DESCRIPTION OF A PORTABLE PRINTING PRESS. 
29 
of simplicity, cheapness, and portability; er, as the hand, be applied at A, so as to 
and having succeeded therein to the utmost bring B A into the position B A' (B A' be- 
extc-nt of my expectations, the following^ ing drawn at right angles to B D), it is plain, 
description may perhaps notbe unacceptable that the effect will be to bring B C and C D 
to your readers. I shall first explain the into the same straight line, and, consequently, 
principle I have employed, and then describe to depress D. 
the construction by which I have endea- To calculate the relation that subsists be- 
voured to adapt that principle to the purpose tween the power applied at A and the ulti- 
required. n>ate force exerted at D, produce D C to E, 
ABC, fig. 1, is a lever, bent into a right and let fall B E perpendicular thereto, 
angle at B, at which point it moves on an Now, calling the forces at A, C, and 
axis as a fulcrum. To the extremity, C, a D, P, P', and W, respectively, we have, 
p : P':: BE : B A (i) 
and P' : w: : B D : D E 
Or, substituting in the second analogy the equivalent of the ratio, B D t D E, 
P': w:: rad : cosbdc ( 2 ) 
Wherefore, compounding (1) and (2), and calling rad = 1, 
P : w:: BE : B A* cos B D C (3) 
Now, by trigonometry, B E = B C * sin B C E = B C • sin (B D C C B D) 
=:BC (sinBDC- cos C B D cos B D C • sin C B D). 
Hence, substituting in (3), 
P : W:: B C (sin B D C* cos C B D -1- cos B DC - sin C BD) : B A’ 
cos B D C. 
And dividing by B C’ cos B D C, „ . 
P : W: : (tan B D c- cos C B D + sin C B D) : 
BC 
BA 
Or, P : W :: (tan B D CH- tan C B D) cosC B D 
„ _ _ ® C 1 
Finally, P : W '.t g (tan B D C + tan C B D) cos C B D- • (4) 
We see hence, that P being constant, W varies as a function of the 
C B D, B D C, viz. as, (tan B D C + tan C B dTcos C B D 
angles 
