160 HEATING AS APPLIED IN HORTICULTURE. 



the flue, and is thus defended from the 

 radiant heat of the fuel on all sides but 

 one : this heating-pipe is continued from 

 the upper part of the fire-chamber into 

 the building ; z is the return-pipe which 

 enters the lower part of the furnace, and 

 passes through the bearing bars of the 

 fire grating to prevent their overheating." 



The want of an equal diffusion of heat 

 in these pipes arises from the friction 

 and number of bendings, and hence the 

 same quantity of fuel expended in the 

 furnace will not heat the same amount of 

 air as it would do were the temperature 

 more uniform in them. In regard to the 

 quantity of pipe used in the furnace coil, 

 it appears from pretty correct data that 

 it should amount to from a seventh to a 

 fourth of the whole extent of heating-pipe 

 employed ; and although by this system 

 the pipes become much sooner heated 

 than by any other, it does not follow that 

 the room or hothouse to which it is 

 attached will be warmed sooner than by 

 a well-appointed hot-water apparatus of 

 more simple construction. 



" This great rapidity of heating is, how- 

 ever, no advantage in many situations. 

 The apparatus being as quickly cooled as 

 it is heated, and its general temperature 

 rapidly fluctuating at every variation of 

 the combustion in the furnace, in all 

 places where permanency and uniformity 

 of temperature are essential, the low- 

 pressure apparatus, in which a great body 

 of water acts as a regulator as well as a 

 reservoir of heat, is to be preferred • and 

 it is obvious that the same quantity of 

 heating surface, at the same temperature, 

 in every variety of warming apparatus, 

 heats the same quantity of air. From 

 the comparatively small surface of pipe 

 exposed to the radiant heat of the fur- 

 nace, and the high temperature at which 

 the smoke escapes from it, the coiled-pipe 

 boiler has been thought much less eco- 

 nomical of fuel than the low-pressure 

 boiler. It is not found to be so in prac- 

 tice. All circumstances being similar, 

 the high-pressure coil requires about the 

 same quantity of fuel that is necessary 

 for a common boiler." — Bernan in Hist, 

 of Heating, fyc. 



The mode of connecting Perkins' hot- 

 water pipes is both ingenious and secure. 

 They are of wrought-iron, and are I of 

 an inch thick ; the iron of which they 



are made, being rolled out into sheets of 

 the requisite width and thickness, is then 

 brought close at the edges and welded 

 together. They are in general 12 feet in 

 length, and are screwed at each end, and 

 proved, by hydraulic power, to resist an 

 internal pressure of 3000 lb. to the square 

 inch ; and from the ductility and purity 

 of the metal, they are easily bent, when 

 cold, into coils of different sizes and shapes. 

 Mr Richardson, in a very interesting 

 work on warming and ventilation — evi- 

 dently written in support of this mode 

 of heating— thus describes the mode of 

 joining the pipes : "When two tubes are 

 to be joined, the ends are placed within a 

 socket , forming a right and left hand- 

 screw, the edge of one tube being flat- 

 tened and the other sharpened ; they are 

 then screwed so tight, that the sharpened 

 edge of one pipe is indented in the flat- 

 tened surface of the other. The great 

 advantage of these joints is, that they can 

 be taken to pieces in the event of altera- 

 tions being required, which is in all other 

 cases a very different affair." 



Eckstein andBushbfs method— tig. 173. — 

 The merits of this invention are, that mo- 

 tion is given 

 by means of a 

 fly built in the 

 chimney, and 

 turned by the 

 smoke of the 

 boiler flue. It 

 is a happy 

 application of 

 dynam ical 

 principles to 

 overcome one of the most constant of 

 nature's laws by the development of an 

 antagonist force. The plan has, however, 

 seldom been adopted, although it is ca- 

 pable of being applied in cases otherwise 

 difficult, and which cannot, by the more* 

 simple apparatus, be effected. A pecu- 

 liar singularity in this invention is, that 

 the boiler may be placed in a garret, and 

 the hot water forced downwards. The 

 boiler, which may be either open or 

 closed, has a pipe a fixed to its circum- 

 ference, which may be carried in any direc- 

 tion, either upwards, downwards, or hori- 

 zontally, but finally must return exactly 

 to the centre of the boiler at b. The float 

 c is fixed on centres, and revolves freely 

 in the boiler. The rapid rotation of the 



