The tar vessel or vessels, as the case may be, are lodged in the space between and upon the boilers, and a small fire may be made under them, if necessary. A pipe leads steam in at one end, two pipes at the other; one near the bottom, and one near the top, lead out the tar and steam. These pipes unite below; the steam and tar, thus mingled in suitable proportions, flow to the main fire, or the flues of the boilers, as well as to the coal-fire below, where the gas and tar are ignited. The fireman judges of the proportion of each, by the effect; the object being to produce a nearly white flame without appearance of tar. Thus flame is applied to the greatest possible surface, and the apparatus adds very little to the cost of the engine. There are also two improvements in the boiler, which I deem it important to mention. First, the lining or covering of the flue within with sheet-iron or copper, _perforated with small holes_, reaching down its sides, nearly to the bottom. Plate III. Fig. 2. _a_ the boiler; _b_ the flue; _d_ the grate; _c c_ the lining. This causes the water to circulate rapidly between them to the top of the flue, and protects it from being run dry, or heated red hot, when the water gets, by accident, too low. The lining also _causes the steam to form much faster, in consequence of this circulation_. The other is the interior boiler. A vessel occupying the back part of the flue. Plate II. Fig. 8. (_d_) communicating downwards with the water, and upwards with the steam of the main boiler. The fire acts upon it very forcibly, surrounding it on all sides. I have said there is no reciprocating movement in Morey's engine. Should it be objected that the piston moves in the cylinder as usual, it must be apparent that it also moves circularly; it is in fact the cylinder that moves, carrying the piston with it, which gives and keeps up the motion, by drawing and pressing on the centre-piece, and communicating the resistance thence to the _guides_ of the cross-piece on the insides of the frame, which thus receives its motion. In fact, this form of the engine seems divested of all the usual drawbacks on its power, and leaves it to act freely with any velocity, according to the strength of the steam in the boilers. Such it appears in principle, and such thus far in practise. I have therefore preferred it for the purposes of navigation, and have purchased the patent right. But, though interested to recommend it, I cannot expect it to be preferred by the intelligent, if there is not merit in the invention, and great economy in its use. It may be considered the most direct application of the power, and the most unexceptionable mode of using the expansive force of high steam. And from the nature of its movement the most applicable to boats and vessels.