RECENT PROGRESS OF NATURAL SCIENCE. 599 



ture. This new doctrine appears in the mechanical theory of heat an- 

 nounced by Joule, Kronig, Maxwell, and Clausius, in the doctrine of 

 the conservation of energy of Ileltnholtz and Thomson, and by means 

 of the brilliant writings of Tyndall it has become the common property 

 of the educated world. Electricity and magnetism, heat and light, 

 muscular energy and chemical attraction, motion, and mechanical work 

 all forces in the universe are only different forms of one and the 

 same power, which has dwelt from the first in matter in invariable 

 quantity, neither increased nor diminished ; not the least trifle of it 

 can be annihilated or created. Only the phenomenal forms of power 

 are changeable ; light can be converted into a chemical equivalent, 

 this again into heat, heat into motion, and indeed a fixed quantity of 

 one force always and only into an equivalent quantity of another. In 

 like manner also the quantity of matter has remained unchanged from 

 the beginning ; not the least particle or molecule can be annihilated 

 or ci'eated out of nothing, and only in the transformation of perishable 

 bodies are the molecules formed into ever-new combinations. What 

 we distinguish as natural forces are only movements of molecules, for 

 the least particles of matter out of which bodies are comj^osed are not 

 inseparably united to each other, but are loosely held together and in 

 continuous whirling and undulatory motion ; according to the swift- 

 ness and width of undulation of the molecule will this motion of our 

 nerves be ^regarded, now as sound, now as heat, then as light or as 

 color. Moreover, the chemical union of the elements of matter, the 

 attractive power of gravitation in all the bodies of the universe, are 

 but varied forms of this universal motive force. The unity and per- 

 manency of substance with its two attributes, matter and force, and 

 their innumerable modifications, which go to form the bodies of the 

 universe, were in the first instance enunciated as a philosophical 

 maxim by the great thinker Spinoza. Now it is established as a philo- 

 sophic fact by means of exact measure and weight. 



Again, on the inner organization of the system of the universe has 

 unexampled light been thrown by the wonderful researches which 

 were begun in 1859 by two men, united by the closest bonds of a 

 friendship which bore rich fruit for science. After the light of the sun 

 had, in the third decade of this century, been brought into the service 

 of art by Niepce and Daguerre, Bunsen and Kirchhoff compelled it 

 also to render service to chemistry and astronomy. Like those ma- 

 gicians of the legend who, through the power of their knowledge, 

 compelled the spirits of the elements to disclose their most recondite 

 secrets, the genius of these men compelled the rays of light imprisoned 

 in the spectrum apparatus to make revelation of tilings in the world 

 of stars which the curiosity of men had deemed forever inaccessible. 

 Already had Kirchhoff ascertained what terrestrial elements were pres- 

 ent in the sun's atmosphere, and what were not ; quite recently has it 

 been discovered that there is even present in the sun a substance 



