IJg 8TAT« or VAPOUK IN THB ATMOSPHERE. 



dace the fpace to about three centimetres (about an inch,) It 

 muft be thus continued to within one decimetre of the edge of 

 the boiler ; and muft then be brought into conta6l with it. D is 

 an aperture of two decimetres wide by one in height (about eight 

 inches by four) communicating with E. But at the fide of the 

 angle a, this pafTage for the heat muft be made of one metre 

 (three feet three inches) in width, by one decimetre (about 

 four inches) in height, and this proportion continued to the 

 aperture E. 



F is a fecond boiler, intended to be heated by means of the 

 excefs of heat from the firft; many others may be applied in 

 fucceffion, if required. G is an aperture with the fame pro- 

 portions as D. At the angle b, it muft be obferved to make 

 the aperture of the chimney five decimetres by two (19| inch. 

 by 7| inch.) and to continue this proportion to about two thirds 

 of its height. The aperture may then be contrafted fothat, at 

 its upper extremity, it may not be lefs than one decimetre by 

 three (about four inches by twelve.) This part of the chim- 

 ney (hould be fo conftru6ted as to be able to clofe it conveni- 

 ently, when required. 



XI. 



CorreSHon of a Mijiake in Dr. Kinvan's EJfay on the State of 

 Vapour in the Atmofp/iere. By Mr. Dalton. 



To Mr. NICHOLSON. 

 SIR, 



Ki'rwanmquot- -^ TAKE the liberty of requefting you to corred a miftake in 

 ingMr. Crof- Dr. Kirwan's eflay on vapour, copied in your laft number, 

 JftylS a m"xu' P^S^ 246. In treating upon the height of clouds, he obferves, 

 mum heightof " In lat. 54-**, in Cumberland, Mr. Crofthwaite obferved none 

 the clouds. „ lo^.^r than 2700 feet, and none higher than 3150, in the 

 " courfe of feveral years." For this he refers to my meteoro- 

 logical obfervations, page 41. The fadls there ftated, how- 

 ever, are fo very different from thofe above mentioned, that I 

 conclude Dr. Kirwan has not feen the book, and has been 

 mifinformed. The account referred to is, that Mr. Crof- 

 thwaite obferved the heights of the clouds ufually three times a 

 day for five years, by remarking their interfedion with Skid- 

 daw (a high mountain near Kefwick.) The refult was, 



4 Clouds 



