Calibration of Mercurial Thermometers. 



181 



Lussac's method was used purely as a step-by-step method, 

 and not as a principal-point one (see the Report referred to 

 above). 



The following table contains the maximum difference ob- 

 served at any point when a pair of calibration-curves are 

 compared : — 



Instrument. 



With len9. 



With 

 Brown's instr. 



Variation 



of the 



two mean curves. 



550S0 



55081 \ 



i 



1 

 I 



55083 - 



55084 

 56117 



f 



56916 \ 



{ 



62839 

 63616 



millim. 



A and B=0 24 

 A and 0=040 

 A and D=0"29 

 B and C=0-35 

 B and D =018 

 and D=0-21 



A and B=018 

 A and 0=0-27 

 B and 0=0-12 



A and B=049 



A and B=040 

 A and 0=0-23 

 A and D = 20 

 B and 0=0-44 

 B and D=0'51 

 C and D = 0-42 



0-29 



millim. 

 A and B=0 18 



}.AandB=0-096 



1 

 J 



iAandB = 019 



AandB=0-17 

 A and B =0 096 



lAandB=0-19 



A and B=009 

 AandB=011 



0-14 



millim. 



0126 



0114 

 0156 

 0108 



0-126 



It will be seen that when a lens only is employed the 

 average maximum divergence is 0*29 millim.* ; while the 

 substitution of Brown's instrument for the lens reduces the 

 error to one half of this amount, 0'14 millim. This average 

 maximum difference corresponds very nearly indeed to that 

 observed by the Committee in the two Gay- Lussac's curves 

 which they obtained, the quantity there being 0*157 millim. f 



* Omitting calibration B of thermometer 56916, this average is 

 reduced to 0-252 millim. 



t This number is taken from the curves given in the Report (plate i. 

 fig. 1), and is somewhat higher than that given in the text (p. 16), where 

 it is stated that the " two curves nowhere differ by more than - 12 millim., 

 except at the point 135° ;" whereas it would appear, from a study of the 

 curves themselves, that there is a difference of 0-145 millim. at and near 

 123°, the difference at 135° amounting to 0'157 millim., as given above. 

 I have taken this maximum difference, inasmuch as the differences craoted 

 in the above table were measured in the same manner. 



Phil Mag. S. 5. Vol 21. No. 130. March 1886. 



