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What are the causes which have produced these great changes 

 in temperature 1 To this question there have been various 

 answers. All of them seem inadequate. The most recent 

 discoveries in astronomy and physics seem to offer some clue to 

 the solution of the problem. Herschel discovered, from apparent 

 changes in the position of the fixed stars, that the sun, with all 

 its attendant planets and satellites, was steadily moving in a 

 given direction in space. Argelander, of Bonn, M. Altho 

 Struve, of Pulkova, in Russia, and his associate, Peters, have 

 further investigated this wonderful discovery, and have deter- 

 mined that our sun is at present moving in the direction of 

 the constellation Herculus, with a speed of thirty-three million 

 miles in a year. They have further determined, that the 

 star Alcyone, one of the Pleiades, is the central star round 

 which our system is moving. This star is so distant that 

 the light by which we see it has been five hundred and 

 thirty-seven years on its journey. The nature of heat, 

 and its relation to mechanical motion, has been investigated by 

 many experimenters. Count Pumford, Mr. Joule, of Man- 

 chester, Dr. Mayer, of Heilbron, in Germany, Professor 

 Tyndal, and Sir "William Thomson, have all contributed to 

 prove that heat is molecular motion among the particles of a 

 body ; that arrested sensible motion becomes converted into 

 heat, and that heat is convertible into equivalent sensible 

 motion. The mechanical equivalent of heat has been deter- 

 mined, and with the data thus supplied, it has been calculated 

 that the stoppage of the earth iu its orbit would produce an 

 amount of heat equal to the combustion of fourteen globes of coal, 

 each equal to the earth in magnitude ; its subsequent fall into 

 the sun would generate an amount of heat equal to the com- 

 bustion of 5,600 worlds of solid carbon. The investigations 

 arising out of the discovery of Fraunhofer's lines in the solar 

 spectrum have shewn that the substance of the sun is identical 

 with that of the earth, and that if it do not receive new 

 accessions of heat it must become cooled. Sir William 

 Thomson (our respected Chairman's brother) believes that 

 the fall of meteors into the sun is the source whence the 

 sun derives new accessions of heat ; that the zodiacal light 



