520 Retrospective Criticism. 



probably been hit on, without consideration of the principle on which it is 

 founded. If this reasoning be correct, it is superior to every other form, and 

 the only improvement it is capable of, is by considering and calculating the 

 proportion of the cone, as it is too much to suppose that the best modifica- 

 tion of it has been hit off at the first heat of the invention or application. I 

 cannot help thinking that Mr. Rogers overrates the eifect of friction in fixing 

 his level, especially when you deduct the weight of the column to be raised 

 perpendicularly to the upper or flowing point. However, it cannot be of very 

 much importance either way. My observation only went to guard against 

 the effects of the somewhat loose manner in which it was treated in his first 

 paper. 



In his courteous answer to my last note, Mr. Rogers has mistaken my mean- 

 ing, which is of itself of little importance j but, as it may be of very grave 

 consequence in bringing his excellent plan into general use, I will endea- 

 vour to correct it. The words of Mr. Rogers are : " With respect to the given 

 quantity of water which any boiler would heat to boiling, a little reflection 

 will, I think, show that it is a question not admitting a definite answer, and 

 that, if answered, could lead to no practical result." I perfectly agree with 

 Mr. Rogers, that such an enquiry would be loss of time, but my meaning was 

 wholly different. So far from wishing to ascertain the quantity of water each 

 boiler would boil, ray object is to ascertain what quantity each would heat to 

 200°, or thereabouts, boiling being expressly guarded against in my view of 

 the case. It is very clear that there must be a limit to the capacity of each- 

 sized boiler ; and, assuming 200° as the best point of comparison, there would 

 be no great difficulty in ascertaining how much each size would manage, when, 

 by measuring the cooling surface of the house, it could be easily put in the 

 power of any amateur or working gardener to estimate the size his house would 

 require. 



This very important point should be attended to either by the inventor or 

 the manufacturer, and the hope of inducing them to do so, and consequently 

 to enhance the value of this simple and excellent invention to the horticultural 

 public, by extending its use, is the sole reason of my recurring to the subject. 



I perfectly agree as to the greater friction of 2-inch pipes ; on which account, 

 as well as their being liable to choke from impurities of water, being more 

 subject to defects in the casting, and the economy which appears to be 

 their sole recommendation being trifling, they should probably be banished 

 from any houses of importance. Of course the friction is very much aug- 

 mented by elbows and turns, especially by descents to cross footways and the 

 like. — W. 



The Black Eagle Cherry. — I see that the Black Eagle Cherry, to which I 

 gave a good character at p. 264., is denounced in strong terras by T. R. of 

 Liverpool, at p. 373. The size of fruits must of course be estimated by com- 

 parison with others of the same class, and according to this rule I judged the 

 cherry in question, making it a good-sized (that is, a middle-sized) fruit, in- 

 termediate between the small kinds, such as the Corone, and the large, like 

 the Bigarreau. ^y referring to the Horticultural Society's Vruit Catalogue, I 

 find my estimate of this cherry confirmed, for it is there classed with the May 

 Duke, Kentish, and others, as a second or middle-sized fruit ; it is, moreover, 

 stated to be of the first quality, and as the account of its quality there given 

 is the result of perhaps as much experience as T. R. can boast, many persons 

 will have the hardihood to consider the author of that work the better autho- 

 rity of the two. I have myself grown the Black Eagle, and therefore am 

 enabled flatly to contradict this libeller of cherries, who says that " a poorer, 

 more vapid fruit was never produced." Either T. R. does not know the 

 Black Eagle, or the inferiority of his fruit is the result of some defect in soil, 

 situation, or management. — J. B. W. Jidy 8. 



