Retrospective Criticism. 285 



standard; and, in 1808, when the temperature in London was 93'5°, the 

 average was only 30'5°. Therefore, taking these as facts, and considering the 

 almost impossibility of ascertaining the exact temperature during a year, I, as 

 already stated, considered that, for every practical purpose, it is sufficiently 

 accurate to assume they are invariably alike ; and, as every created thing bears 

 the indelible stamp of design in its creation, it seems unlikely any thing so 

 truly important should be left to chance. Now, these statements are either 

 founded in error, the years sadly changed, or N. mistaken ; and, until I am 

 better informed, I must consider the latter to be the case. But I should like 

 to see the correctness of the statement discussed by those able to do so. It 

 seems to me surprising that instruments better calculated to ascertain the 

 temperature have not been produced, as a thermometer that would register 

 the temperature of every hour might easily be invented. N. differs from me 

 also upon acclimatising plants. He considers their nature immutable, yet he 

 overthrows the proposition by stating that in successive generations we can 

 do a little; but grant that the progeny of a plant can be rendered more hardy 

 than its parent, and the same rule must be applicable ad injinitum, — X. M. T. 

 Folkestone, Ajml 3: 1841. 



j\Ir, Penn's ]\'Iode of Heating and Ventilating, (p. 232.) — It appears to me 

 that G. C, in noticing Mr. Penn's mode of heating, has gone rather too far, and 

 admitted a little more of the truth than he intended. The upward air, he says, 

 amounted to an agitating current. Without a downward current, how was 

 the upward one supplied ? This unhappy admission of fact has established 

 what he so anxiously wished to disprove. Next time he catches a frosty day 

 let him hold a lighted candle in the drains, and he will be convinced there are 

 more currents than the upright ones. — N. M. T. April 7. 1841. 



Mr. Forsi/tlis Plant Structures. — Mr. Forsyth, in p. 204., refers with much 

 seeming satisfaction to the gloomy structures he has recommended (Vol. XIII. 

 p. 62.) for the culture of plants, which reminds me that I intended entering 

 my protest against all such pseudo-economical structures, and cautioning the 

 inexperienced against erecting them, as the result must be inevitable disap- 

 pointment. I am now, despite of previous prepossessions to the contrary, 

 convinced that they are altogether unfit for the purpose of exotic culture 

 during the months of winter. The inelegant appearance of the houses re- 

 commended in Vol. XIII. p. 204. would deter most people from erecting 

 them, were they not held forth as economical ; but a trial will prove this to 

 be an utter fallacy, as I calculate they require at least one third more fire than 

 houses having front or upright glass, upon which the sun can act at a season 

 when his oblique rays are utterly powerless upon houses without it. At a 

 time, too, when the influence of light is universally known to be indispensable 

 to the progress of vegetation, it seems incredible that any one should so far 

 expose himself as to advocate structures that go so far to exclude it. Light 

 is, in fact, the only difference in artificial climates between summer and winter, 

 and the progress made by vegetation is in proportion to its intensity, showing 

 it to be an essential which no artifice can supply ; consequently, a house con- 

 structed to admit a single ra}' more than another is the more perfect, and 

 vice versa. Mr. Forsyth commiserates the amateur who possesses detached 

 houses with glazed ends, glass doors, partitions, &e. ; still these houses, shed- 

 like though they be (but appearance can have no effect upon the man who 

 admires brick fronts, brick ends, and brick partitions), yield to none in their 

 fitness for the culture of plants. Being detached, enhances their real value, 

 as they enjoy several hours more direct sun than they otherwise would, and 

 the advantage of this, economy apart, will not be denied by any who admit 

 the powerful agency of light. Such structures would be considered more 

 perfect by the " ridiculous foolery of glazing the dead north wall," p. 204., as 

 this would put plants in the position assigned them by the hand of the " Glo- 

 rious Architect Divine ;" placed, as it were, in a centre of light, without which 

 they are apt to become, hke Mr. Forsyth's structures, terribly one-sided ; and, 

 however contemptible he may deem the pale blue rays of the north, still, when 



