56 Machine for Microscopic Writing. 
the height of the letters is 1-10,000 of a linear inch, so that 
the space occupied by the letters a or n, or such as are about 
as wide as they are high, is no more than l-100,000,000th, 
the hundred millionth of a square inch. 
In examining the construction of the machine, it will be 
convenient to consider, ^r.s^. The Frame or Stand, and then 
THE Mechanism ; referring in succession to (1) the arrange- 
ments for transmitting and diminishing motion; (2) those for 
controlling and directing the movements ; (3) and lastly, the 
contrivances for preserving traces of those movements which it 
is wished to record, so that they may be viewed with the 
microscope. 
The Stand. A rectangular table of mahogany, 18 in. by 
10 in. superfices, and about an inch thick, constitutes the base 
{A) ; to the surface of this is fastened a stout plate of brass, 
of nearly the same size (B) ; near each corner of this is fixed 
a brass column (C), a little more than an inch diameter, and 
31 inches high. The four^folumns support a stout brass plate 
(jD), 15 in. by 7J in., on which stand four smaller columns 12 
inches high (E), they support another stage (F) 10 in. by 4 
in., to which the principal part of the mechanism is attached. 
The Mechanism : First Machine constructed in 1852. In 
the simplest form of the machine, a vertical rod connected 
near its superior extremity {G, fig. 1), with the upper brass 
plate (F, fig. 1), and extending from it nearly to the base, 
constitutes a simple lever of the first kind {G H, fig. 1), 
whose arms are in the ratio of 1 : 125 nearly. The rod tapers 
downwards, its diameter diminishing from an inch to a quarter 
of an inch, or thereabouts : this form of rod has been found 
the most steady and least liable to tremor. It is connected 
with the upper stage (jP) by means of two concentric rings: 
the outer one (/) is firmly fixed to the brass plate : the inner 
one (J) is connected by horizontal pivots with the outer ring, 
and with the vertical rod {G); the axes of the two pairs of 
pivots being at right angles to one another : by this connexion 
rectilinear motion in one direction is permitted by the move- 
ment of the rod (G) on the pivots of the inner ring {J), a 
similar motion at right angles to this is effected by the move- 
ment of the inner ring (J) on the pivots of the outer one (/) ; 
by a combination of movements determined by the two axes, 
motion in any direction, rectilinear or curved, is attainable. 
Every movement of the lower end of the rod (j^) is repeated 
by the other end {G), diminished in extent, and reversed in 
direction. With a machine thus constructed, the diminishing 
power is about 125 times, linear ; that is to say, a line one inch 
in length traced by the lower end of the rod, will give at the 
