160 ANNUAL OF SCIENTIFIC DISCOVERY. 



the gas and the increased density of the atmosphere. Mrs. Foote had also 

 tried the heating effect of the sun's rays on hydrogen and oxygen, and found 

 the former to be less, the latter more, susceptible to the heating action of 

 sunlight. 



SOUECE OF THE SUN'S HEAT. 



The following is an abstract of Prof. Thompson's (of England) article, 

 published some time -since, and often referred to (see Annual of Sci. Dis., 

 1854, pp. 144-148), in which he advocates the hypothesis, "that meteors 

 falling into the sun give rise to the heat which he emits." 



All the theories that have yet been proposed to account for the heat of the 

 sun, he remarks, as well as every conceivable theory, must be one or other, 

 or a combination of the following three : 



1st. That the sun is a heating body, losing heat. 



2d. That the heat emitted from the sun is due to chemical action among 

 materials originally belonging to his mass, or that the sun is a great fire. 



3d. That meteors falling into the sun give rise to the heat which he emits. 



It is demonstrable, that unless the sun be of matter inconceivably more 

 conductive of heat, and less volatile, than any terrestrial meteoric matter we 

 know, he would become dark in two or three minutes, or days, or years, at 

 his present rate of emission, if he had no source of energy to draw from but 

 primitive heat. 



The object of the communication is to consider the relative capabilities of 

 the second and third hypotheses to account for the phenomena. 



In the first place it is probable that there are always meteors falling to the 

 sun, since the fact of meteors coming to the earth proves the existence of such 

 bodies moving about in space. It is easy to prove that meteors falling to the 

 sun," must enter his atmosphere or strike his surface, with immensely greater 

 relative velocities, than those with which meteors falling to the earth, enter 

 the earth's atmosphere, or strike the earth's surface. Now, Joule has shown 

 that immense quantities of heat must be generated from this relative motion 

 in case of meteors falling to the earth, and it is all but certain that, in a vast 

 majority of cases, this generation of heat is so intense as to raise the body in 

 temperature gradually up to an intense white heat, and cause it to burst ulti- 

 mately into sparks in the air, and burn, if it be of metallic iron, before it 

 reaches the surface. Such effects must be experienced to an enormously 

 greater degree before reaching his surface, by meteors falling to the sun, if, as 

 is highly probable, he has a dense atmosphere. Hence, it is certain that 

 some light and heat radiating from the sun is due to meteors. 



It is estimated that the quantity of matter that would be required to strike, 

 is about a pound to the square foot every five hours. At this rate, the surface 

 would be covered to a depth of thirty feet in the year, if the density of the 

 deposit is the same as that of water. We find the source of meteors princi- 

 pally within the earth's orbit ; and we actually see them there as the " zodiacal 

 light," according to Herschel, an illuminated shower, or rather tornado of 

 stones. The inner parts of this tornado are always getting caught in the sun's 

 atmosphere, and drawn to his mass by gravitation. The outer edge of the 



