essays-1-第51节
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tself； we must consider them all together。
That these inquiries may be pursued with due method； and that the conclusions drawn from them may be clear and satisfactory； it will be necessary to consider； first； what the objects are which ought principally to be had in view in the construction of a Fire…place； and secondly； to see how these objects can best be attained。
Now the design of a Chimney Fire being simply to warm a room； it is necessary； first of all； to contrive matters so that the room shall be actually warmed； secondly； that it be warmed with the smallest expence of fuel possible； and； thirdly； that in warming it； the air of the room be preserved perfectly pure； and fit for respiration； and free from smoke and all disagreeable smells。
In order to take measures with certainty for warming a room by means of an open Chimney Fire； it will be necessary to consider HOW； or in WHAT MANNER； such a Fire communicates heat to a room。 This question may perhaps； at the first view of it； appear to be superfluous and trifling； but a more careful examination of the matter will show it to be highly deserving of the most attentive investigation。
To determine in what manner a room is heated by an open Chimney Fire； it will be necessary first of all to find out； UNDER WHAT FORM the heat generated in the combustion of the fuel exists； and then to see how it is communicated to those bodies which are heated by it。
In regard to the first of these subjects of inquiry； it is quite certain that the heat which is generated in the combustion of the fuel exists under TWO perfectly distinct and very different forms。 One part of it is COMBINED with the smoke； vapour； and heated air which rise from the burning fuel； and goes off with them into the upper regions of the atmosphere； while the other part； which appears to be UNCOMBINED； or； as some ingenious philosophers have supposed； combined only with light； is sent off from the fire in rays in all possible directions。
With respect to the second subject of inquiry； namely； how this heat； existing under these two different forms； is communicated to other bodies； it is highly probable that the combined heat can only be communicated to other bodies by ACTUAL CONTACT with the body with which it is combined； and with regard to the rays which are sent off by burning fuel； it is certain that THEY communicate or generate heat only WHEN and WHERE they are stopped or absorbed。 In passing through air； which is transparent； they certainly do not communicate any heat to it； and it seems highly probable that they do not communicate heat to solid bodies by which they are reflected。
In these respects they seem to bear a great resemblance to the solar rays。 But in order not to distract the attention of my reader； or carry him too far away from the subject more immediately under consideration； I must not enter too deeply into these inquiries respecting the nature and properties of what has been called RADIANT HEAT。 It is certainly a most curious subject of philosophical investigation； but more time would be required to do it justice than we now have to spare。 We must therefore content ourselves with such a partial examination of it as will be sufficient for our present purpose。
A question which naturally presents itself here is。 What proportion does the radiant heat bear to the combined heat？Though that point has not yet been determined with any considerable degree of precision； it is； however； quite certain； that the quantity of heat which goes off combined with the smoke； vapour； and heated air is much more considerable； perhaps three of four times greater at least； than that which is sent off from the fire in rays。And yet； small as the quantity is of this radiant heat； it is the only part of the heat generated in the combustion of fuel burnt in an open Fire…place which is ever employed； or which can ever be employed； in heating a room。
The whole of the combined heat escapes by the Chimney； and is totally lost； and； indeed； no part of it could ever be brought into a room from an open Fire…place； without bringing along with it the smoke with which it is combined； which； of course； would render it impossible for the room to be inhabited。 There is； however； one method by which combining heat； and even that which arises from an open Fire…place； may be made to assist in warming a room； and that is by making it pass through something analogous to a German stove； placed in the Chimney above the fire。But of this contrivance I shall take occasion to treat more fully hereafter； in the mean time I shall continue to investigate the properties of open Chimney Fire…places； constructed upon the most simple principles； such as are now in common use； and shall endeavour to point out and explain all those improvements of which THEY appear to me to be capable。 When fuel is burnt in Fire…places upon this simple construction； where the smoke escapes immediately by the open canal of the Chimney； it is quite evident that all the combined heat must of necessity be lost； and as it is the radiant heat alone which can be employed in heating a room； it becomes an object of much importance to determine how the greatest quantity of it may be generated in the combustion of the fuel； and how the greatest proportion possible of that generated may be brought into the room。
Now the quantity of radiant heat generated in the combustion of a given quantity of any kind of fuel depends very much upon the management of the fire； or upon the manner in which the fuel is consumed。 When the fire burns bright； much radiant heat will be sent off from it； but when it is SMOTHERED UP； very little will be generated； and indeed very little combined heat； that can be employed to any useful purpose： most of the heat produced will be immediately EXPENDED in giving elasticity to a thick dense vapour or smoke which will be seen rising from the fire； and the combustion being very incomplete； a great part of the inflammable matter of the fuel being merely rarefied and driven up the Chimney without being inflamed； the fuel will be wasted 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 r
