1879.] HEATING BY HOT WATER. 471 



at the temperature of 98° in a 4-inch pipe 4 feet high is approximately 

 equal to 344.72063918 ounces avoirdupois, and that of the return is 

 equal to 348.17828489 oz. The difference between the pressures is 

 3.45764571 oz. Now suppose we raise the elevation to 8 feet, the 

 pressure of the flow is increased to 689.44127836 oz., and that of the 

 return to 696.35656978 oz. The difference of pressure is 6.91529142. 

 Hence we see that the difference of pressure at 8 feet is double that at 

 4 feet. But with the same source of heat, circulation would not be 

 doubled, as it is plain that the difference between the mean temperatures 

 of the two volumes becomes less as the rapidity of circulation increases. 

 Thus we see that the rapidity of circulation increases in proportion to 

 the difference of pressure on the base, and that the difference of pres- 

 sure is increased by elevation. I will not trespass further on your 

 valuable space; but I may say, in conclusion, that though what has been 

 said may not convince Mr Hammond that he is in error, it may help 

 to convince some of your intelligent readers who may have any doubts 

 on the subject. C. M. 



I received a few days ago a copy of the August number of ' The 

 Gardener,' and was so interested in the articles it contained on heat- 

 ing by hot water, that I at once procured all the earlier numbers 

 having reference to the subject. Allow me at once to say that I agree 

 with most of the views so clearly expressed by Mr Makenzie, and 

 most especially with that as to the obligation we hot-water engineers 

 should be under to Mr Hammond, if he is able to show us a method 

 by which three or more houses can be heated from one boiler without 

 a deep stoke-hole. I presume I am right in confining the discussion 

 within these limits, as it is, I believe, admitted by all engineers that 

 where only one, and occasionally two houses, have to be heated, it is 

 easy to obtain a satisfactory result with the boiler level with, or even 

 above, the pipes. I shall be glad to supplement Mr Makenzie's list 

 of heating apparatus so erected during the last fifteen years. 



Mr Hammond wishes, in his last, to confine the discussion to two 

 points. Respecting the first, he gives some reasons why he says no ; 

 but I fail to see an explanation in any of his letters as to how more 

 than two compartments or houses can be heated as he proposes, with 

 bottom of boiler only 1 foot below the pipes. He admits that outside 

 paths cannot be crossed, but is silent as to inside paths. Will he 

 kindly answer Mr Makenzie's question, p. 231, as to inside paths 1 



Glass houses are, or should be, arranged so that plants may be 

 grown successfully, with the greatest economy of labour possible, not 

 to put hot-water apparatus in ; and a system which will not admit of 

 doors and paths being placed where required is at once condemned, 

 even if the water does circulate the best in that form. Then, again, 

 with a continuous fall from boiler, the placing of pipes under stages 



