206 ASTRONOMY. 



Professor Laiigley's expedition started in July, 1881, and took uj) a 

 station on Mount Whitney, in tlie Sierras, where observations were 

 made to determine the amount of solar heat received by the earth. 

 This was the main object of the expedition. Several minor researches 

 of interest were also prosecuted ; among others, an attempt was made 

 to see the sun's corona and Vulcan. It is too soon as yet to speak of 

 the results of the expedition, which have not been published. 



Statistics of the sun. — The following statistics of the sun, comprising 

 facts which can be stated in numbers, are selected from Professor 

 Young's work, "The Sun": 



Solar parallax (equatorial horizontal), 8.80" ± 0.02". 



Mean distance of the sun from the earth, 92,885,000 miles, 149,480,000 

 kilometres. 



Variation of the distance of the sun from the earth between January 

 and June, 3,100,000 miles, 4,950,000 kilometres. 



Linear value of 1" on the sun's surface, 450.3 miles, 724.7 kilometres. 



Mean angular semi-diameter of the sun, 16' 02.0" ± 1.0". 



Sun's linear diameter, 860,400 miles, 1,394,300 kilometres. (This may, 

 perhaps, be variable to the extent of several hundred miles.) 



Eatio of the sun's di ameter to the earth's, 109.3. 



Surface of the sun compared with the earth, 11,940. 



Volume, or cubic contents, of the sun compared with the earth, 

 1,305,000. 



Mass, or quantity of matter, of the sun compared with the earth, 

 330,000 ± 3,000. 



Mean density of the sun compared with the earth, 0.253. 



Mean density of the sun compared with water, 1.406. 



Force of gravity on the sun's surface compared with that on the 

 earth, 27.6. 



Distance a body would fall in one second, 444.4 feet, 135.5 meters. 



Inclination of the sun's axis to the eclij)tic, 7° 15'. 



Longitude of its ascending node, 74°. 



Date when the sun is at node, June 4-5. 



Mean time of the sun's rotation (Carrington), 25.38 days. 



Time of rotation of the sun's equator, 25 days. 



Time of rotation at latitude, 20°, 25.75 days. 



Time of rotation at latitude, 30°, 26.5 days. 



Time of rotation at latitude, 45°, 27.5 days. 



(These last four numbers are somewhat doubtful, the formulae of va- 

 rious authorities giving results differing by several hours in some cases.) 



Linear velocity of the sun's rotation at his equator, 2.261 miles per 

 second, 2.028 kilometers per second. 



Total quantity of sunlight, 6,300,000,000,000,000,000,000,000,000 can- 

 dles. 



Intensity of the sunlight at the surface of the sun, 190,000 times that 

 of a candle flame, 5,300 times that of a metal in a Bessemer converter, 

 146 times that of a calcium light, 3.4 times that of an electric arc. 



