68 Barometric Measurement of Sugar-loaf Mountain j 



rise, and which has enabled him to ascertain satisfactorily the 

 elevation at which that river originates its yet unknown course. 

 The accordance of the portable barometer with the stationary 

 was examined before and after the observations for the measure- 

 ment; the latter was placed in the room in Fort Thornton^ in 

 which my pendulum experiments were made, and its height, 

 consequently, above half tide, carefully ascertained by levelling/ 

 was known, with tolerable precision, to be 190 feet; the varia- 

 tions in the density and temperature of the atmosphere, and in 

 the point of deposition of moisture as indicated by your hygro- 

 meter, were observed at this spot by Captain Laing, at stated 

 periods with a chronometer, on the 28th of March, so as to be 

 simultaneous with such as should be made at elevations. 



I shall confine myself to stating the data necessary for the cal- 

 culation of the heights of the clergyman's house at Regent-town, 

 and of the summit of the Sugar-loaf. At the first of these sta- 

 tions, the barometer, having been suspended above an hour five 

 feet below the gallery which surrounds the clergyman's house, 

 shewed at 7 A.M. on the 28th March, 29.017 in., tb. 74°.5, and 

 the point of deposition 57° ; the corresponding observations at 

 Fort Thornton were 29.820 in., th. 79°.5, and the point of depo- 

 sition 66°. At 1 1 A.M. on the same day, the barometer being^ 

 suspended in the shade, at the summit of the Sugar-loaf, the 

 cistern \^ feet below the highest point, was suffered to remain 

 until 12 o'clock, that the mercury might acquire the tempera- 

 ture shewn by the attached thermometer ; when the observations 

 registered were 27.560 in., th. 82°.2, and the dew point 70°, — 

 those at Fort Thornton being 29.795, th. 84°, and the dew 

 point 70°, also. 



The mercury bemg reduced to the same temperature at the' 

 upper and lower stations, and -^-^ of the differences in the 

 heights of the column being added on account of the respective 

 diameters of the tube and cistern of the barometer, the true 

 dififerences are, between Fort Thornton and Regent-town .8 in., 

 and between Fort Thornton and the Sugar-loaf 2.263 in., at the 

 temperatures of the air, and under the pressure of the amount 

 of atmospheric vapour specified above. The approximate heights 



