Lecture on a new property of Magnetism. 535 



effects. I am able te shew you air or vacuum either magnetic or 

 diamagnetic at pleasure. When I put substances between the two 

 poles of the magnet, in order to examine their properties, I must not 

 forget their nature. When I am examining bismuth there is air 

 all around it ; if it had power it might influence it, but it has 

 not. If, however, I put iron, nickel, cobalt, or water, I find the 

 medium between the two poles, and which is the magnetic field, has 

 a strong action. Here is a jar partly filled with a solution of iron, 

 and partly with water. [The water was floating on a saturated 

 solution of green sulphate of iron.] There is a separation about the 

 middle ; it is occasioned only by the difference of gravity ; it is one 

 jar of liquid, but the lower part is iron, the upper water. The weak- 

 est solution of iron is magnetic ; water is diamagnetic ; therefore I 

 have two liquids, which, if I put in this place, I can make the 

 medium through which the lines of magnetic force will act. You 

 see that part of the space between these two points is now occupied 

 by water ; and if I raise up this jar and put a board under it, the 

 space occupied between the poles will then be a portion of the solu- 

 tion of iron. I am now about to show you, that the tube of air will 

 appear magnetic, or diamagnetic just as it happens to be immersed 

 in the water or in the ferruginous solution. As far as we know, the 

 air that surrounds our globe may have some remarkable relation to it 

 in regard to magnetism. I think this suspender seems nearly fitted 

 to take the tube, and carry it into the solution. First observe, it is 

 a tube of air sealed and sustained in a cradle of copper wire ; and 

 beneath the tube, at the middle part, I have placed a smaller tube 

 containing mercury, which serves for a counterpoise or ballast, to make 

 the tube descend into the solution or water, and keep it beneath the 

 surface. Then there is a card above, which, being parallel to the 

 tube itself, will shew you the position of the tube as respects the 

 place of the magnet. This is now suspended ; I am about to put it 

 in ; it will sink to pretty nearly the level I want ; if not, I can raise it 

 by bending the wire. The adjustment will bring it to the centre of 

 motion, and place it so that it is perfectly free to move in the jar. I 

 am taking the risk of the current of air in the room moving the 

 indicator, because I want every thing free, that you may comprehend 

 the beauty of the experiment. The tube of air is now free to move, 



