he puts it again into its place. -- The annexed drawing (No. 6.) will give a clear idea of this contrivance; and the experience I have had of it has proved that it answers perfectly well the purpose for which it is designed.

I observed above, that the new back, which it will always be found necessary to build in order to bring the fire sufficiently forward, in altering a Chimney constructed on the common principles, need never be thicker than the width of a common brick. -- I may say the same of the thickness necessary to be given to the new sides, or covings, of the Chimney; or if the new back and covings are constructed of stone, one inch and three quarters, or two inches in thickness will be sufficient. -- Care should be taken in building up these new walls to unite the back to the covings in a solid manner.

Whether the new back and covings are constructed of stone, or built of bricks, the space between them, and the old back and covings of the Chimney ought to be filled up, to give greater solidity to the structure. -- This may be done with loose rubbish, or pieces of broken bricks, or stones provided the work be strengthened by a few layers or courses of bricks laid in mortar; but it will be indispensably necessary to finish the work, where these new walls end, that is to say, at the top of the throat of the Chimney, where it ends abruptly in the open canal of the Chimney by a horizontal course of bricks well secured with mortar. -- This course of bricks will be upon a level with the top of the door-way left for the Chimney-sweeper.

From these descriptions it is clear that where the throat of the Chimney has an end, that is to say, where it enters into the lower part of the open canal of the Chimney, there the three walls which form the two covings and the back of the Fire-place all end abruptly. -- It is of much importance that they should end in this manner; for were they to be sloped outward and raised in such a manner as to swell out the upper extremity of the throat of the Chimney in the form of a trumpet, and increase it by degrees to the size of the canal of the Chimney, this manner of uniting the lower extremity of the canal of the Chimney with the throat would tend to assist the winds which may attempt to blow down the Chimney, in forcing their way through the throat, and throwing the smoke backward into the room; but when the throat of the Chimney ends abruptly, and the ends of the new walls form a flat horizontal surface, it will be much more difficult for any wind from above, to find, and force its way through the narrow passage of the throat of the Chimney.

As the two walls which form the new covings of the Chimney are not parallel to each other; but inclined, presenting an oblique surface towards the front of the Chimney, and as they are built perfectly upright and quite flat, from the hearth to the top of the throat, where they end, it is evident that an horizontal section of the throat will not be an oblong square; but its deviation from that form is a matter of no consequence; and no attempts should ever be made, by twisting the covings above, where they approach the breast of the Chimney, to bring it to that form. -- All twists, bends, prominences, excavations, and other irregularities of form, in the covings of a Chimney, never fail to produce eddies in the current of air which is continually passing into, and through an open Fire-place in which a fire is burning; -- and all such eddies disturb, either the fire, or the ascending currents of smoke, or both; and not unfrequently cause the smoke to be thrown back into the room. -- Hence it appears, that the covings of Chimneys should never be made circular, or in the form of any other curve; but always quite flat.

For the same reason, that is to say, to prevent eddies, the breast of the Chimney, which forms that side of the throat that is in front, or nearest to the room, should be nearly cleaned off, and its surface made quite regular and smooth.

This may easily be done by covering it with a coat of plaster, which may be made thicker or thinner in different parts as may be necessary in order to bring the breast of the Chimney to be of the proper form.

With regard to the form of the breast of a Chimney, this is a matter of very great importance, and which ought always to be particularly attended to. -- The worst form it can have is that of a vertical plane, or upright flat; -- and next to this the worst form is an inclined plane. -- Both these forms cause the current of warm air from the room, which will, in spite of every precaution, sometimes find its way into the Chimney, to cross upon the current of smoke, which rises from the fire, in a manner most likely to embarrass it in its ascent, and drive it back. -- The inclined plane which is formed by a flat register placed in the