SOME REMARKS ON HEATING. 295 



When a large crop of white clover makes its appearance on lands 

 recovered from the sea, it is an easy solution of the difficulty to 

 say that the plants have been generated spontaneously from the 

 soil. It may not be easy to account for their presence, but yet 

 the lover of truth will not readily solve the difficulty by such an 

 unwarranted conclusion. In the case of the potato disease and 

 of tlie grape mildew it appears pretty clear that the parasites 

 were not previously known. Tiie conclusion is then, as Morren 

 well remarked respecting the former, that they must have been 

 imported, and there is no more difficulty in this notion, nor 

 indeed so niucli, as that of the introduction of such a quantity of 

 white clover seed into the tracts recovered from the sea. In 

 every branch of natural history ttiere are difficulties enougli, and 

 it would be surprising indeed if there were none wliere such 

 minute productions are concerned. The reflective mind will 

 often observe with combined wonder and admiration how the 

 Almighty produces effects of great magnitude and importance, 

 which are at the first view altogether incommensurate with the 

 causes from wlience they are derived. 



XXIX. — Some Remarks on Heating. By Robert Glendinning, 

 F.H.S., Chiswick Nursery, Turnham Green. 

 (Communicated September 22, 1851.) 

 It appears to me tliat no system of warming liorticultural build- 

 ings hitherto devised has been found so effectual as liot water 

 applied by a properly contrived apparatus. Even although so 

 many are interested in the subject, during the last twenty-five 

 years little advance has been made in the metliods of heating. If 

 the law which governs the circulation of water in pipes, then 

 and now in use, was not so clearly understood, it was at least as 

 efficiently applied. It is true that a vast number of contrivances 

 has been submitted to the public, all more or less setting physical 

 science at defiance, and therefore proving either inefficient in 

 power, or total failures. The object aimed at in these contri- 

 vances has apparently been to involve the simplicity of ordinary 

 hot water systems by complex mechanical appliances ; so far 

 indeed has this tlurst for complexity been carried, that the ex- 

 pense attending the setting up of these unphilosophical inven- 

 tions has in many cases been doubled. Now, in the warming of 

 the great proportion of horticultural buildings, the most simple 

 form of apparatus can be readily applied, and almost always to 

 more advantage, and at a considerably reduced outlay. Every 

 deviation from this, whether from caprice or necessity, either 

 decreases the heating power, or increases the price. 



