408 Dr. Faraday on the Diamagnetic conditions 



portant not to deluge the magnetic field with a quantity of in- 

 visible gas, I devised the following arrangement, which an- 

 swered well for all the gases not soluble in water. A WoulPs 

 bottle was chosen having three apertures at the top, a, h and c ; 

 a wide tube was fixed into aperture a, descending within the 

 bottle to the bottom, and being open above and below ; by 

 this any water could be poured into the bottle and employed 

 to displace the gas previously within it. Aperture b was closed 

 by a stopper. Aperture c had an external tube, with a stop- 

 cock fixed in it to conduct the gas to any place desired. To 

 expel the gas and send it forward, a cistern of water was placed 

 above the bottle, and its cock so plugged by a splinter of 

 wood, that when full open it delivered only twelve cubic inches 

 of fluid in a minute. This stream of water being directed into 

 aperture a, and the cock of tube c open, twelve cubic inches 

 of any gas within the Woulf's bottle was delivered in a minute 

 of time ; and this I found an excellent proportion for our mag- 

 net and apparatus. 



With respect to the delivery of this gas at the magnetic 



poles, a piece of glass tube bent into this shape j was held 



by a clamp on the stage of the magnet, so that it could easily 

 be slipped backward and forward, or to one side, and so its 

 vertical part be placed anywhere below the axial line. The 

 apertuie at this end was about the one-eighth of an inch in- 

 ternal diameter. In the horizontal part near the angle was 

 placed a piece of bibulous paper, moistened with strong solu- 

 tion of muriatic acid (when necessary). The horizontal part 

 of the tube was connected and disconnected in a moment, when 

 necessary, with the tube c of the gas-bottle, by a short piece 

 of vulcanized rubber tube. If the gas to be employed as a 

 stream were heavier than the surrounding medium, then the 

 glass tube, instead of having the form delineated above, was 

 so bent as to deliver its stream downwards and over the axial 

 line. In this manner currents of different gases could be de- 

 livered, perfectly steady and under perfect command. 



The next point was to detect and trace the course of these 

 streams. A little ammonia vapour, delivered near the mag- 

 netic field, did this in some degree, but was not satisfactory ; 

 for, in the first place, the little cloud of muriate of ammonia 

 particles formed, is itself diamagnetic ; and further, the tran- 

 quil condition of the air in the magnetic field was then too 

 much disturbed. Catch-tubes were therefore arranged, con- 

 sisting of tubes of thin glass about the size and length of a 

 finger, open at both ends, and fixed upon little stands so that 

 they could be adjusted either over or under the magnetic poles 

 at pleasure. When they were over the polesy I generally had 



