60 Mr. F. D. Brown's Notes on Thermometry. 



Two tubes were calibrated with this apparatus, and tables 

 of their volumes from the first division compiled ; they were 

 then furnished with bulbs, filled with mercury, and sealed 

 up in such a manner that they formed thermometers capable 

 of indicating temperatures between 0° and 150° C. The 

 fixed points of the two thermometers having been determined 

 with the precautions indicated below, tables showing the 

 temperatures corresponding to the readings of the scale were 

 made in the usual manner ; the two instruments were then 

 compared together, either in a large tank of water which was 

 kept well stirred, or in the steam-apparatus which I de- 

 scribed to the Physical Society at the time when these expe- 

 riments were made. Before a series of readings were taken, 

 both thermometers were heated for at least half an hour in 

 steam, while their zero-points were observed after the series 

 was completed. The numbers given in the following table 

 show that the two thermometers gave practically identical 

 readings. It would seem, therefore, that the mercurial ther- 

 mometer, when carefully made and systematically heated, does 

 really possess that valuable property of a standard, of being 

 capable of exact reproduction. 



Reading of AS, 



Eeading of BS, 



Corresponding 



Corresponding 





corrected for 



corx-ected for 



value of AS, 



value of BS, 



Difference. 



index-error. 



index-error. 



in degrees. 



in degrees. 





58-55 



70-64 



1430 



14-29 



-•01 



134-33 



150-11 



33-69 



33-71 



4-02 



179-69 



197-20 



45-29 



45-30 



+•01 



321-97 



345-96 



81-88 



81-88 



•00 



23-42 



33-74 



5-28 



5-28 



•00 



26-33 



36-83 



6-03 



604 



+ •01 



30-07 



40-63 



6-99 



6-97 



-02 



33-76 



4457 



794 



7-93 



-•01 



43-32 



54-70 



10-40 



10-40 



•00 



47-98 



59-60 



11-59 



11-59 



•00 



69-42 



82-13 



17-09 



1709 



•00 



91-61 



10552 



22-78 



22-79 



+ •01 



Determination of the Zero-jioint. 

 In most books on physics it is stated that, in order to 

 obtain the zero-point of a thermometer, the instrument should 

 be placed in a vessel filled with broken ice and provided with 

 holes at the bottom, through which the water formed by the 

 melting of the ice may escape. In order to learn whether 

 this method is the best possible, the following experiments 

 were made: — A number of tin pots, about 7 inches high and 

 4 inches in diameter, were obtained, and holes made in the 

 bottoms of two or three of them. A large block of ice was 



