EXCITATION OF ELECTRICITY BY STEAM AND WATER. 
19 
resin before the valve was opened, the opening 1 of the valve and consequent evapora- 
tion did not affect this charge. Again, having 1 obtained the power of constructing 
steam passages which should give either the positive or the negative, or the neutral 
state (2102. 2110. 2117-)> I could attach these to the steam way, so as to make the 
boiler either positive, or negative, or neutral at pleasure with the same steam, and 
whilst the evaporation for the whole time continued the same. So that the excitation 
of electricity is clearly independent of the evaporation or of the change of state. 
2084. The issue of steam alone is not sufficient to evolve electricity*. To illustrate 
this point I may say that the cone apparatus (20 77-) is an excellent exciter : so also 
is a box-wood tube (2102. fig. 5.) soaked in water, and screwed into the steam-globe. 
If with either of these arrangements, the steam-globe (fig. 1.) be empty of water, so 
as to catch and retain that which is condensed from the steam, then after the first 
moment (2089.), and when the apparatus is hot, the issuing steam excites no electri- 
city ; but when the steam-globe is filled up so far that the rest of the condensed 
water is swept forward with the steam, abundance of electricity appears. If then the 
globe be emptied of its water, the electricity ceases ; but upon filling it up to the 
proper height, it immediately reappears in full force. So when the feeder apparatus 
(2078.) was used, whilst there was no water in the passage-tube, there was no elec- 
tricity ; but on letting in water from the feeder, electricity was immediately evolved. 
2085. The electricity is due entirely to the friction of the particles of water which 
the steam carries forward against the surrounding solid matter of the passage, or 
that which, as with the cone (20/7.); is purposely opposed to it, and is in its nature 
like any other ordinary case of excitement by friction. As will be shown hereafter 
(2130. 2132.), a very small quantity of water properly rubbed against the obstructing 
or interposed body, will produce a very sensible proportion of electricity. 
2086. Of the many circumstances affecting this evolution of electricity, there are 
one or two which I ought to refer to here. Increase of pressure (as is well illustrated 
by Mr. Armstrong’s experiments) greatly increases the effect, simply by rubbing the 
two exciting substances more powerfully together. Increase of pressure will some- 
times change the positive power of a passage to negative ; not that it has power of 
itself to change the quality of the passage, but as will be seen presently (2108.), by 
carrying off that which gave the positive power; no increase of pressure, as far as I 
can find, can change the negative power of a given passage to positive. In other 
phenomena hereafter to be described (2090. 2105.), increase of pressure will no doubt 
have its influence ; and an effect which has been decreased, or even annihilated (as 
by the addition of substances to the water in the steam-globe, or to the issuing cur- 
rent of water and steam), may, no doubt, by increase of pressure be again developed 
and exalted. 
2087- The shape and form of the exciting passage has great influence, by favouring 
* Mr. Armstrong has also ascertained that water is essential to a high development. Phil. Mag. 1843, 
vol. xxii. p. 2. 
