i 3 o SCIENCE PROGRESS. 



I select from the whole list the results obtained by 

 Joule, 1843-78, Rowland, 1879, Miculescu, 1892, and I 

 would venture to add my own of 1888-93, as those to 

 which attention should chiefly be directed, because these 

 authors have (especially in the case of Rowland) given the 

 data for their thermometry. True, that Joule appears to 

 have paid little attention (comparatively speaking) to this 

 matter, but, as will be shown later, we are to some extent 

 able to repair this omission. 



Rowland devoted a great portion of his paper to the 

 description of the comparisons of his mercury and air 

 thermometers. On page 498 of my own paper I have, 

 however, given my reasons for the following statement : 

 "A study of Rowland's tables xi. to xv. leads to the 

 conclusion that the discrepancy between individual ob- 

 servations, due to the above-mentioned causes, in some 

 cases amounted to as much as '03° to '64° C. . . . and 

 appears to justify the conclusion that the value of Row- 

 land's temperature range 14 to 25° C. may be in error 

 by as much as 0*020° C," that is, over the above range, 

 an error of 1 in 550. 



Fortunately, the thermometers used by Joule are still 

 in existence, and the magnitude of the errors arising from 

 imperfections in his thermometric standards has been ap- 

 proximately ascertained; for Joule himself in 1879 made a 

 careful comparison of his thermometer with one which had 

 been standardised by Rowland, the outcome being to raise 

 Joule's final results from 772*55 to 77675 ft. lbs. (F.) in 

 latitude of Greenwich, whereas if we apply the thermometric 

 correction to all his published, instead of his final, results 

 the corrected mean becomes 779*15. 



Even in this case, however, we have not sufficient 

 data to apply the correction with accuracy, for no record 

 has been found, beyond the published numbers, of the 

 conditions under which the comparison between the ther- 

 mometers was made, although I understand from Professor 

 Schuster (in whose possession the Joule thermometers now 

 are) that search has been made for such records. Again, 

 it must be remembered that the application of the above 



