JOSEPH HENRY, LL.D. 83 



densed air, by means of a powerful condensing 

 pump, until the pressure was estimated at nine 

 atmospheres. During the condensation, the vessel 

 became sensibly warm. After suffering the appa- 

 ratus to cool down to the temperature of the room, 

 the stop-cock was opened : the air rushed out with 

 great violence, carrying with it a quantity of water, 

 which was instantly converted into snow. After a 

 few seconds, the tube became filled with ice, which 

 almost entirely stopped the current of air. The 

 neck of the vessel was then partially unscrewed, 

 so as to allow the condensed air to rush out around 

 the sides of the screw ; in this state the tempera- 

 ture of the whole interior atmosphere was so much 

 reduced as to freeze the remaining water in the 

 vessel." 



Other pamphlets followed this publication, but 

 in 1831 a notable paper in the " American Journal 

 of Science and the Arts " brought Henry's name to 

 the front line of discoverers in electro-magnetism. 

 Sturgeon made the first electro-magnet; Henry 

 made the electro-magnet what it is. 



Says W. B. Taylor, in an address before the 

 " Philosophical Society of Washington : " " The 

 electro-magnet figured and described by Sturgeon' 

 consisted of a small bar or stout iron wire bent into 

 a Q or horse-shoe form, having a copper wire wound 

 loosely around it in eighteen turns, with the ends 

 of the wire dipping into mercury-cups connected 

 with the respective poles of a battery having one 

 hundred and thirty square inches of active surface." 



