248 PROGRESS OF SCIENCE. 



fields superposed one over another, or again the development 

 of the organic world from protoplasm to man, reveals a 

 past so remote, and during which too our present laws were 

 at work, that twenty millions of years is a mere fraction of 

 the time required to give the earth its present form and 

 life. Some would speak of no less than 680 millions of 

 years for the accomplishment of that work. Hence the 

 problem remains unsolved, but the divergence between the 

 two sets of philosophers robs neither of our admiration, for 

 the mathematical results of each, considering the premises, 

 stand among the highest achievements of modern science ; 

 the discrepancy existing between the results of geologists 

 and physicists will certainly be bridged one day, and the 

 different conclusions merged into one truth. Helmholtz, 

 like Sir W. Thomson, also directed his attention to mole- 

 cular physics, and their role in the general economy of the 

 universe, and both physicists pretty closely agree in the 

 propounding of a new hypothesis, viz., the Vortex Theory, 

 which would remove the barriers between the various 

 branches of physics. We owe also to Helmholtz a series 

 of demonstrations tending to prove, and proving, that HEAT 

 IS A MODE OF MOTION. His essay on the conservation of 

 energy is the finest composed on the subject. He traces 

 up all the transformations of energy, as presented by heat, 

 for instance, in wind, plants, animals, coals ; in sky, air, 

 and earth ; and shows its reappearance in ways as numerous 

 and unlike as it is possible to conceive. It is stored in 

 coal in its smallest compass : I Ib. being capable of lifting 

 100 Ibs. to a height of 20 miles the sun, we need scarcely 

 add, being to us on earth the one great fount from which 

 all energy is derived. Well may we admire Helmholtz, one 

 of the most brilliant and solid geniuses of our time. 



1824 87. Kirchhoff, in collaboration WITH BUNSEN, 

 invented the four-prism SPECTROSCOPE (1859), and by its 

 means opened a new mode of CHEMICAL ANALYSIS, at 

 once rapid and unerring the presence of a i8o-millionth 

 part of a grain of sodium, for instance, being detected with 

 absolute certainty. The spectroscope is an instrument for 

 separating luminous vibrations of different wave-lengths, 



