TRUNK ENGINE. 347
the driving link, as would be the case if the mechanism were that of a steam-engine. Were it used as a pump the formula would be (CJ P-^r. The expression ( F") = c, d is added to show that the piston F"+ and the chamber V~, that is the pair (F), are formed by the links c and d respectively, the block and slider of the turning slider-crank. The principal formula, along with this additional expression for the chambering, is also subjoined in the same way to all the following figures.
Plate XIV. 2 shows a form of steam-engine used by Broderip (1828) and Humphreys (1835)* but specially connected, as the Trunk engine, with the name of Penn. The upper part of the prism c is made into a trunk sufficiently large to allow the pin 3 to fall within instead of beyond it (3 thus lying within 4), and is so formed that the coupler & can swing freely although the axis of 3 be placed far back as in the figure. The trunk greatly diminishes the capacity of the upper part of the chamber, but in this it differs only in degree from the former arrangement, where the piston rod also diminished the capacity of the upper chamber in precisely the same way.
Fig. 3, Plate XIV., is an arrangement designed by Hastief for a steam-engine. It is single-acting only, and the chamber is extended completely over the crank. The piston is made very heavy in order that its weight may to some extent equalize the working of the machine. Hicks has more recently tried to introduce the same arrangement with the frame d placed horizontally ; his engine at the Paris Exhibition attracted more attention than it deserved.^ In order to equalize its action and to carry it over the dead points he used four mechanisms, or rather two pairs of mechanisms with chain- closure as in 46, and worked the valve-gear of one pair from the pistons of the other.
- I have in every case done my best to ascertain the name of the inventor or
first introducer of each machine, but further than this I cannot answer for the priority of those named, or for the dates given. I have had to content myself with infor- mation at second or third-hand in cases where no more direct sources of information have been accessible to me. I therefore make no pretension to give here an historical account of rotary engines or pumps. R.
t Johnson, Imperial Cyclopaedia, Steam-engine, p. Ix. ; also Bernoulli, Dampf- maschinen-lehrc, 1854, p. 321.
Offiziellen bster. Ausstelltingsbericht, 1868, Motoren und Maschinen der allgem. Mechanik, p. 118. etc. Kittoe and Brotherhood's "Paragon" steam-pump is also an example of this mechanism.
Brotherhood's " three cylinder " engine, the general construction of which is
