RET 
lated stool, touch this second conductor 
very lightly with a finger of his right hand ; 
■while with a finger of hiS left hand he com- 
municates with the earth, by touching very 
lightly a second brass ball, fixed at the top 
of a metallic stand, on the floor, which may 
be called B. Now, while the prime con- 
ductor is receiving its electricity, sparks 
pass (at least if the distance between the 
two conductors is not too great) from the 
second conductor to the right hand of the 
insulated person ; while similar and simul- 
taneous sparks pass out from the finger of 
his left hand into the second metallic ball, 
B, communicating with the earth. At 
length, however, the prime conductor, hav- 
ing acquired its full charge, suddenly strikes 
into the ball, A, of the first metallic stand, 
placed for that purpose at the striking dis- 
tance. The explosion being made, and the 
prime conductor suddenly robbed of its 
elastic atmosphere, its pressure or action 
on the second conductor, and on the insu- 
lated person, as suddenly ceases, and the 
latter instantly feels a smart returning 
stroke, though he has no direct or visible 
communication (except by the floor) with 
either of the two bodies, and is placed at 
the distance of five or six feet from. both of 
them. This returning stroke is evidently 
occasioned by the sudden re-entrance of 
the electric fire naturally belonging to his 
body and to the second conductor, which 
had before been expelled from them by the 
action of the charged prime conductor upon 
them ; and which returns to its former 
place in the instant when that action or 
elastic pressure ceases. When the second 
conductor and the insulated person are 
placed in the densest part of the electrical 
atmosphere of the prime conductor, or just 
beyond the striking distance, the effects 
are stii! more considerable ; the returning 
stroke being extremely severe and pun- 
gent, and appearing considerably sharper 
than even the main stroke itself received 
directly from the prime conductor. Lord 
Mahon observes, that persons and animals 
may be destroyed, and particular parts of 
buildings may be much damaged, by an 
electrical returning stroke, occasioned even 
by some very distant explosion from a thun- 
der cloud ; possibly at the distance of a 
mile or more, ft is certainly hot difficult 
to conceive, that a charged extensive thun- 
der cloud must be productive of effects si- 
milar to tlsose produced by the prime con- 
ductor ; but perhaps the effects are not so 
|;reat, nor the danger so terrible, as it seems 
REV 
to have been apprehended. If the quantity 
of electric fluid naturally contained, for ex- 
ample, in the body of a man, were immense 
or indefinite, then the estimate between 
the effects producable by a cloud, and those 
caused by a prime conductor, might be ad- 
mitted ; but surely no electrical cloud can 
expel from a body more than the natural 
quantity of electricity which this contains. 
On the sudden removal, therefore, of the 
pressure by which this natural quantity had 
been expelled, in consequence of the ex- 
plosion of the cloud into the earth, no more 
(at the utmost) than his whole natural stock 
of electricity can re-enter bis body, pro- 
vided it be so situated, that the returning 
fire of other bodies must necessarily pass 
through his body. But perhaps we have 
no reason to suppose, that this quantity is 
so great, as that its sudden re-entrance into 
his body should destroy or injure him. See 
“ Mahon’s Electricity.” 
RETZIA, in botany, so named in honour 
of Anders Jahan Retzius, Professor of Na- 
tural History ; a genus of the Pentandria 
Monogynia class and order. Natural or- 
der of Cainpanaceae. Convolvuli, Jussieu. 
Essential character : corolla cylindrical, 
villose on the outside ; stigma bifid ; cap- 
sule two-celled, many seeded. There is 
but one species, viz. R. spicata ; it is found 
on the highest mountains, near the Cape of 
Good Hope. 
REVENUE, puJKc, the portion of the 
general income of a state, which is appro- 
priated to the payment of national ex- 
penses, Different nations have adopted 
different modes of raising a public revenue, 
but the rent derived from land being ob- 
viously a fund of a more permanent nature 
than most others, has usually been one of 
the earliest resources, and has sometimes 
been the principal souice of public re- 
venue, particularly in ancient limes. From 
the produce or rent of the public lands, the 
republics of Greece and Italy derived, for 
a long time, the greater part of the revenue 
which defrayed the necessary expenses of 
the commonwealth ; and the rent of the 
crown-lands constituted the greater part of 
the revenue of the ancient sovereigns of 
Europe. The intfoduction of a different 
mode of warfare, and the greater duration 
of modern wars, increased considerably the 
public expenditure, and rendered it neces- 
sary to raise a much greater revenue. Ii} 
the ancient republics of Greece and Italy, 
every citizen was a soldier, who both pre- 
pared himself for service, and served af his 
