398 Magnetism of the Earth. 



" Treatise on the motion and measurement of Waters," by this cele- 

 brated painter. The treatise is inedited, and is said to be very re- 

 markable for its scientific accuracy, bearing the impress of its author, 

 who knew so well how to seize vipon and faithfully describe the ob- 

 jects upon which he fixed his attention. The manuscript was com- 

 posed about the year 1500, and had it been published, it would have 

 hastened the progress of Hydraulics. It is said to have been Leo- 

 nardi da Vinci who first ascribed the faint appearance of the dark 

 part of the moon, soon after the change, to the reflected light of the 

 earth.— Bib. Univ. Mars, 1830. 



Oolite in Sitii, in Edenville, Orange Co. N. Y. — In digging for 

 water in this village, a stratum of rock was encountered, fourteen feet 

 from the surface, dipping about 45° to the north-west, which being 

 blown through, proved to be four feet thick : the upper surface of 

 this stratum is oolite, well characterized, to the depth of twelve inch- 

 es ; after which it gradually passes into compact blue lime-rock. Be- 

 low this stratum no rock appeared for the depth of fifteen feet. 



Edenville stands upon the secondary blue lime-stone formation, 

 one-eighth of a mile from the eastern side of the range of primitive 

 %vhite lime-rock. J. P. Young. 



Hints and Conjectures respecting some of the Causes of the Earth'' s 

 Magnetism ; hy B. F. Joslin, M. D. Prof, of Math, and Nat. Phil, 

 in Union College, in a letter to the Editor.* 



The magnetism of the earth may arise from its motion on its axis, 

 and the situation of the poles is such as it should be if a current of 

 electricity passed around the earth from east to west. For when 

 electricity is made to pass round a needle by means of a spiral wire, 

 the end of the needle nearest the zinc end of the battery, or source 

 of the electricity, becomes the north pole when the spiral turns from 

 left to right, according to Mr. Van Beck, or, according to Mr. Bowen, 

 it acquires south polarity. There is no discrepancy in these two 

 results, as has been erroneously supposed. It should be remembered 

 that the north pole of a needle has south polarity, for opposite poles 

 attract each other. 



* This communication ought to have been inserted earlier, but was delayed by 

 accident. 



