228 



spending with the intervals of temperature below 100°. Joining 

 the extremities of the chords, a magnified view is obtained of the 

 curve determined from observations with temperatures uncorrected. 

 On this the author remarks, that if the temperatures required no 

 correction, the points so determined would lie in a straight line, 

 always taking for granted the integrity of the law of density and the 

 perfect accuracy of the observations. 



The next step was to perform the same computation with tem- 

 peratures corrected. The resulting values of h are given in the 

 following table : — 



Table IV. 



50° 



56°-512 

 157121 



60° 



60°-481 

 156-983 



70° 



70°-413 

 157-006 



75°. 

 75°-366 

 157-053 



80° 



80"-310 

 157-155 



90° 



90O-171 

 157-428 



1110-7 



lll°-50 



161-738 



Temp, bymerc.ther. 

 Temjk, by air-therm. 

 Values of h. 







-0-138 



-0-115 



-0-068 



-f 0-024 



+0-307 



4-617 



Diff. from h at 50°. 



The difference between h at 50° in the two tables being 1'733, a 

 straight line is drawn from the point corresponding to 100°, making 

 an angle of 17°' 33, with the chord for 50° in the uncorrected tem- 

 peratures ; and lines are drawn from the same point making angles 

 l°-38, 1°-15, 0°'68, &c. wath this line, the intersections of which 

 "with the distances or chords corresponding to the temperatures, 

 give the points which represent on the same magnified scale, the 

 observations with the temperatures corrected. The author remarks 

 that the line joining these points represents the empirical law of 

 density, and that its relation to the standard right line for the tem- 

 perature 50° is precisely what might be expected to subsist between 

 the empirical and true curve of tension. It intersects that line — and 

 intersection, not contact, is the character of empirical formulae — at 

 50°, 75°, and 100°, and at intermediate temperatures diverges from 

 it to the extent of about ^^jth of a degree at the maximum. 



Thus, he states, M. Regnault's observations between 50° and 100° 

 afford a distinct answer to the inquiry in the affirmative, and it seems 

 no longer possible to doubt that there is a difference between the 

 mercurial and air- thermometers below 100°; and that its amount 

 does not sensibly differ from the formulee that embrace MM. Dulong 

 and Petit's standard observations. He annexes these formulae in a 

 combined form ad-apted to the Centigrade scale. 



C3 D 



(1) 



temperature by air-thermometer .... log B =3*7145723 

 = temperature by mercurial thermometer A =4539°- 617 



log C3 = 6-43303 

 logD =0-78587 



