LESSONS IN GEOLOGY. 317 



disturb the magnetic conditions of the earth, and possibly its 

 climatic conditions as well. 



The gaseous envelopes of the sun are subject to violent dis- 

 turbances or storms, consisting largely of upward and down- 

 ward movements of the gases. It is thought by some that the 

 sun spots are in some way the result of these storms. The quan- 

 tity and intensity of the heat of the sun is beyond comprehension 

 and yet it must be diminishing as there seems to be no adequate 

 means of supplying the enormous and continuous loss of heat by 

 radiation. Others claim that while the sun is continuously send 

 ing out immense quantities of heat, it is actually increasing in 

 temperature through condensation of material due to gravity. 

 The sun is spherical in form and rotates once in about 25 or 26 

 days. Besides rotation, the sun with the whole solar system 

 has a progressive motion in space toward the constellation of 

 Hercules. Its diameter cannot be determined with accuracy, but 

 is given as about 866,000 miles. 



The Planets are spherical bodies which revolve around the sun 

 from west to east in elliptical orbits. Named in their order from 

 the sun the planets are Mercury, Venus, Earth, Mars, Jupiter, 

 Saturn, Uranus and Neptune. Venus, Jupiter, Mars and Saturn 

 appear as brilliant stars. The planets differ in size, time of rev- 

 olution and in density. Mercury is more dense than the earth, 

 but the sun and all the other planets are less dense! Venus seems 

 to have an 'atmosphere, but Mercury is not known to have one. 

 No permanent marks or features have ever been discovered on 

 these planets so that it is not certainly known whether they ro- 

 tate or not. Mars and the earth each has a solid crust, and 

 somewhat similar atmospheric conditions and each rotates from 

 west to east. Jupiter and Saturn seem to be masses of molten 

 matter, each surrounded by a deep dense atmosphere, in which 

 extensive changes and disturbances are known to occur, and 

 somewhat permanent markings can be seen, from which it ap- 

 pears that each of these planets rotates from west to east. But 

 little is known of Uranus or Neptune beyond some idea of their 

 size, density and time of revolution. 



