Messrs. C. W. Waidner and F. Mallory on 



From a series of direct comparisons of the mercurial 

 thermometers with a standard air thermometer, a number of 

 equations of the above form were obtained, from which the 

 most probable values of these constants were deduced by the 

 method of least squares. 



From these formulas tables were constructed giving the 

 temperature on the scale of the standard air thermometer 

 corresponding to each centimetre of the stem. These tables 

 are found on pp. 115 & 116, Proc. Amer. Acad. xv. 1879. 



These thermometers were always used with a constant zero 

 determined before each series of observations, by immersing 

 the thermometer in a mixture of finely cracked ice and distilled 

 water for a period of one or two hours. As the position of 

 the zero, owing to the imperfect elasticity of the glass, depends 

 on the temperature to which the thermometer has been sub- 

 jected recently, the thermometers were always kept at least 

 one week at a temperature of about 20° C. before they were 

 used in a comparison, or in a determination of the mechanical 

 equivalent, in which interval the zero will have almost 

 recovered from the depression due to a recent heating of the 

 thermometer. 



In the original comparisons of these thermometers with the 

 air thermometer, no corrections were necessary for internal 

 pressure due to the mercury column and meniscus, as the 

 thermometers were compared and always used in a vertical 

 position. A correction for external pressure was made, due 

 to about 60 cms. of water in the comparison tank. 



In the experiments on the mechanical equivalent, the ther- 

 mometer was placed in the calorimeter with the top of the 

 bulb about 5 cm. below the surface of the water, and the 

 remainder of the stem projected out into the air. The stem 

 correction was then applied in two parts by surrounding the 

 stem, where it projected from the calorimeter, with a small 

 water-jacket, the remainder of the stem being assumed to be 

 at the temperature of the surrounding air. 



Platinum Thermometry. 

 The measurement of temperature by means of the variation 

 of resistance of a wire was first seriously proposed by Siemens, 

 who submitted for trial to a committee of the British Asso- 

 ciation some platinum-resistance pyrometers (Brit. Assoc. 

 Report 1874). The results of these experiments were unfa- 

 vourable to the use of the platinum-resistance thermometer as 

 a scientific instrument of precision. It was found that, for 

 this type of pyrometer, the resistance of the platinum wire was 

 not a constant for a fixed temperature, but depended greatly 



