[ 180 ] 



XXVII. Notes on the Calibration and Standardizing of Mercu- 

 rial Thermometers. By Spencek Umfreville Pickering, 

 M.A., Professor of Chemistry at Bedford College *. 



HAVING had occasion to calibrate a considerable number 

 of delicate mercurial thermometers, a short notice of 

 the general results, in their bearing on the accuracy attainable 

 in calibration, may not be without interest to those who may 

 have occasion to study this question. 



Although several slightly more accurate methods of cali- 

 bration exist, Gay-Lussac's step-by -step method will no doubt 

 be the one generally employed, owing to its simplicity and 

 the comparative shortness of the calculations involved by it. 

 It is the method which is recommended in a Report made to 

 the British Association (1882) by a Committee, consisting of 

 Professors Balfour Stewart, Pucker, and Thorpe, appointed 

 for the purpose of investigating the several methods existing. 

 This method, which is the one which the author has in- 

 variably adopted, will alone be referred to in the present 

 communication . 



The instruments calibrated were all made by Casella, and 

 were etched with arbitrary scales, each division in the first 

 six instruments mentioned being 1*2 millim., and in the 

 remaining two, 1 millim. The other details respecting their 

 construction are as follows : — 



Instrument. 



Range. 



» 

 Weight of 

 mercury in bulb. 



Length 

 of scale. 





°0. 



grams. 



centim. 



55080 



10-25 



13-6 



47 



55081 



10-25 



13-5 



47 



55083 



1-16 



14-3 



46 



55084 



0-27 



143 



45 



56117 



-5-102 





52 



56916 



5-21 



15-4 



50 



62839 



x-(x+3S) 



36-2 



57 



63616 



*-(>+3-8) 



305 



60 



The average length of the scales, bei/i| thus about 51 centim., 

 is somewhat greater than that of the instrument studied by 

 the above-mentioned Committee, the length of which was 

 49 centim. 



On these thermometers twenty-seven calibrations were 

 performed, sixteen with the aid of the calibrating instrument 

 devised by F. D. Brown (Phil. Mag. [5] xiv. p. 59), and the 

 remaining eleven with a lens only. In every case Gay- 



* Communicated by the Author. 



