apparatus is described below, 

 and illustrated by the accompanying sketch, fig. 1. 



