80 Prof. J. A. Fleming on the 



in proportion as the collecting-plate is larger and in propor- 

 tion as it is brought into close proximity to the base of the 

 negative leg of the carbon. Also that a plate so placed is 

 brought down to the potential of the negative electrode. ^ It 

 seemed desirable to see how far the removal of the collecting- 

 plate to a great distance from the negative leg would influence 

 these results, and experiments were accordingly tried with a 

 tube of the form shown in fig. 11. 



Experiment 12. — In this case a glass tube about eighteen 

 inches long and three-quarters of an inch in diameter was 

 attached to a lamp bulb. The end of the glass tube furthest 

 from the bulb was closed and an aluminium plate welded to a 

 platinum wire was sealed in near this closed end. The plate 

 had a length of about 3 centimetres and a wudth of about 

 1 centimetre. The tube formed an extension of the bulb- 

 space, and accordingly this arrangement formed a device by 

 which a metal plate could be removed to a distance of some 

 eighteen inches from the incandescent conductor contained in 

 the bulb. On placing this lamp on a circuit and bringing 

 the carbon to normal incandescence and connecting the ter- 

 minals of the Elliott galvanometer respectively to the aluminium 

 plate and the positive electrode of the lamp, a very small 

 current was found to be passing through it, not, however, 

 exceeding one ten-thousandth of a milliampere. When the 

 galvanometer was joined in between the aluminium plate and 

 the negative leg of the carbon no current whatever could be 

 detected with this galvanometer, which was sufficiently sensitive 

 to show one hundred-thousandth of a milliampere. We thus 

 find that the removal of the plate to a distance of some 



