THE SUN AND SOLAR PHENOMENA. 53 



their direction being more or less oblique. When he is farthest from us, as in summer, 

 he is daily above the horizon twice as long as when he is nearest, at the winter solstice. 

 This continued action causes a powerful accumulation of heat ; and the nights being 

 short, but little of it is radiated, or given off, during his absence. But temperature is 

 affected by the direction of the sun's rays, whether vertical or oblique, their greatest force 

 being experienced when they are perpendicular to the surface ; while in proportion as they 

 are oblique, they glance off, and having to pass through a larger portion of the atmosphere, 

 a larger number are absorbed and dispersed by it. Out of ten thousand rays falling 

 upon the earth's atmosphere, 8123 arrive at a given point if they come perpendicularly, 

 7024 if the angle of direction is fifty degrees, 2831 if it is seven degrees, and only 5 if 

 the direction is horizontal. Now, in summer, the sun, being north of the equator, rises 

 to a greater elevation in the heavens ; the rays reach us in a more vertical direction ; 

 and the days being longer than the nights, more heat is absorbed than what is radiated. 

 But in winter he traverses those signs of the zodiac that are south of the equator ; and, 

 ascending to a less elevation in the heavens, the rays reach us more obliquely, and the 

 days being short, the solar action is less continuous. Hence in summer we have the 

 greatest heat though the earth is then farthest from the sun ; and in winter the greatest 

 cold when it is at the nearest point. 



The mean distance of the sun from the earth, as determined by observation of the 

 transits of Venus, is ninety-five millions of miles. This may be confidently regarded as 

 within T^th of the true distance, so that no error is involved either way greater than about 

 three hundred thousand miles. The immense magnitude of the solar body appears from 

 the fact, that it occupies so much space in the heavens, and presents such a stately aspect, 

 with so vast an interval between us. If a locomotive had been started five centuries and 

 a half ago, at the termination of the Crusades, and had been travelling incessantly at the 

 rate of twenty miles an hour, it would only now just have accomplished a space equal to 

 that which lies between the terrestrial and the solar surface. Though light comes to the 

 former from the latter in about eight minutes, a cannon ball would not perform the same 

 feat, retaining its full force, under some twelve years. That an object therefore should be 

 so splendidly visible as the sun, so far removed, and should so powerfully influence us 

 with light and heat, argues grand dimensions and wonderful energy. The direct light is 

 supposed to be equal to that of 5570 wax candles placed at the distance of one foot from 

 an object ; and so great is the power of the rays, that some of the men employed 

 in constructing the Plymouth Breakwater had their caps burnt in a diving-bell thirty 

 feet under water, owing to their sitting under the focal point of the convex glasses in 

 the upper part of the machine. The sun's diameter of 882,000 miles is equal to 

 111^ times that of the earth; and his circumference of 2,764,600 miles describes 

 a bulk nearly a million and a quarter times larger than our own globe, and above five 

 hundred times greater than the united volume of all the planetary bodies that revolve 

 around him. If his mass occupied the place of the earth, it would fill up the entire 

 orbit of the moon, and extend into space as far again as the path of that satellite. 

 The density of the solar substance is, however, far less than that of the matter of our 

 globe. If the two bodies could be weighed in a balance, the weight of the sun would 

 not preponderate in the same proportion as the bulk, but be only 354,936 times heavier. 

 This proportion is about a fourth less than that of the magnitude ; so that the same 

 extent of solar substance would be found four times lighter than the same extent of 

 terrestrial substance. 



To the naked eye the disk of the sun ordinarily presents a surface incomparably 

 brilliant and uniformly luminous. There is no spot, or wrinkle, or blemish. The perfect 

 purity of its aspect was an article of faith universally received by the ancient world. It 



