i379-] HOT-WATER CIRCULATION. 271 



HOT -WATER CIRCULATION. 



It is not likely that anything new can be added to what is already known 

 on the subject of hot-water circulation — the whole matter has again 

 been made plain by your correspondent, Mr J. Inglis. The heat from 

 the fire rarefying the water, disturbs its equilibrium, and the warmed 

 particles through their buoyancy, like a cork, are forced to ascend, and 

 the cold water, from its greater density, descends to fill its place. It is 

 quite easy to see, however, that your able correspondent, Mr Hammond, 

 is right so far. For a time a counter-current must be produced in the 

 same pipe, the heated water flowing along the upper curve of the pipe, 

 and the cold returning along the under side, like water in the eave- 

 gutter. One's hand placed first on the upper surface and then on the 

 under side of the pipe, will at once prove the truth of this ; and this 

 fact may appear to retard the circulation for a short time, supposing a 

 fire just lighted under a cold boiler. This appears to be all Mr Ham- 

 mond contends for, although his facts may not quite justify his conclu- 

 sions. The illustration of the siphon is used to explain the movement 

 of the water, and though it does not explain all, it is true as far as it 

 goes : the balance of weight in favour of the cold water running down a 

 perpendicular pipe or an inclined plane must accelerate the circulation, 

 if it does not originate it. A very curious instance of the effect of the 

 cold water in deciding the course of the circulation once took place 

 in our experience. It was in this wise : a boiler with three distinct 

 sets of pipes attached was just out of the hands of the mechanics, 

 and all concerned were impatient to see the apparatus tested. One 

 set of pipes was all but on a level with the boiler, another set was 

 some 5 feet and the third set was 10 feet above the boiler. Each 

 set was laid nearly level, but with a perpendicular dip where attached 

 to the boiler. It is with the 10-feet set we have to record our ex- 

 perience more particularly. A good fire was first made to heat 

 the flues and dry the boiler outside, then water was slowly poured 

 into the apparatus down the flow-pipe of the 10-feet set, when very 

 soon the warm water was circulating in the lowest set of pipes, but 

 as the filling proceeded, these again grew cold, and the middle set 

 became warm. The filling went on as described down the flow-pipe 

 of the upper set into the boiler, when the warm water gradually rose 

 up the return pipe, flowed round, and finally arrived by that route 

 into the flow, where the cold water was being run off at a small expan- 

 sion-box over the boiler. The filling finished, to our temporary aston- 

 ishment the circulation continued the reverse way, the warm water 

 rising in the return pipe and returning to the boiler down the flow- 

 pipe. This was to all appearance reversing the order of nature. We 

 have somewhere read that the laws of nature are the same all the world 

 over, except in Ireland ; but the above incident took place in England, 

 where the laws of mechanics and those relating to liquids work har- 



