20 ROYAL SOCIETY OF CANADA 



Electrical Properties of Ice. 



Insulating Properties. — Ice appears to be a good insulator. Thus 

 telephone cables, which are defective through moisture, become per- 

 fectly right when the air temperature falls below freezing. S. P. Bou- 

 vier, in 1803, showed that ice could not be used to replace water in the 

 dry pile. Dellmann, however, in 1864, investigated the insulating pro- 

 perties of ice and found them the same as water even down to 8 or 10 

 degrees below freezing, which does not seem to accord with practical 

 experience. 



Dielectric constant. — The dielectric constant of ice at — 24:° Cent, 

 has been found to lie between 60 and 78, values not far from pure water. 



F. Beaulard, in 1905, made a determination of the dielectric con- 

 stant of water, which he extended to ice in 1907. His method was to 

 contain the substance in an ellipsoid glass vessel, suspended in a high 

 frequency alternating electrostatic field. The axes of the ellipsoid were 

 all inclined to the field. The couple acting on it was determined when 

 the vessel was empty and then when it contained the substance. The 

 result obtained is given at 11.04, the low value of which as compared to 

 the generally accepted value 80, the author puts down to polarisation 

 effects in the usual methods of measuring dielectric constants. 



A still lower value is given as a result of later work, i.e., 3.072 for 

 water just at the freezing point. For ice just melting he gives 1.455. 

 The very low value for water was explained by the solubility of the glass. 

 It would seem that further study of this method is necessary before these 

 values can be accepted. 



Crystalline Structure. 



Snow crystals are the usual form met with and these assume many 

 beautiful shapes, usually six -rayed stellate forms of great variety and 

 delicacy. Hail appears often in hexagonal crystals, probably projected 

 from a solid nucleus. 



Wilson A. Bentley, of Jerico, Vermont, has made a most complete 

 study of snow crystals. He has shown and photographed as many as 

 200 different varieties, all of which have been described very elaborately 

 in the Monthly "Weather Eeview. 



He finds in fact that " Snow-crystals are divided into two great 

 classes, — those columnar in form and those of a tabular form. These 

 two fundamental types are in turn divided into many sub-varieties. 



" The forms vary according to the wind, the height of the clouds, 

 the degree of cold, the amount of water in the air, etc. Crystals formed 

 in cold weather or in high clouds are usually columnar or solid tabular. 



