Geological Society. 315 



way that the sign of the return charge after discharge and insula- 

 tion should chauge once or more. 



3. This anticipation was verified by charging the flask alternately 

 positively and negatively for successively decreasing periods. The 

 author learned after making this verification that Sir William 

 Thomson had tried similar experiments before, but had never 

 formally published them. 



4. The analogy between coercive force in magnetism and the 

 electro-coercive force suggested that, as mechanical agitation shakes 

 out the magnetism from a magnet, so it might shake down the 

 electropolar state of a dielectric and unmask residual charge more 

 rapidly than is the case in quiescence. This was found to be the 

 case ; a residual charge manifests itself in the flask more rapidly 

 when the flask is tapped than when it is quiet. It was also found 

 that that portion of the return charge which comes out last is more 

 accelerated by vibration than that which comes out first, and that, 

 after tapping, the flask was less susceptible to the effect of tapping 

 than it was before it was touched. 



. 5. Experiment shows that, after a return charge has attained a 

 maximum and is decreasing by conduction through the glass, the 

 loss per cent, per unit of time does not continuously increase from 

 zero at the point of maximum potential but may presently decrease. 

 6. Sir William Thomson explained specific inductive capacity by 

 supposing every part of the dielectric to be electropolar under in- 

 duction ; by introducing time into that explanation, it is made to 

 cover both specific inductive capacity and that on which residual 

 charge depends as respectively rapid and slow cases of similar phe- 

 nomena. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 153.] 



June 21st, 1876.— Prof. P. Martin Duncan, ALB., F.K.S., President. 

 in the Chair. 



The following communications were read : — 



1. " On the Ice-Fjords of Xorth Greenland and on the formation 

 of Fjords, Lakes, and Cirques in Xorwav and Greenland." Bv 

 M. A. Helland. 



The author described in great detail his observations on the 

 glacial phenomena of Greenland, and applied their results to the 

 consideration of the traces of glacial action exhibited in Norway. 

 He stated that the glacier of the Jacobshavn fjords, moving on a 

 slope of only |°, advances, at all events in summer, at from 14-20 

 to 19'77 metres per day, the maximum movement being about 

 64 feet per day. In all cases where the glaciers terminate in 

 fjords, and the formation of the latter is due to glacial action, it is 

 found that the mouth of the fjord is shallow, with an island or 

 islands bearing erratic blocks, whilst the interior is much deeper 

 even than the sea outside. The same characters are observed in the 



