. I 1 

 > i> 1 



3 3 ) } 



Observations made ivith a Black Bulb Thennomeier, 



•91 I :::,:': 



cases, but the amount of cloud and the relative humidity each differ 

 by 13 per cent. High temperatures and great temperature-dif- 

 ferences are preceded by morning dew or frost not more than once 

 in five times, while thunder and lightning follow, in the afternoon 

 or evening, once in three times. Dust has evidently more con- 

 nection with high temperatures than with great temperature 

 differences. 



Scott has remarked that the highest observed temperature in the 

 sun of which he had heard was 215° at Leh, and not infrequently, 

 in Tibet, observations had been taken ranging above the boiling- 

 point of water to the height of the place. * It seems to me to be 

 exceedingly doubtful if such high temperatures as these could pos- 

 sibly be registered by a black bulb in vacuo exposed in the orthodox 

 way. By suitable artifice they may, of course, be obtained. Thus 

 Blanford mentions that Dr. Cayley succeeded in making water boil 

 at Leh, 11,500 feet above sea-level, by exposing it to the sun in a 

 small bottle blackened on the outside and placed inside an empty 

 quinine phial to protect it from the wind.f Again, by placing an 

 open black bulb thermometer in a wooden box lined with velvet and 

 covered with a sheet of plate glass, it is possible to obtain a tem- 

 perature of 200° to 250° in the sun. De Saussure, with a wooden 

 box lined with blackened cork and covered with three sheets of 

 glass, obtained 190°.]: Langley, on Mount Whitney, in September, 

 1881, with his "hot box" obtained 236°. § J. Herschel using a 

 similar apparatus obtained 248° at midsummer, at the Cape, and 

 even cooked eggs, fruit, meat, &c, with it; he remarks that by 

 suitable precaution a temperature approaching to ignition mighii 

 readily be commanded. || All these cases, however, represent 

 accumulated, not instantaneous, solar radiation. The highest 

 black-bulb temperature obtained by Dr. Scully in Western Tibet 

 during the summer of 1875, at any altitude exceeding 10,000 feet, 

 was 147 0, 5. And even this, together with some others of 130° to 

 135°, at the same high altitudes, " are probably attributable to the 

 radiation received from the rocky sides of the valleys." If 



* E. H. Scott, Q. J. Met. S., April, 1873, p. 171 ; also the same author's 

 "Elementary Meteorology," 1893, p. 56. 



f H. Blanford, "Climates and Weather of India," p. 2. The boiling-point at 

 this altitude is about 192°. 



{ See J. Forbes, " Transparency of the Atmosphere," Phil. Trans., 1842. 



§ S. P. Langley, " Kesearches on Solar Heat," p. 167. 



|| J. Herschel, "Results of Observations at the Cape of Good Hope," Appendix C, 

 p. 444. 



11 H. Blanford, Indian Met. Memoirs, vol. i., p. 220. 



