6'20 PHILOSOPHICAL TKANS ACTIONS. [ANNOjJSa, 



degree of heat equal to i80 of Fahrenheit; that it is convertible into a red 

 acrid substance by cxposnre to a higher degree of heat, from wliich, as in the 

 former instance, liquid quicksilver may again be obtained by simple distillation; 

 and that, contrary to what the alchemists have pretended, by no operation of 

 fire is quicksilver convertible into gold or silver.* 



/i Spirit Level to be fixed to a Qiiadra7it for taking a Meridional Altitude at 

 Sea, when the Horizon is not visible. By, John Hadley, Esq. V. Pr. R. S. 

 N° -130, p. 167. 



The necessity of seeing the horizon, in order to find the latitude of a ship 

 at sea, has always been so great an inconvenience, that any method for deter- 

 mining it without the help of the horizon, will be of considerable use, though 

 it should be liable to an error of a few minutes; and as it is generally agreed 

 by seamen, that they are much oftener sensible of this inconvenience in calm 

 weather than in rough; it is hoped that the following manner of constructing 

 and using a spirit level, may in that case be capable of so much exactness, at 

 least, as may render it acceptable to the public. 



This level, fig. 6, pi. 15, is composed of a glass tube ab, bent into an arch 

 of a circle, and containing such number of degrees as will be most suitable to 

 the degree of exactness with which the observation can be made. Its bore 

 must not be wider than the 10th of an inch in diameter, that the liquor in 

 it may the better keep together, and its two ends stand perpendicular to the 

 tube in all positions: nor should it be much less, lest the hanging of the spirit 

 to the sides hinder it from settling so truly by its weight to the lowest part of 

 the tube. This tube is cemented into another brass one cdef, of the same 

 curvature, the outer half of which is taken off, to show the glass, leaving only 

 a small part in the middle df entire, in which a small stop-cock g is placed. 

 The glass tube is divided in two in the iniddle, to make room for this stop- 

 cock, the key of which must be pierced through with a hole of only about -pi-,- 

 part of an inch, for the passage of the liquor. The outer ends of the glass 

 tube must have a conmiunication with each other round about by means of two 

 small pipes i and k, and the tube h, the manner of which is sufficiently shown 

 by the figure. 



Each half of the glass tube ab must have a scale of degrees, answering the 

 curvature of the tube, subdivided at pleasure. They may be numbered either 

 as the upper or under scale in the figure; and observe that in the under scale 



• A continuation of these experiments is inserted in the next, (i. e. the 39th,) vol of the Phil 

 Trans. 



