MachiiLe for Microscopic Writing. 59 
for the first {H K : K O), and 9 ; 1 for the second {O G : G Z), 
will diminish 108 times linear ; an arrangement in which the 
arms of the first lever are in the ratio of 500 : 1, and those of 
the second as 12 : 1, will have the power of diminishing 6,000 
times linear ; and though it is not easy to determine exactly by 
measurement the effective length of the different members of 
the combination, it is believed that these proportions are not 
far from the truth. By these adaptations, the transmission 
and diminution of motion are provided for. 
Contrivances for controlling and directing the movements^ are 
next to be noticed. It is manifest that the free end (H) of a 
lever suspended in the way described would move in the arc 
of a circle : to obviate the inconvenience of writing on a con- 
cave surface, and at the same time to provide for a greater 
freedom of motion to the pen or pencil, the lever is continued 
to the surface of the base of the stand by means of a rod {S), 
which passes into the lower end of the suspended tube (^), 
and is connected with a second short rod {T U) by two pairs 
of rings ( V)f each pair joined together in one plane, and all 
moving on horizontal pivots, so as to maintain exact parallelism 
of the two rods, while the second one (T* U) is allowed to 
move freely in a vertical direction : the second rod has at its 
lower end a joint ( Z7), connecting it with a short arm which 
carries a split tube (fV) for holding a pen (X) or pencil ; by 
means of this joint the pen may be made to have any inclina- 
tion from the perpendicular; an adjustment in azimuth may 
be made by turning the rod {S) in the vertical tube {JI) : it 
may be fixed in any position by a screw ( J^) brought to press 
against it : this arrangement allows the pencil to move freely 
over every part of a surface of about 5 inches square, within 
which space it is perfectly under control, and on the surface of 
which any writing or design may be conveniently traced. 
A brass frame about 5 inches square is attached to the centre 
of the plate which covers the base of the stand, by four screws 
with milled heads, one at each corner ; after loosening these 
screws, a card may be placed under the frame, and the screws 
being then tightened, it is held firmly in its place without any 
further attention on the part of the person using the machine. 
Registry of the diminished design. — ^Tracings of the dimi- 
nished movements are received on glass, that material afford- 
ing the greatest facilities for the use of the microscope in 
examining them. The distal extremity of the combined levers 
is therefore armed with a diamond point, and in order that it 
may act upon the upper surface of the glass, tlie vertical rod 
is connected with one end of a horizontal arm (A), from the 
other end of which a piece (^/) at right angles to it rises to 
