THE BAROMETER AND THE WEATHER. 181 



flow of water upon my supposed submarine bed of till just 

 grazing the bottom of the glacier ? Obviously to wash away 

 the fine clayey particles, and leave behind the coarser sand or 

 gravel. It must form just such a basin or lenticular cavity as 

 Mr. Geikie describes. The oblong shape of these, their longer 

 axis coinciding with the general course of the glacier, would 

 be produced by the onward progress of the moulin. The 

 accordance of their other features with this explanation will be 

 seen on reading Mr. Geikie's description (pp. 18,19, etc.). 



The general absence of marine animals and their occasional 

 exceptional occurrence in the intercalated beds is just what 

 might be expected under the conditions I have sketched. In 

 the gloomy subglacial depths of the sea, drenched with continual 

 supplies of fresh water and cooled below the freezing-point by 

 the action of salt water on the ice, ordinary marine life would 

 be impossible ; while, on the other hand, any recession of the 

 glacial limit would restore the conditions of arctic animal life, 

 to be again obliterated with the renewed outward growth of 

 the floating skirts of the inland ice-mantle. 



But I must now refrain from the further discussion of these 

 and other collateral details, but hope to return to them in 

 another paper. 



In " Through Norway with Ladies" I have touched lightly 

 upon some of these, and have more particularly described some 

 curious and very extensive evidences of secondary glaciation 

 that quite escaped my attention on my first visit, and which, 

 too, have been equally overlooked by other observers. In the 

 above I have endeavored to keep as nearly as possible to the 

 main subject of the origin of the till and the character of the 

 ancient ice-sheet. 



CHAPTER XXIV. 



THE BAROMETER AND THE WEATHER. 



THE barometer was invented by Torricelli, an Italian philos- 

 opher of the seventeenth century. It consists essentially of a 

 long tube open at one end and closed at the other, and partly 

 filled with mercury ; but instead of being filled like ordinary 

 vessels, with the open end or mouth upward and the closed 



