Retrospective Criticism. 323 



But there is yet another disadvantage to be taken into account on the score 

 of the 2-inch pipe, which is this ; that, as a given boiler is calculated to supply, 

 say 100 ft. of radiating surface, if this 100 ft. of surface is exhibited in the 

 form of 200 ft. of 2-inch pipe, instead of 100 ft. of 4-inch, you have not only 

 the increased friction due to the diminished bore to contend with, but also the 

 increased friction due to a doubled length of pipe ; so that, in order to bring 

 the radiating surface of 200 ft. of 2-inch pipe to the same mean temperature as 

 100 ft. of 4-inch, you require a great increase of moving power, i. e. a great 

 elevation of the pipes above the boiler. 



All, however, that I meant to say, was, that wherever such arrangement was 

 practicable, or as far as it was not inconvenient, the whole of the pipes should 

 be placed above the boiler ; 1 ft. is sufficient, and would be sufficient in all or- 

 dinary cases, even with 2-inch pipe, but the higher the better ; for the higher 

 the pipes are above the boiler, ccBteris paribus, the greater will be the economy 

 of fuel, inasmuch as the heat will be carried ofi^ more rapidly from the boiler. 

 It is a possible condition that small pipes might be properly placed and per- 

 fectly free from air or other impediment, and yet that the water in J;he boiler 

 should boil to waste in steam, although the mean temperature of the pipes fell 

 far short of 200° ; simply because, in a very long length of pipe, if it be laid 

 level with, or only just above, the top of the boiler, the moving force would 

 not be sufficient to overcome the friction. I do not mean to say that this was 

 Mr. Beaton's case, it is highly improbable that it was ; but still it is a possible 

 case if the pipe be not high enough above the boiler ; and such defect may be 

 continually seen, even with 5-inch pipe, in the earlier hot-water apparatus, the 

 boilers of which were extremely shallow. The foregoing explanation will, I 

 trust, be intelligible ; if it be not intelligible, I must request your correspond- 

 ent to refer to Mr. C. Hood's work, where he will find data which establish 

 my statements. With respect to his suggestion that the form of a limekiln 

 (I presume, an inverted cone) would be advantageous, I do not exactly see 

 how it would operate advantageously ; and I fear that the fire would be 

 speedily choked up with ashes and clinkers so as to go out, or that it would 

 be extinguished at bottom by the rapid radiation of heat from a small body of 

 fuel into the water, and continue burning only at the top. "With respect to 

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

 reflection will, I think, show, in the first place, that it is a question not admitting 

 a definite answer, and that, if answered, it could lead to no practical result. * 

 A iew observations on the subject of steaming houses will be found in another 

 place (see Art. I. p. 281.). — J. R. Hevenoaks, May, 1840. 



Mr. Pernios Mode of Warming and Ventilating. — The fair and open manner 

 in which you admit the suggestions of correspondents, although opposed to 

 your own opinions, induces me to offer a few observations on the improve- 

 ments in hot-water apparatus published in the last two Numbers of your valu- 

 able Magazine ; and, first, allow me to make a few remarks on [We have 

 omitted those on the expression " inverted cylinder," because, as appears at 

 p. 272., it is simply an error of the press] Mr. Beaton, who thinks he ought to 

 have found out Mr. Penn's method of ventilating hot-houses some years ago. 

 I quite agree with him in this, and think he has a very fair claim to divide the 

 palm with Mr. Penn ; his experiment being equally as original as the other ; 

 and both their discoveries are as novel as the introduction of chimneys, which, 

 I think, antiquarians refer to about the thirteenth or fourteenth century. 

 There is, in fact, nothing whatever that is new in this circulation of air ; the 

 very same cause which produces the draught of air up a heated chimney causes 

 the circulation in Mr. Penn's system, and also was the cause of the phenome- 

 non which Mr. Beaton describes (p. 229.) ; and it appears to me perfectly ab- 

 surd to suppose that by the former of these modes the air is prevented from 



* A statement of the quantity of heat which may be obtained from a given 

 quantity of fuel consumed in one of the three boilers, will be found in our 

 April Number, and this is probably the purport of W.'s query. 



