272 



jRelrospectwe Criticism. 



and soft soap), by Mr. Sliarpe, Pitfour ; on the cultivation of Chrysdnthemum 

 sinense, by Mr. Macintosh, Archerfield, who excels in the management of that 

 splendid winter flower ; and remarks on the most hardy and productive fruit 

 trees known in Lancashire, by Mr. Garnett of Clitheroe. — P. N. 



Art. IV. Retrospective Criticism. 



Erratum. — In p. 229. line 1., for "inverted cylinder" read "inverted 

 cone." 



Remarks on Mr. Penn's Alode of Warming and Ventilating. — The excellence 

 of Mr. Penn's method of warming and ventilating buildings appears to consist 

 in the very uniform degree of moisture which it produces in the atmosphere. 

 The heated air which enters the house has already received a dose of mois- 

 ture nearly sufficient to saturate it, and has not to seek its moisture among 

 the plants, as is generally the case. In most plant-houses the pipes are placed 

 under the front shelves, at a considerable distance from the floor, and the 

 atmosphere is moistened by syringing the plants, or throvi^ing water on the 

 floor and shelves. How greatly the state of an atmosphere so produced differs 

 from that of Mr. Penn's houses, a little consideration of the annexed sketch 

 will show. It is the section of a house heated by pipes under the front shelves; 

 and it must be borne in mind that the capacity of air for moisture varies with 

 its temperature, so that air which was saturated at 56° becomes very dry when 

 heated to 70°. 



The sketch, /g. 41., 

 is the section of a 

 house heated by pipes 

 under the front 

 shelves. The arrows 

 (numbered) indicate 

 the course of the cur- 

 rent of air, AtNo. 1. 

 the air comes heated 

 from the pipes (p) and 

 extremely thirsty ; at 

 No. 2. it finds moisture 

 among the plants, and 

 rising from the damp 

 and warm shelf (slate, 

 of course) ; at No. 3. 

 it has parted with 

 some of its heat ; it is 

 now supersaturated, 

 and is parting with its 

 moisture deposited on 

 the glass ; at No. 4. it 

 is in the same state ; 

 at No. 5. it has ceased to lose heat or moisture; at No. 6. and 7. the same; 

 at No. 8. it again comes within the influence of the pipes, and is heated, 

 becoming again very dry. Now the air which descends to the floor {//), in the 

 first place, is a small and feeble current, and, secondly, is nearly saturated, so 

 that it can take up little moisture ; what little it does get is because the floor, 

 being slightly warmed by the radiation of the pipes, warms, and at the same 

 time moistens, the air; but, nevertheless, the air at No. l.,in which air a visiter 

 walks, is anything rather than saturated. My belief is, that air nearly satu- 

 rated is always agreeable to the feelings. Dry air, which is absorbing moisture, 

 is anything but agreeable. Hence the unpleasant sensation in orchidaceous 

 houses, Now it is unnecessary to show how Mr. Penn's plan obviates all 



