Polytechnic Association 007 



March 29, 1872. 



Prof. S. D. Tillman in the chair ; Robert Weir, Esq., Secretary. 

 The President read the following items of scientific news : 



I. The Flow of Glaciers. 



Prof. Tyndall, in a recent lecture on the movement of glaciers, after 

 describing the observations and measurements made by himself on the 

 Mer de Glace, gives the following clear statement touching the rela- 

 tive motion of different parts of a crooked river of ice: "When a 

 glacier moves through a sinuous valley, the locus of the point of maxi- 

 mum motion does not coincide with the center of the glacier, but, on 

 the contrary, always lies on the convex side of the central line. The 

 locus is, therefore, a curved line, more deeply sinuous than the valley 

 itself, and therefore crosses the axis of the glacier at each point of the 

 contrary flexure. This law holds good for water, substituting the 

 word river for glacier. The idea, then, as to the similarity between 

 a river and a glacier, becomes marvelously strengthened. The glacier 

 is like a river, because the central part moves faster than the sides ; 

 it is like a river, because its top moves faster than its bottom ; and, 

 again, it is like a river, because the point of swiftest motion follows 

 the sinuosities of its sides. 



Dr. J. W. Richards said that these facts proved that the ice was 

 not a solid body, but that there must be a softening and change of 

 position of the different parts. It was now supposed that there was 

 no such thing as an absolute solid. 



II. Ball Lightning. 

 Mr. C. F. Yarley has recently given to the Royal Society of Lon- 

 don an account of new experiments made with a Holtz electric 

 machine, having brass balls at the poles, about an inch in diameter. 

 A strip of wood about three inches in length was bent around the 

 negative pole, so as to project on each side of it toward the positive 

 pole. On rotating the machine, two bright spots are seen on the 

 positive pole. If the positive pole be made to rotate on its axis at 

 the same^ime, the luminous spots do not rotate with it ; but when 

 the negative pole with its filament of wood is rotated, the spots on 

 the positive pole rotate also. On interposing a non-conductor, like 

 plate-glass, between the poles, the luminous spots disappear. On 

 removing the wood from the negative pole, there was sometimes a 



