OF ARTS AND SCIENCES. 105 



Three hundred and twelfth meeting. 



November 14, 1848. — Monthly Meeting. 



The President in the chair. 



Colonel Graham, of the U. S. Topographical Engineers, gave 

 an account of the labors of the commissioners for running the 

 boundary between the United States and Canada, as estab- 

 lished by the Treaty of Washington, and stated that the maps,* 

 which were destroyed by fire at Washington when nearly 

 completed, were now in course of reconstruction from the 

 field-notes, &c., copies of which, by direction of the govern- 

 ment, were deposited in different places, so as to guard against 

 their destruction by fire, or other casualty. 



Professor Webster exhibited remarkably fine specimens of 

 beryl from Royalton, and idocrase from Sanford, near Wells, 

 Maine. 



Mr. Desor made some remarks on the retrogression of Ni- 

 agara Falls, illustrated by plans, and gave reasons for believ- 

 ing that, in their future retrogression, the gradual diminution 

 in the height of the cataract which has been taught by other 

 geologists would not take place. 



Professor Levering read a paper on the causes of the re- 

 markable differences in the strength of ordinary magnets and 

 electro-magnets of the same shape and size, as follows : — 



" It is well known that the strength of ordinary magnets does not 

 increase in the same proportion as their weight ; but much more slowly. 

 For example, a magnet weighing only three grains has lifted two hun- 

 dred and fifty times its own weight. A magnet weighing twenty-five 

 grains sometimes lifts forty-five times its own weight. Peschel's new 

 method of magnetizing is consiaered very efficient, because it will give 

 to a magnet which weighs one pound the power to lift about twenty-six 

 pounds. Magnets of two pounds' weight will rarely lift ten times their 

 own weight. A magnet in the possession of Mr. Peale, of Philadel- 

 phia, (the largest natural magnet known,) weighs fifty-two pounds and 

 lifts three hundred and ten pounds ; that is, only six times its own 

 weight. These cases are not strictly comparable, because the shape 

 and quality of the iron are not the same in all of them. They indi- 



voh. II. 14 



