CONSTANTS. 



CONSTANTS. 



1402 ft. Ibs. of work or energy are required at latitude 45, sea-level (g = 980.6), to 

 i IK of water through i Out. at 15 ('. For most engineering purposes 



1400 ft. Ibs. would be near enough. 

 4.i90'io 7 ergs of work or energy are required to raise i gramme of water through i C. 



at 15 C. 



any given locality, multiply by the ratio g& : g, where (/ 4 - is 



the value (980.6) of the acceleration of gravity at latitude 45, sea-level, and g is the 

 value at the given plaee. The latter may be obtained from the latitude and altitude of 

 the plaer by the formula given upon the next page, unless otherwise better known. The 

 altitude correction is but six one-thousandths of one per cent (o.oo 006) for each 1000 ft. 

 of elevation, and therefore quite negligible. Within the limits of uncertainty of the 

 quantities involved the latitude correction for places between 30 and 60 may be 

 applied thus : 



427-3 778-8 1402 



0.04 kgm. 0.07 ft. Ibs. 0.13 ft. Ibs. 



0.04 kjrm. 0.07 ft. Ibs. 0.13 ft. Ibs. 



For each degree of latitude north of 45 subtract 

 F>r each degree of latitinl<- south of 45 add 



NOTE. The persistence with which the time-honored values, 772 ft. Ibs. and 424 kgm., of this most impor- 

 tant constant are adhered to in practice, although known to be nearly one per cent too small, is due large] v to 

 the flagrant negligence of the authors of text-books of both physics and engineering. No attention is paid to 

 the fact that Joule's original data have been amended aceejit/i/>/ f<> him. and that his work has been supple- 

 mented by the elaborate researches of at least three other independent observers with radically diverse 

 methods. How n-markably these new results check each other and confirm Joule's amended results may be 

 seen from the following table, which is given to indicate the source of the foregoing values. 



The specific heat of water, and therefore the value of ,7, diminishes slightly with rise 

 of temperature. The rate of this diminution is not yet satisfactorily determined, but 

 about as nearly as it is now known the true specific heat s t at any temperature t not far 

 from 15 C., may be expressed in terms of true specific heat s^ at 15 C. by 



s t = sis[i. -o.oo 030 (t r- 15)]. 



Hence J t , the number of kgm. or ergs necessary to raise i kgr. of water from t to 

 t? + i, will be 



J t = e/ic [i. - 0.00030 (t - 15)] [Range 13 - 20], 



CONSTANTS. 



