31 
EMPLOYMENT OF THE LEVER FOR WORKING THE PRESS. 
the latter ; and it is drawn from under the 
platten by a small knob, represented at O 
IVI is the tympan, and N the jrisket, attached 
to the box in the usual manner. P is the 
inlciny -table ^ composed of a plate of cast- 
iron, imbedded in a frame of wood. It is 
fixed to the frame A by two thumb-screws. 
When not in use these screws are with- 
drawn, and the table turned round and 
pushed into a groove fitted to receive it, 
where it is again secured by the same 
screws. At A is a drawer for holding 
furniture, &c. At E is a weight to raise the 
platten after the pressure has been given, 
and keep it suspended. The part D C, of 
the lever D E, should be of such a length, 
as, when brought into a horizontal position, 
not to extend beyond the end of the frame 
A ; otherwise, when a heavy pressure is 
applied atD, the whole will be liable to be 
overturned. In the present case, D C is 16 
inches long. . The height of the cheeks B B 
should be such that the requisite pressure 
may be given a little before D E comes into 
a horizontal position. Any small error in 
this respect may be rectified by either plan- 
ing down, or pasting folds of paper upon 
the bottom of the box L. 
It will be observed, that the object gained 
by the employment of a lever, in the position 
described above, for working the press, is 
portability, as in any other position olf the 
lever the press would require to be fixed. 
The mode of operation of this press will 
now, I believe, be tolerably clear ; yet, to 
prevent misconception, I shall endeavour 
briefly to describe it. We shall suppose the 
matter locked up in the chase, or box, L, 
and the inking-tahle secured in its proper 
situation for working. The first thing to be 
done is, 'to put a little ink upon the table. 
Having distributed this equally vvith the 
roller, the workman lifts the tympan and 
frisket, and passes the roller over the face 
of the types in the usual manner. A piece 
of paper is then put upon the tympan, and 
this, together with the frisket, turned down 
upon the types The box is now pushed 
under the platten, and the lever pulled down 
till brought to a stop by the screw A. The 
lever is again raised, and the box withdrawn 
by the knob O. This process is to be repeat- 
ed till the number of impressions required 
are obtained. 
Resuming the expression (4), and fig. 
1, we find the following value of W, 
BA 1 
W = P X X 
B C (tan B D C -I- tan C B D) cos C B D. 
BA 16 32 
Now, here = — — — = 10-66, and we 
BC 3 
may^jassume for P what we please, ^’he 
last factor, therefore, is the only variable 
one, and its valuation depends solely on that 
of the angle C B D, or A B A . the other 
angle , B D C, being a function of this, and 
of the sides, B C, CD, which are given, and 
equal to 1^ and 3^ respectively. If, there 
fore, we wish to ktiow the actual power 
of this press, and also the increase of 
power consequent upon a diminution of the 
angle A B A or C B D, we shall have to sub- 
stitute in the above expression the values of 
BA 
P and for these quantities, and like- 
BC 
wise to give successive value to C B D. 
The results will be the values of W, or 
the power exerted by the press, for each 
particular value of the angle CBD ; and the 
differences of these results will be the in' 
crease corresponding to each diminution of 
that angle respectively. However, as W 
varies,/or the same value of C B D, directly 
as P, it is evident, that if we call P, 1 
pound, we shall be able, simply by multi- 
plying the value of W, obtained on that 
supposition by any number assumed for P, 
to find the value of W corresponding to that 
value of P. Calling P 1 pound, then, and 
B A 
substituting for its 
BC 
value, the expression becomes, 
1066 
W= 
(tan B D C + tan C B D) cos CBD. 
The following table exhibits, in the first 
column, a few assumed values of the angle 
CBD, decreasing by 5®, except in the last 
case, where the decrease is only 2° ; in the 
second, the value of W corresponding to 
these values of C B D, when p 1 pound ; 
and in the third, the increase of the power 
per cent., consequent upon each diminution 
of the aforesaid angle. 
Values of 
CBD 
Values of W. 
in Pounds. 
Increase 
Per Cent. 
250 
18-03 
20® 
22*14 
22* 8 
15® 
29*07 
31* 3 
100 
42*16 
45*03 
5® 
85-61 
103- 3 
3" 
226*18 
164* 2 
&c. 
&c. 
&c. 
We here see that while when, C B D is 
25®, a diminution of 5® occasions in an in- 
crease in the value of W of22’8 percent.; a 
diminution of only 2®, when C B D is 5®, 
occasions an increase in that value of no less 
than 164.2 per cent. Also, if we desire to 
know the absolute power of the press when 
