322 Retrospective Criticism. 



fins, Architect, 1, Lees Street, Piccadilly, Manchester. 21. R. H. Essex, 

 13. York Buildings, New Iload. 



The Competilion Desigiis for the Botanic Society's Garden in the Inner Circle, 

 Regent's Park, were opened for public exhibition on April the 8th. They 

 are 20 in number, and almost all by arcliitects. We have glanced over them 

 once, and shall probably have to speak of them more in detail on some future 

 occasion. In the meantime we cannot help expressing a feeling of some- 

 thing more than disappointment on seeing so many designs, and yet not one 

 among them that, even with considerable alterations, would, in our opinion, 

 be fit to be executed. We could name a score of gentlemen's gardeners, any 

 one of whom would produce a better plan than the best in this exhibition. 

 It is singular that in a country celebrated for its landscape-gardening and its 

 horticulture, such a number of designs should have been produced of so little 

 merit. — Coiul. 



The above was written on returning from the exhibition on the day when it 

 was opened. We have since examined the plans twice, at the request of the 

 Council, in order to aid them in deciding to which plan the prize ought to be 

 awarded, and we see no reason to alter the opinion first formed. There is not 

 one of the plans, as we think, fit to be executed, even with considerable al- 

 terations, supposing the Society to be rich enough to do so. All that the 

 Council can do, therefore, is to determine which of the competitors has best 

 complied with the conditions laid down in their "Instructions." The pre- 

 mium, fifty guineas, has not yet been awarded. 



Art. VII. Retrospective Criticism. 



The Advantage of placing Hot-water Pipes higher than the Boiler, (p. 227.) 

 — Your intelligent correspondent, W. of Darlington, deserves my thanks for his 

 clear explanation of the mistake into which Mr. Beaton had fallen on the sub- 

 ject of conical boilers ; and the least acknowledgement I can make him is to 

 answer his own questions as far as I can. 



He wishes to know what is the advantage of placing " the pipes much 

 higher than the boiler ; and considers 1 ft., my minimum, as quite sufficient." 

 Under ordinary circumstances, and perhaps always with 4-inch pipe, it is suf- 

 ficient ; but where smaller pipe is employed, it may be desirable to have the 

 pipes considerably higher above the boiler. The moving force, and, conse- 

 quently, the velocity of circulation, depend upon the difference in weight be- 

 tween the ascending and descending column : now, the greater the height of 

 these columns, the greater the difference in their weight ; and, consequently, 

 the greater the velocity of circulation, and the higher the mean temperature of 

 the pipes. With 4-inch pipe this is unimportant, for the volume of water con- 

 tained in them is large as compared with their radiating surface ; so that, with 

 any given velocity, the water loses less heat in one circulation than it would in 

 smaller pipes. Moreover, in 4~inch pipes the friction is small, and offers Httle 

 resistance to circulation, so that in 4-inch pipe there is little need of very 

 rapid circulation, and little resistance to such circulation : but with smaller 

 pipe there is need of more rapid motion, or the water in the return pipe will 

 be much colder than in the delivery pipe : to take the instance of 2-inch 

 pipe, and suppose the circuit of equal length and the velocity equal in both 

 cases, the difference of temperature between the flow and return pipes will be 

 four times as great as it would with 4-inch pipe, because the volume of water 

 conveying heat is only one fourth of that contained in the larger pipes. It is 

 true this difference of temperature increases the difference of weight in the 

 column, i. e. the moving force, and the supposition of equal velocities does not 

 hold good in practice ; but with increased velocity comes increased friction ; 

 and, moreover, with diminished diameter comes increased friction also ; so 

 that, with the boiler of the same height, it is impossible to heat a given length 

 of 2-inch pipe to the same mean temperature with an equal length of 4-inch. 



