1866.1 299 [Cresson. 



Royal Society at Upsal, October 1st, 1865 ; K. K. Geogr. 

 Reichs., Wcin, September 22d, 1865; K. K. Geo!. Gesell. 

 Wein, October 10th, 1865; Royal Lombardy Institute, 

 Milan, December 1st, 1862, August 27th, 1863; Linnean 

 Society, London, July 26th, 1865 ; Society of Antiquaries, 

 London, December 22d, 1865; American Antiquarian So- 

 ciety, Boston, January 11th, 1866 ; Corp. Yale College, New 

 Haven, January 13th, 1866; Lyceum Natural History, New 

 Jersey, January 10th, 1866 ; New Jersey Historical Society, 

 Newark, January 5th, 1866; Academy of Sciences, St. Louis, 

 December 23d, 1865. 



Donations for the Library were announced from the Lon- 

 don Linnean Society ; the Trinity College Observatory, 

 Dublin ; Dr. Lloyd ; the Boston Public Library ; Silliman's 

 Journal ; Blanchard & Lea ; the Franklin Institute ; and Mr. 

 Matthew Ryan, of Washington. 



Mr. Cresson gave an account of a recent useful application 

 of the principle of dia-magnetism first noticed by Faraday in 

 1845 at the close of his extended series of Experimental Re- 

 searches in Electricity, but remaining unapplied and almost 

 unnoticed for nearly twenty years. 



According to Faraday's report to the Royal Society the force 

 termed dia-magnetic gives rise to a repellant action between a mag- 

 net and various bodies previously supposed destitute of magnetic 

 relations. This property was found in vegetable, animal, and earthy 

 substances. 



One of the phenomena exhibited in his experiments on these 

 bodies is a discrimination in the attraction or repulsion exerted by a 

 magnet, between substances placed near it in liquid suspension so as 

 to be capable of free motion. The discriminating action is governed 

 by the relative degree of repellant or attractive power belonging to 

 the different bodies. 



A result of this discrimination is to cause the particles most feebly 

 repelled or most strongly attracted to come between the magnet and 

 such other particles as are more strongly repelled or more feebly 

 attracted ; thus making the particles most feebly aflPected either by 

 attraction or repulsion behave as if they belonged to the opposite 

 magnetic class. 



The practical use now made of this principle consists in imparting 



