essays-1-第58章
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to little purpose。 And hence it appears of how much importance it is； whether it be considered with a view to economy； or to cleanliness； comfort； and elegance； to pay due attention to the management of a Chimney Fire。
Nothing can be more perfectly void of common sense； and wasteful and slovenly at the same time； than the manner in which Chimney Fires； and particularly where coals are burned； are commonly managed by servants。 They throw on a load of coals at once； through which the flame is hours in making its way； and frequently it is not without much trouble that the fire is prevented from going quite out。 During this time no heat is communicated to the room； and what is still worse； the throat of the Chimney being occupied merely by a heavy dense vapour； not possessed of any considerable degree of heat； and consequently not having much elasticity； the warm air of the room finds less difficulty in forcing its way up the Chimney and escaping； than when the fire burns bright；and it happens not unfrequently； especially in Chimneys and Fire…places ill constructed； that this current of warm air from the room which presses into the Chimney； crossing upon the current of heavy smoke which rises slowly from the fire； obstructs it in its ascent； and beats it back into the room； hence it is that Chimnies so often smoke when too large a quantity of fresh coals is put upon the fire。 So many coals should never be put on the fire at once as to prevent the free passage of the flame between them。 In short； a fire should never be smothered； and when proper attention is paid to the quantity of coals put on； there will be very little use for the poker； and this circumstance will contribute very much to cleanliness； and to the preservation of furniture。
Those who have feeling enough to be made miserable by any thing careless； slovenly； and wasteful which happens under their eyes；who know what comfort is； and consequence are worthy of the enjoyments of a CLEAN HEARTH and a CHEERFUL FIRE； should really either take the trouble themselves to manage their fires； （which； indeed； would rather be an amusement to them than a trouble；） or they should instruct their servants to manage them better。
But to return to the subject more immediately under consideration。 As we have seen what is necessary to the production or generation of radiant heat； it remains to determine how the greatest proportion of that generated and sent off from the fire in all directions may be made to enter the room； and assist in warming it。 How as the rays which are thrown off from burning fuel have this property in common with light； that they generate heat only WHEN and WHERE they are stopped or absorbed； and also in being capable of being reflected WITHOUT GENERATING at the surfaces of various bodies； the knowledge of these properties will enable us to take measures； with the utmost certainty； for producing the effect required；that is to say； for bringing as much radiant heat as possible into the room。
This must be done； first； by causing as many as possible of the rays； as they are sent off from the fire in straight lines； to come DIRECTLY into the room； which can only be effected by bringing the fire as far forward as possible； and leaving the opening of the Fire…place as wide and as high as can be done without inconveniences； and secondly； by making the sides and back of the Fire…place of such form； and constructing them of such materials； as to cause the direct rays from the fire； which strike against them； to be sent into the room BY REFLECTION in the greatest abundance。
Now it will be found； upon examination； that the best form for the vertical sides of a Fire…place； or the COVINGS； （as they are called；） is that of an upright plane； making an angle with the plane of the back of the Fire…place； of about 135 degrees。 According to the present construction of Chimnies this angle is 90 degrees； or forms a right angle； but as in this case the two sides or covings of the Fire…place （AC； BD； Fig。 1。） are parallel to each other； it is evident that they are very ill contrived for throwing into the room by reflection the rays from the fire which fall on them。
To have a clear and perfect idea of the alterations I propose in the forms of Fire…places； the reader need only observe； that； whereas the backs of Fire…places； as they are now commonly constructed； are as wide as the opening of the Fire…place in front； and the sides of it are of course perpendicular to it； and parallel to each other；in the Fire…places I recommend； the back （i k； Fig。 3） is only about one…third of the width of the opening of the Fire…place in front （a；b）； and consequently that the two sides of covings of the Fire…place （a i and b k）； instead of being perpendicular to the back； are inclined to it at an angle of about 135 degrees； and in consequence of this position； instead of being parallel to each other； each of them presents an oblique front towards the opening of the Chimney； by means of which the rays which they reflect are thrown into the room。 A bare inspection of the annexed drawings （Fig。 1。 and Fig。 3。） will render this matter perfectly clear and intelligible。
In regard to the materials which it will be most advantageous to employ in the construction of Fire…places； so much light has； I flatter myself； already been thrown on the subject we are investigating； and the principles adopted have been established on such clear and obvious facts； that no great difficulty will attend the determination of that point。As the object in view is to bring radiant heat into the room； it is clear that that material is best for the construction of a Fire…place which reflects the most； or which ABSORBS THE LEAST of it； for that heat which is ABSORBED cannot be REFLECTEDNow as bodies which absorb radiant heat are necessarily heated in consequence of that absorption； to discover which of the various materials that can be employed for constructing Fire…places are best adapted for that purpose； we have only to find out by an experiment； very easy to be made； what bodies acquire LEAST HEAT when exposed to the direct rays of a clear fire；for those which are least heated； evidently absorb the least； and consequently reflect the most radiant heat。 And hence it appears that iron； and； in general； metals of all kinds； which are well known to GROW VERY HOT when exposed to the rays projected by burning fuel； are to be reckoned among the VERY WORST materials that it is possible to employ in the construction of Fire…places。
The best materials I have hitherto been able to discover are fire…stone； and common bricks and mortar。 Both these materials are； fortunately； very cheap； and as to their comparative merits； I hardly know to which of them the preference ought to be given。
When bricks are used they should be covered with a thin coating of plaster； which； when it is become perfectly dry； should be white…washed。 The fire…stone should likewise be white washed； when that is used； and every part of the Fire…place； which is not exposed to being soiled and made black by the smoke； should be kept as white and clean as possible。 As WHITE reflects more heat； as well as more light than any other colour； it ought always to be preferred for the inside of a Chimney Fire…place； and BLACK； which reflects neither light nor heat should be most avoided。
I am well aware how much the opinion I have have ventured to give； respecting the unfitness of iron and other metals to be employed in the construction of open Fire…places； differs from the opinion generally received upon that subject；and I even know that the very reason which； according to my ideas of the matter； renders them totally unfit for the purpose； is commonly assigned for making use of them； namely； that they soon grow very hot。 But I would beg leave to ask what advantage is derived from heating them？
I have shown the disadvantage of it； namely； that the quantity of radiant heat thrown into the room is diminished；and it is easy to show that almost the whole of that absorbed by the metal is ultimately carried up the Chimney by the air； which； coming into contact with this hot metal； is heated and rarefied by it； and forcing its way upwards； goes off with the smok
