APPENDIX. 

 CONSTANTS.- Continued. 



Astronomical Constants (Harkness). 

 Sidereal year = 365.256357 S mean solar days. Tropical year = 365.2422 d. 



Sidereal day = 23/' 56*" 4. 100^ mean solar time. 

 Mean solar day = 24A 3'" 56.546^ sidereal time. 

 Mean distance of the earth from the sun — 92S00000 miles. 



Physical Constants. 



Velocity of light (IIarkness) ^ 1S6337 miles per second = 299878 km. per second. 

 Velocity of sound through dry air = 1090 \/i +0.00367^ C. feet per second. 

 Weight of distilled water, free from air, barometer 30 inches : 



Weight in grains. Weight in grammes. 



Volume. 62° F. 4° C. 62° F. 4° C. 



I cubic inch (determination of 1890) 252.286 252.568 16.3479 16.3662 

 I cubic centimetre (1890) 15-3953 I5-4I25 0.9976 0.9987 



I cubic foot (1S90) at 62° /^ 62.2786 lbs. 



A standard atmosphere is the pressure of a vertical column of pure mercury 

 whose height is 760 mm. and temperature o" C, under standard gravity at 

 latitude 45° and at sea level. 

 I standard atmosphere = 1033 grammes per sq. cm. = 14.7 pounds per sq. inch. 

 Pressure of mercurial column i inch high = 34.5 grammes per sq. cm. = 0.491 

 pounds per sq. inch. 

 Weight of dry air (containing 0.0004 of its weight of carbonic acid) : 



I cubic centimetre at temperature 32° F. and pressure 760 mm. and under 

 the standard value of gravity weighs 0.00129305 gramme. 

 Density of mercury at 0° C. (compared with water of maximum density under 



atmospheric pressure) = 13.5956. 

 Freezing point of mercury = — 38?5 C. (REGNAULT, 1862.) 



Coefficient of expansion of air (at const, pressure of 76o'«'«) for 1° C. (do.): 0.003670. 

 Coefficient of expansion of mercury for Centigrade temperatures (Broch) : 



[^ = /S^^(l- 0.000 iSl 792 2! -0.000 000 GOO 1 75/2 - .000000000035 116^). 



Coefficient of linear expansion of brass for 1° C, ^ = 0.0000174 to 0.0000190. 

 Coefficient of cubical expansion of glass for 1° C, 7 = 0.000021 to 0.000028. 



Ordinary glass (Recknagel) : at 10° C, 7 = 0.0000255 ; at 100°, 7 = 0.0000276. 

 Specific heat of dry air compared with an equal weight of water : 



at constant pressure, A/. = 0.2374 (from 0° to 100° C, Regnaui^t). 



at constant volume, Kv =0.1689. 



Ratio of the two specific heats of air (RonTGEn): Kp/ Kv^= i.4053- 



Thermal conductivity of air (GraETz) : k = 0.0000484 (i +0.001 85 f C.) ^^"^^ • 



[The quantity of heat that passes in unit time through unit area of a plate of unit thick- 

 ness, when its "opposite faces differ in temperature by one degree.] 



Latent heat of liquefaction of ice (BunsEn) = 80.025 mass-degrees, C. 



Latent heat of vaporization of water =: 606.5 — 0.695 /° C. 



Absolute zero of temperature (Thomson, Heat, Encyc. Brit.): —2'jf.o C. = — 459°4 -^• 



Mechanical equivalent of heat* : 



I pound-degree, F. (the British thermal unit) = about 778 foot-pounds. 

 I pound-degree, C. = 1400 foot-pounds. 



I calorie or kilogramme-degree, C. = 3087 foot-pounds = 426.8 kilogram- 

 metres = 4187 joules (for ^ = 981 cm.). 

 * Based on Prof. Rowland's determinations. (Proc. Am. Acad. Arts and Set".; 1880.) 



Smithsonian Tables. 



