APPENDIX. 

 CONSTANTS. -Continued. 



Weight in grammes. 

 62° F. 4° C. 



16.3479 16.3662 



0.9976 0.9987 



Astronomical Constants (Harkness). 

 Sidereal year = 365.256 357 8 mean solar days. 

 Sidereal day = 23A 56»« 4.JI00 mean solar time. 

 Mean solar day = 24A yn 56-1546 sidereal time. 

 Mean distance of the earth from the sun = 92 800 000 miles. 



Physical Constants. 

 Velocity of light (Harkness) = 186337 miles per second = 299878 km. per second. 

 Velocity of sound through dry air = 1090 n/i + 0.00367 t° C. feet per second. 

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



Weight in grains. 

 Volume. 62° F. 4° C. 



I cubic inch (determination of 1890) 252.286 252.568 

 I cubic centimetre (1890) J5-3953 ^SA^-S 



I cubic foot (1890) at 62° F. 62.2786 lbs. 



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

 height is 760 mm. and temperature 0° 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 o.ooi 29305 gramme. 

 Density of mercury at 0° C. (compared with water of ma.\imum density under atmos- 

 pheric pressure) = 13.5956. 

 Freezing point of mercury = — 38.°5 C. (Regnault, 1862.) 



Coefficient of expansion of air (at const, pressure of yOo""") for 1° C. (do.) : 0.003670. 

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



A = Aq (i — 0.000 iSi 792 / — 0.000000000 175 i" — .000000000035 116 i^). 

 Coefficient of linear expansion of brass for 1° C, /3 = 0.0000174 to 0.0000190. 

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



Ordinary glass (Recknagel) : at lo"^ C, y = 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, Regnault). 

 at constant volume, JiTv = 0.1689. 

 Ratio of the two specific heats of air (Rontgen) : A> /JiTv = i.4053- 

 Thermal conductivity of air (Graetz) : k = 0.0000484 (i + o.ooi 85 t°, C) ^""^^' 



[The quantity of heat that passes in unit time tlirough unit area of a plate of unit thickness, 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 ^° ^• 



Absolute zero of temperature (Thomson, Heat, Encyc. Brit.) : — ij-^Po C. = — 459-°4 ■^• 



Mechanical equivalent of heat :* 



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

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



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

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



Smithsonian Tables. 



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



172 



