and the Mode of its Communication. 179 
for warming rooms, or for heating drying-rooms, the external 
surface of those tubes should be painted, or covered with some 
substance which facilitates the emission of calorific rays. A 
covering of thin paper will answer that purpose very well, espe- 
cially if it be black, and if it be closely and firmly attached to 
the surface of the metal with glue. 
Tubes which are designed for conveying hot steam from one 
place to another, should either be well covered up with warm 
covering, or should be kept clean and bright. It would, I am 
persuaded, be worth while, in many cases, to gild them, or at 
least to cover them with what is called gilt paper, or with tin 
foil, or some other metallic substance which does not easily 
tarnish in the air. 
The cylinders, and principal steam-tubes of steam-engines, 
might be covered, first with some warm clothing, and then with 
thin sheet brass, kept clean and bright. The expence of this 
covering would, I am confident, be amply repaid, by the saving 
of heat and fuel which would result from it. 
If garden walls painted black acquire heat faster, when exposed 
to the sun’s direct rays, than when they are not so painted, they 
will likewise cool faster, during the night ; and gardeners must 
be best able to determine whether these rapid changes of tem- 
perature are, or are not, favourable to fruit trees. 
Black clothes are well known to be very warm in the sun ; 
but they are far from being so in the shade, and especially in 
cold weather. No coloured clothing is so cold as black, when 
the temperature of the air is below that of the surface of the 
skin, and when the body is not exposed to the action of calorific 
rays from other substances. 
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