536 



MR J. Y. BUCHANAN ON 



iii order that the single divisions should not be too far apart it would have had to be 

 divided into twentieths of a degree. 



The other thermometer, B, was especially made with a view to experimenting on 

 chloride of sodium at all available heights above the sea. It was graduated into Centi- 

 grade degrees and tenths, the length of one degree being 10 mm., and the range was 

 from 85° C. to 110° C. 



By the kindness of Dr Bilwiller, director of the Central Meteorological Office of 

 Switzerland, I was able to compare the indications of this thermometer in saturated 

 steam at different heights with the temperatures which it ought to have shown, on the 

 basis of the atmospheric pressure as given by the barometers of the central bureau at 

 different stations. For higher temperatures it was verified in terms of the standard 

 barometer of the Scottish Meteorological Society in Edinburgh, which was obligingly 

 put at my disposal by Dr Buchan. The following are the readings in the order of 



height : — 















Locality. 



Julier. 



Sils. 



Zurich. 



Edinburgh. 





Height above sea, . 

 Barometer, at 0° C, 

 Observed temperatures, . 

 Calculated do., 

 Correction, .... 



metres, 

 mm. , 



2244 

 581-84 

 92-86° C. 

 92-69° 

 -0-17 



616-4 

 94-38° 

 94-24° 

 -0-14 



720-3 

 98-62° 

 98-51° 

 -0-11 



76418 

 100-23° 

 100-16° 

 -0-07 



Thermometer B was compared at Kew, giving corrections amounting in the extreme to 

 0"2 C F. All the observed temperatures have been corrected accordingly. 



The General Order of the Experiment. — The temperature of saturated steam was 

 determined in the straight steam tube. The U-shaped receiver being clean and dry, was 

 weighed. The portion of salt, usually one-fifth of a gramme- molecule, was weighed out 

 carefully into the receiver, which was then again weighed for the purpose of afterwards 

 arriving at the weight of the condensed steam. The weight of the receiver, both empty 

 and charged, includes that of the thermometer and its attachment. When steam is issuing 

 from the boiler at the top of the T tube, the receiver is connected with it, as shown. 

 The top of the T tube is now closed with the cork, and the passage of steam through the 

 salt begins. The time is noted when the steam reaches the salt, and this is the begin- 

 ning of the experiment, and the time is logged as a part of every entry in the note-book. 

 It is particularly noted when the mass in the receiver forms a liquid magma through 

 which the steam bubbles, when the thermometer attains its maximum, when it begins 

 to be unsteady, and when steam is shut off. Before reaching the maximum the tem- 

 perature is noted every half-minute, afterwards every minute, and at the end every half 

 or quarter minute. When it is judged by the fall of temperature and the quantity 

 of salt undissolved that these two small quantities compensate each other, the cork is 



