ARTIFICIAL HORIZON. 



sudden condensation. From Mr. Dalton's experiments, 

 (see pin- Journal, vol. Ill, p. l6o) it appears, that the con- 

 densation answering to the pressure of our atmosphere af- 

 fords an increase of temperature upwards of 50 degrees; 

 and, if we suppose this augmentation to be in the simple 

 ratio of the compression, though it is probably higher, a 

 compression of 18 atmospheres would give" the temperature 

 of ignition. 



S79 



VII. 



Description of a portable artijicial Horizon for faJdng Al^ 

 titudes at Sea or Land, by Mr. Wright. In a Ltttef 

 from the Invaitor. 



Sir, 



JL Beg leave to transmit you a description and delineation Artificial hori 

 of an artiticial horizon, which I conceive will be found pre- 2011 described. 

 ferable to any other in use. 



Plate VII, fig. 1, represents the hoi-izon with all its parts 

 complete: fig. 2, a cylindiic vessel of brass, to be filled with 

 water when in use: fig. 3, the upper part of the horizon 

 taken from the vessel, to show its intenial parts. A A are 

 two uprights of brass and a horizoatal axis on the top, 

 with two fine edges at BB, on which the brass frame CC is 

 suspended. ' At the bottom of the frame are an index and 

 two siglits; the nearest sight E having a fine horizontal 

 edge on its top, and on the farthest sight F is a fine black 

 line in a piece of transparent ivory. The index is adjusted 

 to a horizontal position by two screws, which fasten it also 

 to the frame when adjusted ; on the index is a conyex glass 

 to magnify the line on the ivory sight F, and throw its image 

 on the edge of the sight E; and under the index, in its 

 jcentre, is screwed a thin brass blade H, to be immersed in 

 the water in the vessel, fig. 2, for the purpose of preventi.ng 

 the horizon from getting any vibrating or pendulous motiou' 

 '..."' to 



