VOL. LXXXII.] PHILOSOPHICAL TRANSACTIONS. 140 



To settle the position of the base, says Mr. T., with respect to the meridian, 

 the sun's bearing from each signal, and his azimuth, were observed several times, 

 both with the theodolite and the Hadley; and having made the necessary com- 

 putations, I became satisfied of the justness of an opinion I had before enter- 

 tained, that the Hadley is by far the best instrument in general practice for such 

 purposes; for though the theodolite has the advantage, from its fixed position, 

 and the power of its telescope, in taking horizontal angles on the horizon; yet 

 at any considerable elevation, when a strict attention is required to the vertical 

 adjustments of the theodolite, such attention is incompatible with the nature of 

 a portable instrument, which is ever liable to suffer change in its adjustments by 

 even the most careful removal from place to place. Having completed the mea- 

 surement and principal calculations, I caused a large stone to be placed at each 

 extremity of the base, to mark and perpetuate it for future occasions, both in- 

 scriptions equally implying, that the opposite end of the base line lies in the 

 direction therein expressed, distant ] 1,636 English yards from the stone so 

 inscribed. 



FII. Description of Kilburn JVells, and Analysis of their tVater. By Mr. 



Joh. Godfr. Schmeisser. p. 115. 



Kilburn wells lie to the right of the Edgeware road, about 1 miles from Lon- 

 don, in a dry, but verdant, and gently rising meadow. They spring about 12 

 feet below the surface, and are covered with a small stone cupola. The diameter 

 of the well near the surface of the water is about 5 feet; the depth of the water 

 was in July and August 2 feet; this its general depth increases in winter, at times, 

 to 3 feet; the changes in the atmosphere do not appear to affect either the quan- 

 tity or quality of the water. 



This mineral water is not perfectly bright, but of rather a milky hue; it has 

 a mild and bitterish taste, with little or no briskness, as containing a very small 

 proportion of fixed air. On dipping for the water, or otherwise agitating it, a 

 sulphureous smell is perceived near the surface; which however soon goes off in 

 a temperature of about 80° of Fahrenheit's thermometer.* The specific gravity 

 of the Kilburn water is to distilled water as 1.0071 : 1.0000; its general tempe- 

 rature 53°, which was not affected by a change of 10° in the temperature of 

 the atmosphere. While the water continues at rest, no bullition of fixed air is 

 perceived, and scarcely any sulphureous smell. That this mineral water so easily 

 parts with the hepatic air, perceivable on agitating it, when shaken in a warmer 

 temperature, or transported from one place to another, is probably owing to the 

 fixed air it contains: for as this aerial acid has a great affinity to phlogiston, so 

 it may hence be inferred, that fixed and hepatic air . cannot exist together in a 

 * This thermometer was used by Mr. S. in all these experiments. 



