IV. MAGNETISATION. 243 



1125g. Electro- Magnetic Engine, patented by Thomas 

 Allan, No. 14,190, A.D. 1852; and No. 2,243, A.D. 1854. 



Lent from the Patent Office Museum by the Commissioners 

 of Patents. 



This engine is so constructed that when set in action several electro- 

 magnets are formed one after the other, and give successive impulses in the 

 same line or direction to an upright rod or bar, capable of being moved longi- 

 tudinally to any desired extent. 



1125h. Electro-Magnetic Machine, Invented by Sir Charles 

 Wheatstone. 



Wheatstone Collection of Physical Apparatus, King's 

 College, London. 



1 1251. Electro-Magnetic Machine, invented by Sir Charles 

 Wheatstone. 



Wheatstone Collection of Physical Apparatus, King's 

 College, London. 



IV. APPARATUS FOR INVESTIGATIONS CONNECTED 

 WITH PHENOMENA OF MAGNETISATION. 



1126. Apparatus showing a remarkable property of 

 magnetised Soft Iron Tubes. 



Professor Dr. A. von Waltenhofen, Prague. 



On a balance are suspended a tube and a solid cylinder, both of soft iron, 

 the cylinder being much heavier, and therefore counterbalanced by adding a 

 brass weight to the tube, or by filling it with shot. Both tube and cylinder 

 are introduced into an electro-magnetic helix, fixed upright beneath the 

 balance at the bottom of the apparatus (as in the electro-magnetic balance of 

 Becquerel). The coils are joined so as to unite the poles of a Bunsen's cell, 

 or any other voltaic cell of unimportant resistance. 



On completing the circuit, a suction force is exerted on the tube and the 

 cylinder, tending to draw them into the helices. The tube or cylinder will 

 then appear the heavier, according as the electric current possesses less or 

 more strength. This change can be performed at pleasure by means of a 

 Wheatstone's rheostat, introduced in the path of the current. 



The theory of this phenomenon is given in the Sitzungsberichte d. k. 

 Akademie d. Wissenschaften. Juli Heft, 1870. 



1126a. Apparatus by Mr. Th. Petroucheffsky, Professor at 

 the University of St. Petersburg, for measuring the distance of 

 the Magnetic Poles in straight magnets from their ends. 



Imperial University of St. Petersburg. 



point where one of the 



, , 



to the suspended needle. A slow movement can be given to this second 

 magnet along a divided rule, horizontal and parallel to the suspended needle. 



Q 2 



