45, COENHILL, E.G., AND 122, EEGENT STREET, W., LONDON. 



35 



earth are widely separated from each other, and the range of the thermometer 

 is always greatest in the interior of the continents within the tropics. Mr 

 Campbell, in the country of the Botchuanas, saw the thermometer at 8 a.m. at 

 28, and at 84 at noon. Mr. Bruce records a temperature at Gondar of 113. 

 The thermometer at Benares rises to 118 ; at Sierra Leone the thermometer on 

 the ground has been seen to rise to 138 P , and Humboldt gives many instances of 

 the temperature of the torrid zone rising to 118, 120, and 129. At one time 

 he found the temperature of a loose, coarse-grained granite, in the sun, 140'5. 

 In the Dukhun at a height of 3,090 feet above the sea, Col. Sykes once saw the 

 thermometer in the shade at 105, the range of the thermometer generally being 

 from 93.9 to 40^.5." 



Slightly beneath the surface of the earth in the tropics, Humboldt states 

 temperatures of 162 and 134 are frequently noted, and in white sand at 

 Orinoco 140, whilst at the Cape of Good Hope under the soil of a bulb garden 

 a temperature of 150 is recorded by Herschell. In China, the temperature of 

 water of the fields was found to be by Meyer 113 and adjacent sand much 

 hotter. These extremes of temperature, which would cause the specific gravity 

 of the air to vary from 1167 to 863, may serve as a kind of measure of the dis- 

 turbing causes which interfere with the velocity and local direction of atmos- 

 pheric currents and other phenomena, the calculation of which has been founded 

 upon mean results. DanielVs Meteorology. 



It is stated that below the layer of constant temperature (estimated at about 

 80 to 90 feet from the earth's surface), the temperature is found to increase one 

 degree Centigrade for every 100 feet. 



46. Earth Thermometer, Symons' Arrange- 

 ment, with NEGUETTI & ZAMBBA'S Slow Action 

 Thermometer. An iron tube closed at the lower end 

 is forced down into the earth, and secured at the 

 desired depth, and the thermometer lowered down 

 into it by a cord or chain to the bottom, and allowed 

 to remain a sufficient time ; when the temperature is 

 to be noted, it is quickly drawn up and its indication 

 observed. The great advantage of this method of 

 obtaining Earth Temperatures is that the ther- 

 mometer can at any time be compared with a Standard, 

 which is a difficult if not almost impossible operation 

 to be carried out with Thermometers of great length 

 (fig 39). Also see fig. 49, page 42. 



Price, according to length, 110 150 



1 10 0, 2 2 0. 



By means of these instruments it has been found 

 that variations depending on the hour of the day are 



D2 



FIG. 39. 



