A>'D CONSERVATORY. 41 



matter to go deep enough for the furnace. This ease affords 

 an example of heating on the level, and must be described with 

 some detail. The houses to be heated are a lean-to and a 

 Paxtonian ; they are so nearly on a level that a quick circula- 

 tion is not to be hoped for, and the lean-to has beside it a well, 

 which frequently overflows in the winter season. Between 

 the highest point the water reaches and the flow-pipe in the 

 lower house the perpendicular difference is thirty inches, and 

 between the bottom of the boiler and the level of the water 

 the difference is only fifteen inches. 



If you want the quickest possible circulation of hot water, 

 fit a perpendicular syphon through a saucepan lid, seal the lid 

 down waterproof and fireproof, insert a small tube at the top 

 of tlie syphon, and through that tube fill the whole concern 

 with water, and then put the saucepan on the fire. The cir- 

 culation will begin instanter, and will be perfect from the first 

 moment that accessions of heat are communicated from the 

 fire to the water. The laws which regulate the movements of 

 heated fluids are fully explained and illustrated in the books 

 that treat of physics and natural philosophy, so it is not worth 

 while to go into that part of that subject here. It only con- 

 cerns us to know that in a perpendicular column of water the 

 movements caused by heat are most decisive and complete, 

 and that every deviation fi*om the perpendicular tends to arrest 

 the motion, so that when we reach the horizontal, the rate of 

 motion is reduced to a minimum, or may absolutely cease 

 altogether, which in a certain sense is less than a minimum, as 

 nothing is less than the least. In the heating of these two 

 houses we had to calculate to a great nicety how to make the 

 most of the perpendicular space at command — to consider, in 

 fact, how much could be done between the lowest point at 

 which the pipes could be placed in the houses, and the highest 

 level of the water in the well. The lower house was the only 

 difiiculty ; the other was so far above it that if we ever got a 

 fire to burn, and water to get hot thereby, on a level suffi- 

 ciently low to heat the lower house, the Paxtonian would be 

 safe enough. 



Now, it is worthy of observation that the plan adopted in 

 this case was not the only one at our command. We might 

 have taken round the houses Vi flow-pipe of very small lore and 

 a return-pipe of very large hove, and by this means have 

 secured a circulation, and derived our heat from the returu- 



