13 



remarked upon the value and rarity of the instrument, and gave an 

 account of its history and use. The chair also read a note from JOHN 

 H. SEARS, of Danvers, stating that several Hawks and Owls had com- 

 menced building their nests. The chair also called attention to sev- 

 eral hymn and other books in possession of Capt. DAY, of Salem. 



Mr. GEORGE L. VOSE of Paris, Me., was introduced and gave an ac- 

 count of the formation of glaciers. The following is a brief extract 

 of his remarks : 



The existence of the glaciers depends upon the occurrence, in cer- 

 tain parts of the earth, of large masses of perpetual snow. The first 

 question then to be answered, in the study of the glaciers in their 

 physical aspect, is, what are the conditions under which snow lies 

 upon the ground summer and winter, year after year; in fine, what is 

 the cause of perpetual snow? In the common course of nature the 

 water which falls from the clouds is disposed of in three ways : by 

 sinking into the ground, by evaporating from the surface, and by 

 flowing off from the higher to the lower lands in the form of rivers, 

 by which it is carried to the sea; from the sea it is evaporated, to 

 be condensed into rain and again thrown down upon the surface of 

 the earth. But in order that this circulation may go on, the water 

 must remain in the liquid form, it must be water. Below a certain 

 temperature water becomes ice, and whatever moisture falls from the 

 clouds, falls not as rain, but as snow, or hail or ice. The higher re- 

 gions of the atmosphere are in a great degree deprived of the solar 

 heat reflected from the earth, and enjoy only the direct heat from the 

 sun, which is not enough to keep water in the liquid form. What then 

 becomes of the snow which falls upon high mountains, where it is so 

 cold that it cannot melt, and thus cannot escape in any of the methods 

 employed for the circulation of water ? Why does it not accumulate 

 indefinitely upwards until the whole country is buried in everlasting 

 snow ? This question is answered by the existence and operation of 

 the glaciers. At its upper end a glacier is snow ; this snow is very 

 gradually compacted into an immense river of ice, which forced along 

 by the subsiding and pressing out laterally of the great mass of uncon- 

 solidated snow at the upper end, moves at the rate of from one to two 

 feet in a day, and thus draws the snow off in a solid form from a high 

 cold region where it could never melt so as to soak into the ground, 

 or evaporate, or flow off to the ocean, and leads it down to a low 

 warm region where it melts, and giving birth to a stream of water 

 flnds its way 'to the ocean, thus completing the circulation of moisture 

 above referred to. 



It is at first sight difficult to understand how ice can move through 

 a long winding valley over all the roughness of the ground. Prof. 

 Tyndall, however, has shown that the hardest ice, under certain con- 

 ditions, behaves as a plastic mass. He actually moulded cubes of 

 brittle ice into rings, spheres and other figures. The requisite condi- 

 tions are pressure and time ; immense compression, applied in a very 

 gradual manner, forces the huge mass of the glacier along the wind- 

 ings of the valley, around the mountain spurs ; welds together several 

 tributaries into a main trunk, and gives to the whole mass a motion 

 of precisely the same quality, though far less in velocity, as that of a 

 river of water. 



The great weight of the moving ice produces an effect upon the 

 rocks and the ground over which it passes, which is not only of inter- 



