45, COKNHILL, E.G., AND 122, EEGENT STREET, W., LONDON. 93 



To use the Boiling Point Apparatus, it is simply necessary to pour into the 

 boiler, through the small opening (F) on its surface, a sufficient quantity of 

 water to fill it about one- third, and afterwards close it by means of the 

 screw for that purpose ; the lighted spirit lamp is then applied, and when the 

 water is made to boil, the steam rises, surrounding the bulb and tube, and 

 descending between the two tubes, issues from the opening at (G.) After a 

 few seconds, the mercury in the thermometer will rise and become stationary ; 

 the degree indicated by it must then be noted, when, by reference to the tables, 

 the elevation of the spot where the experiment has been performed may be 

 obtained. 



The Temperature of the Air should be observed by a reliable Thermometer 

 at the same time. Price, with Spirit Lamp, in Sling Case, 550 



Extra Standard Thermometer . 1 10 

 Extra Thermometer for Air Temperature . 10 6 



The following table expresses very nearly the elevation in feet correspond- 

 ing to a fall of 18 in the temperature of boiling water : 



Boiling Temperatures Elevation in Feet 



between for each Degree. 



2H Q and 210 520 



210 and 200 530 



200 and 190 550 



190 and 180 570 



Mule for computing heights from observations rvith the Boiling Point Apparatus or Mountain 



Thermometer, by Negretti and Zambrd's Boiling Point Tables. 



From Table I. take out the heights in feet corresponding to the boiling-points observed 

 at the upper and lower stations respectively. The difference between these two numbers, 

 multiplied by the factor in Table III. for the mean temperature of the air, is the difference 

 in height required. 



EXAMPLE : 



At upper station, boiling-point = 187'3 ; temp, of air = 26. 

 At lower station, boiling-point = 210 -4 ; temp, of air = 68. 

 Boiling-point = 187'3 ; height from Table I. = 13495 feet. 

 Boiling-point = 210 4 ; height from Table I. = 905. 



Difference =12590 



Mean temp, of air = 47 ; factor from Table III. 1-033. 



Kequired difference between the two stations = 12590 X 1'033 = 13005 feet. 

 To determine a height with accuracy, it is necessary that pure water should be used, 

 distilled water if possible, and a similar observation should be made at the same time at a 

 lower station, not very remote laterally from the upper, and both should be many times 

 repeated. When such observations have been very carefully conducted, the height of the 

 upper station above the lower may be ascertained with great precision, as has been 

 repeatedly verified by subsequent trigonometrical measurement of elevations so determined. 

 If the lower station be at the sea level, the absolute height of the upper is at once obtained. 



