I lately acquainted you, that I had been able to fire Spirit of Wine,
_Phlogiston_ of _Frobenius_, and common proof Spirit, by the Power of
Electricity. Since which (till Yesterday) we have had but one very dry
fine Day; _viz._ _Monday, April 15_. Wind E. N. E.; when about four
o'Clock in the Afternoon, I got my _Apparatus_ ready, and fired the
Spirit of Wine four Times from the Poker as before, three Times from the
Finger of a Person electrified, standing upon a Cake of Wax, and once
from the Finger of a second Person standing upon Wax, communicating with
the first by means of a walking Cane held between their Arms extended.
The horizontal Distance in this Case between the glass Tube and the
Spirit was at least ten Feet.
YOU all know, that there is the repulsive Power of Electricity, as well
as the attractive; inasmuch as you are able, when a Feather or such-like
light Substance is replete with Electricity, to drive it about a Room,
which Way you please. This repulsive Power continues, until either the
Tube loses its excited Force, or the Feather attracts the Moisture from
the Air, or comes near to some non-electric Substance; if so, the
Feather is attracted by, and its Electricity lost in, whatever
Non-Electric it comes near. In electrified Bodies, you see a perpetual
Endeavour to get rid of their Electricity. This induced me to make the
following Experiment. I placed a Man upon a Cake of Wax, who held in one
of his Hands a Spoon with the warm Spirits, and in the other a Poker
with the Thread. I rubbed the Tube amongst the Thread, and electrified
him as before. I then ordered a Person not electrified to bring his
Finger near the Middle of the Spoon; upon which, the Flash from the
Spoon and Spirit was violent enough to fire the Spirit. This Experiment
I then repeated three Times. In this Method, the Person by whose Finger
the Spirit of Wine is fired, feels the Stroke much more violent, than
when the electrical Fire goes from him to the Spoon. This Method for the
Sake of Distinction, we will call the repulsive Power of Electricity.
THE late Dr. _Desaguliers_ has observed in his excellent Dissertation
concerning Electricity, "That there is a Sort of Capriciousness
attending these Experiments, or something unaccountable in their
Phænomena, not to be reduced to any Rule. For sometimes an Experiment,
which has been made several Times successively, will all at once fail."
Now I imagine that the greatest Part, if not the Whole of this Matter,
depends upon the Moisture or Dryness of the Air, a sudden though slight
Alteration in which, perhaps not sufficient to be obvious to our
Faculties, may be perceived by the very subtle Fire of Electricity. For
_1st_, I CONCEIVE, that the Air itself (as has been observed by Dr.
_Desaguliers_) is an _Electric per se_ and of the vitreous Kind;
therefore it repels the Electricity arising from the glass Tube, and
disposes it to electrify whatever non-electrical Bodies receive the
Effluvia from the Tube.
_2dly_, THAT Water is a _non-Electric_, and of Consequence a Conductor
of Electricity; this is exemplified by a Jett of Water being attracted
by the Tube, _from either Electric_'s _per se_ conducting Electricity,
and _non-Electric_'s more readily when wetted; but what is more to my
present Purpose, is, that if you only blow through a dry glass Tube, the
Moisture from your Breath will cause that Tube to be a Conductor of
Electricity.
THESE being premised; in proportion as the Air is replete with watery
Vapours, the Electricity arising from the Tube, instead of being
conducted as proposed, is, by means of these Vapours, communicated to
the circum-ambient Atmosphere and dissipated as fast as excited.
THIS Theory has been confirmed to me by divers Experiments, but by none
more remarkably than on the Evening of the Day I made those
before-mention'd; when the Vapours, which in the Afternoon by the Sun's
Heat, and a brisk Gale were dissipated, and the Air perfectly dry,
descended again in great Plenty upon the Absence of both, and the
Evening was very damp. For between seven and eight o'Clock, I attempted
again the same Experiments in the same Manner, without being able to
make any of them succeed; though all those mention'd in this Paper with
others of less Note, were made in Half an Hour's Time.
I AM the more particular in this, being willing to save the Labour of
those, who are desirous of making these Kind of Trials; for although
some of the lesser Experiments may succeed almost at any Time, yet I
never could find that the more remarkable ones would succeed but in dry
Weather.
_I am, Gentlemen,_
_Your most obedient,_
_humble Servant,_
W. WATSON.
_London, April
25. 1745._
[Illustration]
TO THE
ROYAL SOCIETY.