416 Olservaliolis respecting 



ings with putrescent animal and vegetable matter ; from a mix- 

 ture of which kind, after exposure for a sufficient length of time 

 to the action of the air, a quantity of nitre may usually be ob- 

 tained by lixiviation : but it would be a question of mere curio* 

 sity, on this occasion at least, to investigate the origin of the 

 practice. The intention of the present paper is to state the re- 

 sult of a series of observations made during the last year, on the 

 connexion that exists between the natural production of nitre 

 and the slate of the atmosphere. In detailing these observa- 

 tions, it will be convenient to give previously a description of the. 

 laboratory of the Ashmole Museum, in which building they were 

 principallv made: nor shall I be afraid of being thought too 

 minute in this description, or in any other part of the following 

 detail, by those at least who know tiie precision that is requisite 

 in every induction, which like the present rests on phaenomena 

 of an obscure and equivocal nature. 



The Ashmole Museum, which was built by Sir C. Wren in 

 the reign of Charles the Second, is an insulated building, con- 

 structed entirely of calcareous freestone, and consisting of three 

 stories. The lowermost of these stories was originally designed 

 for, and has constantly been used as, a chemical laboratory. 



The pavement of the laboratory, on its eastern, northern, and 

 vvestern sides, is about nine feet below the level of the street in 

 which the Museum stands ; on its southern side it is on the 

 same level with an area, about ten feet in breadth, which in 

 part occupies the site of the ditch of the old town, and insulates 

 a quadrangular projecting part of the whole building of the 

 Museum. The laboratory itself is a single room sixty feet in 

 length from east to west, and twenty-five in breadth ; having an 

 arched stone ceiling, the centre of which is seventeen feet above 

 the level of the pavement. The walls of this room, which are 

 nearly three feet in thickness, are constructed of squared cal- 

 careous freestone, which I have reason to believe was dug from 

 a quarry near Burford, and is technically called Windrush stone, 

 from the river of the same name. There are four windows in 

 the upper part of the north side of the laboratory, formed in the 

 curve of the arched ceiling ; the dimensions of each of which 

 are five feet by four and a half. 



There is no window either on the eastern or western side of 

 the laboratory. 



On the south side lihere are two windows, one at each ex- 

 tremity, looking into the area above described ; and these win- 

 dows are placed at the usual distance from the ground, that is, 

 about three feet : and all that part of the south side interme- 

 diate to these two windows separates the laboratory from the 



quadrangulac 



