Page:A Voyage of Discovery and Research in the Southern and Antarctic Regions Vol 1.djvu/430

330 Observations were made at the summit of Pico Ruivo, at intervals of ten minutes, during 1½ hours, viz. from ½ past 7 to 9, simultaneously with those of the standards on the shore, six feet above mean tide.

Whence by Bessel's Tables (Sci. Mem. vol. ii. art. xvi.) we find the height equal 6089.08 English feet, if .00375 (Gay Lussac's determination of the volume of air at 0° C.) be taken as the measure of its expansion for each degree of the centigrade thermometer, and 6094.90 feet, if .003648 (Rudberg's determination) be taken.

The cisterns of the standard barometers were 6 feet above the sea; therefore 6 feet is to be added for the height of the summit of the peak, making the above numbers 6095.08 and 6100.90 feet.

"My dear Ross,

"Mr. Bowditch was, I believe, the first to notice that the height which I had assigned to the Pico Ruivo, from the barometrical observations which were made by Captain Clavering and myself during our short stay at Madeira in the winter of 1821–1822, was some hundred feet less than the true height of the peak, as measured by himself a few months after we had visited the island. A similar notice has recently been made by Lieutenant Wilkes, the American navigator; and the observations of Wilmot and Lefroy, which you are about to publish, bear full