_Example, in calculating Heights from the Observations of the Boiling-point of Water._--1. At Geneva the observed boiling-point of water was 209 deg.335; on the Great St. Bernard it was 197 deg.64; the mean temperature of the intermediate air was 63 deg.5; required the height of the Great St. Bernard above Geneva. Method by formula:-- _H'_ = _f_ (_B_ - _b_) { 1 + (_m_ - 32 deg.) .002036 } In this case _f_ is between 530 and 550, or 540. _B_ = 209.335 _m_ = 63.5 _b_ = 197.64 32 ------- ----- 11.695 31.5 _f_ = 540 .002036 ------- --------- 6315.3 0.0641340 1.064 1 ------- ----- _H'_ = 6719.5 feet. 1.064 ====== Method by Tables supplied with boiling-point apparatus made by Messrs. Negretti and Zambra:-- 209.335 gives 1464 in Table I. 197.64 " 7736 " ---- 6272 63.5 " 1.07 in Table II. ---- Height 6711 ==== =96. Thermometers for Engineers.=--_1st. Salinometer._--Under the circumstances at which fresh water boils at 212 deg., sea water boils at 213 deg.2. The boiling temperature is raised by the chemical solution of any substance in the water, and the more with the increase of matter dissolved. From a knowledge of this principle, marine engineers make use of the thermometer to determine the amount of salts held in solution by the water in the boilers of sea-going steamers. Common sea-water contains 1/33 of its volume of salt and other earthy matters. As evaporation proceeds, the solution becomes proportionally stronger, and more heat is required to produce steam. The following table from the work of Messrs. Main and Brown, on the Marine Steam-Engine, shows the relation between the boiling-point under the mean pressure of the atmosphere, or 80 inches of mercury, and the proportion of matter dissolved in the water:--