512 Mr. A. W. Warrington on 



C. On the Thermometer used. 



The thermometer, no. 11806, was made by Tonnelot, and 

 was calibrated and examined at the "Bureau International 

 des Poids et Mesures " at Paris. By the great kindness of 

 M. Guillaume I was enabled to obtain possession of this 

 instrument at very short notice. 



Table VII. gives the zeros corresponding to prolonged 

 exposure to the temperature of melting ice on the days 

 mentioned. The fourth column gives the zeros calculated by 

 the method of least squares, and assuming the rise of zero may 

 be expressed as a function of the time in the form 



z = a + bA + cA' 2 , 



where z is the zero and A* the time in days. The zero- 

 correction for every experiment was calculated from this 

 formula, the values for a, b, and c being respectively +0 0878, 

 + 0-000057, and -0'00000005. The probable error of a 

 single determination being ±0 O- 0021. 



All the readings were reduced to the scale of the " Paris " 

 hydrogen standard. 



D. On the Water used. 



The water, already very pure, was slowly distilled from a 

 copper still lined with tin, the steam being condensed in a 

 worm of block tin. The water was collected and preserved 

 in a large flask of Jena glass and used within a day or two 

 of preparation. The water was rendered air-free by boiling, 

 and afterwards allowed to cool in the hermetically closed flask. 



E. Detailed account of Experiment 39 (made Mar. 23, 1898). 



The hydrometer loaded with platinum ring weights, which 

 weighed 1*40483 grammes in the air, was placed in the dis- 

 tilled water, and the following observations of the temperature 

 of equal density made. 



[Table pp. 514, 515.] 



Beduction of Observed Temperature to the "Paris" 

 Hydrogen Standard. 



The division marking the 22nd degree was coincident with 

 the surface of the water ; hence a column of mercury equal in 

 length to 3 degrees was exposed to a temperature varying 



* This A is not the same as the A in Tahle III., Appendix H. 



