162 PROCEEDINGS OF THE AMERICAN ACADEMY 



using a variety of methods, I have obtained slightly more concordant 

 results with the proposed method than with Neumann's or Pickering's, 

 all three possessing, however, nearly the same degree of precision, 

 and decidedly better results with these than with any of the other 

 existing simple methods. 



Considerable aid in eliminating errors of parallax in such work is 

 sometimes found by looking down upon the horizontal thermomet(?r 

 through a vertical tube having a small hole at each end. One of the 

 cheap French microscopes with its lenses removed, and inverted in its 

 stand, answers this purpose well. With such a device two calibrations 

 of the above described thermometer with threads of 3 cm. and 5 cm. 

 respectively, each with only one series of observations, and requiring 

 not more than one hour and a half each for completion, gave results 

 whose average difference from each other at nine points was 0.04 mm., 

 and the arithmetical sum of the extreme differences was 0.12 mm., 

 a result of sufficient accuracy for any class of work of which such an 

 instrument is capable. 



For brief descriptions of methods of separating threads of mercury 

 for calibration, reference may be made to the paper by Russell and 

 the text-book by Pickering noted below. These processes are in 

 general use, and are safe and convenient. 



Massachusetts Institute of Technology, 

 Boston, Feb. 1st, 1882. 



References upon Calibration op Closed Thermometer 



Tubes. 



Bessel. Pogg, Ann., vi. 287 (1826). 

 Rudberg. " " ix. 535, 5GG. 



« " xxxvii. 376 (1836). 



" " xl. 39, 562 (1837). 



KoHLRAUSCH. Physical measurements, p. 59 [Engl. Transl.]. 

 Pickering. Physical Manipulation, ii. 75 (1876). 

 Thiesen. " (Neumann's Method.) Carl's Rep., xv. 285 (1879). 

 Russell. ( " " ) [Transl. from Thiesen]. 



Amer. Jour. Sci., xxi. 373 (1881). 

 Marek. Carl's Repertorium, xv. 300 (1879). 



[Solution by least squares.] 

 Von Oettingen. Inaug. Diss. (Dorpat, 1865). 



[This I have been unable to obtain. S.W.H.] 



