The Black Bulb Thermometer 



113 



temperature they had registered during the previous twenty- 

 four hours, were read every morning at nine o'clock. Read- 

 ings were also obtained at various times throughout clear 

 days so as obtain their indications at other periods than 

 those of maximum radiation. 



No. 4. Thermometer by Negretti and Zambra, of London. 

 Black glass bulb. 



Nos. 1 and 2 are enclosed in outer protecting tubes of 

 glass, exhausted of air and hermetically sealed ; the enclosing 

 bulbs are about one -inch diameter. 



In Nos. 3 and 4 the enclosing tubes are larger than 1 and 

 2, and are from one-and-a-half to two-and-a-half inches 

 diameter. 



No. 4 was compared at Greenwich, and is certified to be 

 correct from 32° to 100°. 



In the first place, all these thermometers were compared in 

 heated water with a standard thermometer, and found to 

 have similar corrections amongst themselves at high tempe- 

 rature as at low ones. 



These readings were tabulated and the results are as 

 follows : — 



No. I. 



No. 2. 



No. 3. 



No. 4. 



Lampblack Bulb. 



JB. Glass. 



B. Glass. 



B. Glass. 



When No. 1 reads from. 



Correction. 



Correction. 



Correction. 



60° to 70° 



— 3-3 



-f 0-7 



— 0-7 



70 to 80 



— 5-3 



+ 2-1 



— 1-2 



80 to 90 



— 8-1 



4- 5-1 



— 0-9 



90 to 95 



— 9-8 



4-14-9 



— 2-2 



95 to 100 



— 11-3 



4- 14-1 





-1-8 



100 to 105 



— 11-6 



4-14-5 



- 



-0-9 



105 to 110 



— 12-0 



-ll4-l 





-0-4 



110 to 115 



— 11-1 



4- 14-9 

 4-13-7 



- 



-0-1 



115 to 120 



— 12-4 



— 0-8 



120 to 130 



— 12-9 



-f 12-6 



— 1-3 



130 to 140 



— 13-7 



4-io-o 



— 2-8 



I then tried them by exposing them to heat radiated from 

 a dark body, thus : A sheet of copper, one foot square, with 

 a dull surface, was placed perpendicularly, and a large 

 Bunsen's burner made to play on one of its surfaces, so as to 

 heat it at about the centre. Thermometers Nos. 1 and 2 

 were now arranged on a stand, so that their bulbs were 

 both as nearly as possible three inches from the centre of the 



K 2 



