PINE-APPLE——BOTTOM HEAT. 349 
more convenient, and afford a heat sufficient both in in- 
tensity and duration for any useful purpose. 
We have already shown how a system of tubes trans- 
tmitting steam or hot water may be made available for the 
Fig. 46. 
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production of bottom-heat. There is another method wor- 
thy of at least a cursory notice. Its invention is due to 
