AIM AND PROGHESS OP PHYSICAL SCIENCE. 381 



of heat) enables us to detect remains of this loosely- 

 distributed naatter in the nebulae ; we recognise it in the 

 meteor-showers and comets ; the act of agglomeration 

 and the development of heat still continue, though in 

 our portion of the stellar system they have ceased to 

 a great extent. The chief part of the primordial 

 energy of the matter belonging to our system is now 

 in the form of solar heat. This energy, however, will 

 not remain locked up in our system for ever : portions 

 of it are continually radiating from it, in the form of 

 light and heat, into infinite space. Of this radiation 

 our earth receives a share. It is these solar heat-rays 

 which produce on the earth's surface the winds and the 

 currents of the ocean, and lift the watery vapour from 

 the tropical seas, which, distilling over hill and plain, 

 returns as springs and rivers to the sea. The solar rays 

 impart to the plant the power to separate from carbonic 

 acid and water those combustible substances which serve 

 as food for animals, and thus, in even the varied changes 

 of organic life, the moving power is derived from the 

 infinitely vast store of the universe. 



This exalted picture of the connection existing between 

 all the processes of nature has been often presented to 

 us in recent times ; it will suffice here that I direct 

 attention to its leading features. If the task of physical 

 science be to determine laws, a step of the most com- 

 prehensive significance towards that object has here been 

 taken. 



The application of the law of the conservation of force 

 to the vital processes of animals and plants, which has 

 just been discussed, leads us in another direction in 

 which our knowledge of nature's conformity to law has 

 made an advance. The law to which we referred is 

 of the most essential importance in leading questions 

 of physiology, and it was for this reason that Dr. Mayer 



