642 -WONDERS OF XRT. 
of rollers, the impression is taken on one side. The sheet 
is then conveyed off by bands to a second cylinder, aroui'^ 
which it is carried on the second form, and the reiteration i* 
produced in perfect register, without the aid of points. Al' 
the manual labour is performed by a boy, who lays the 
sheet of paper on the first cylinder, by one who takes )• 
off from the second cylinder, and by a third, who lays ih* 
sheets even on the bank. As a further instance of econoioy 
in the materials, we may mention, that the waste steanJ 
from the copper is earned in tubes round the entire suits 
of offices, with a view to warm them. 
GRAND GALVANIC BATTERY. 
To comprehend more precisely the astonishing powers 
this battery, prepared by Sir Humphrey Davy for the Abo* 
ratory of the Royal Institution, it is necessary to premis®> 
that the conductors of the galvanic fluid are divided int® 
perfect and imperfect,^ the former consisting of metallic 
substances and charcoal, and the latter of water and aV}“ 
dated fluids, as the acids and all the substances which coH’ 
tain these fluids. The simplest galvanic combinations musi 
consist of three difterent conductors, not wholly of ooe 
class. When two of tlie three bodies are of the first class> 
the combination is said to be of the first order ; wh®*' 
otherwise, it is said to be of the second. In simple g^' 
vanic circles it is indispensably requisite that the conducto'^ 
of one class .shall have some chemical action on those of 
other ; for example : if a piece of zinc be laid on a p'^c® 
of copper, and on the copper a piece of card or flanneh 
moistened with a solution of salt-water, a circle of the fir* 
class is formed ; and if three other pieces be then laid o'* 
these in the same order, and repeated several times, 
whole will form a pile, or battery, of the first order. 
the three bodies which form a galvanic circle of the 
order are laid on each other, the upper and the under on 
not touching, these two extremes are in opposite eleon 
otates. The galvanic eftects may be increased to any degf®®’ 
by a repetition of the same simple galvanic combination ; 
and these repeated combinations are called galvanic pn®® 
or batteries, which may be constructed of various forms. 
The grand galvanic battery, the most powein 
