Of Chimney Fireplaces. 533 



show these various alterations in a clear and satisfactory 

 manner. In this figure, as well as in most of the others 

 in this essay, the old walls are distinguished from the 

 new ones by the manner in which they are shaded; the 

 old walls being shaded by diagonal lines, and the new 

 ones by vertical lines. The additions, which are formed 

 of plaster, are shaded by dots instead of lines. 



Where the too great height of the breast of a chimney 

 is occasioned, not by the height of the mantle, but by 

 the too great width of the breast, in that case (which, 

 however, will seldom be found to occur), this defect 

 may be remedied by covering the lower part of the 

 breast with a thick coating of plaster, supported, if 

 necessary, by nails or studs driven into the wall which 

 forms the breast, and properly rounded off at the lower 

 part of the mantle. (See Fig. 14.) 



CHAPTER III. 



Of the Cause of the Ascent of Smoke. Illustration of the 

 Subject by familiar Comparisons and Experiments. Of 

 Chimneys which affect and cause each other to smoke. Of 

 Chimneys which smoke from Want of Air. Of the Eddies 

 of Wind which sometimes blow down Chimneys^ and cause 

 them to smoke. 



T 



HOUGH it was my wish to avoid all abstruse 

 _ philosophical investigations in this essay, yet I 

 feel that it is necessary to say a few words upon a sub- 

 ject generally considered as difficult to be explained, 

 which is too intimately connected with the matter under 



