86 



Mr. A. Sworn. 



" Eesearches in Absolute Mercurial Thermometry." By the late 

 S. A. SwoiiN, M.A. Communicated by H. B. Dixon, F.E.S. 

 April 21 — Eead June 15, 1899. 



(Abstract, prepared at the request of the Council by Arthur 

 Schuster, F.K.S., December, 1899.) 



The experimental portion of this work consists of the careful com- 

 parison of six thermometers, with the object of studying the effects of 

 capillarity, and in the second place of obtaining a comparison between 

 thermometers made of English flint glass with those of French " verre 

 dur" or Jena normal glass, and therefore indirectly with the hydrogen 

 scale. 



The instruments emj^loyed consisted of a Tounelot " verre dur " 

 thermometer, to be referred to as No. 4976, an English flint glass 

 (No. 711,179) by J. J., Hicks, two normal thermometers (Nos. 2218 and 

 2219) of Jena 16"^ by Gerhardt of Bonn, and two calorimetric thermo- 

 meters Nos. 2220 and 2221 of Jena 16"^ by Cerhardt, Avith a range 

 from - r to 25° C. 



The Tonnelot instrument is divided on the transparent stem into 

 tenth degrees, and is cylindrical in the bore. The other thermometers 

 have enamelled backs, and are divided on the stem into half milli- 

 metres. At the time the latter instruments were obtained elliptical 

 bores were the only ones procurable, but care was taken that the bore 

 was not unduly flattened, and was smooth in contour. The author 

 considers the readings taken with these thermometers to be quite trust- 

 Avorthy. The ratio of the major to the minor axis of the bore was 

 about 2 for the Jena glass thermometers and 3 for 711,179. In each 

 case the bulb (without enamel) was fused to the stem. Ampoules were 

 avoided in all the instruments. 



The calibration corrections Avere obtained in the usual way, a micro- 

 meter being used to measure the ends of the thread. The reduction 

 was made by the Neumann-Thiessen method. 



All readings other than those for calibration were made with a 

 telescope magnifying eighteen to twenty-four times, the eye-piece of 

 which was provided with a micrometer scale by Zeiss. With the aid 

 of this eye-piece, which serA'es to further subdivide the thermometer 

 divisions, the readings agreed to 0*005 mm. Several readings Avere 

 always taken, generally three for zero readings, six for the indications 

 in steam, twenty-one for coefficients of external pressure, fifty-four for 

 coefficients of internal pressure ; twenty-scA^en of zero and fifty-four in 

 steam for the fundamental internal correction, and ninety of comparison 

 and eighteen of zero on each instrument during the comparisons. The 



