No. XXIII.] APPENDIX. 319 



lead or glass are brought into contact they mutually adhere, and some- 

 times greatly to the manufacturer's discomfort. 



Liquids and solids in contact have a power of mutual attraction, as in 

 capillary attraction. 



Gases and liquids have also this power of attraction, as in the case of 

 muriatic acid gas and water. 



I will now show you a very beautiful experiment, proving that attrac- 

 tion is existent between gases and solids. Some years ago I discovered 

 that coke or charcoal might have so much hydrogen firmly attracted to it, 

 that when plunged into solutions of gold, silver, or copper, an extensive 

 deposition of metal takes place, and I have found that it would retain the 

 gas for many days. 



Attraction is also exerted between gaseous bodies, according to the 

 law of diffusion so elegantly developed by Graham ; and even carbonic acid 

 (a very heavy gas) passes into the atmospheric air. 



Lastly, liquids attract each other by a law very similar to that of the 

 diffusion of gases. 



Hitherto we have considered the attraction of particles of matter in 

 indefinite quantities, or of the attraction of masses already aggregated ; 

 but particles of two or more different kinds of matter may be attracted to 

 produce a totally new substance, having none of the properties of former 

 particles: thus chlorine and sodium form common salt; oxygen and 

 hydrogen, water. 



Attracted matter, either in masses or in the most attenuated particles, 

 attracts other masses at any distance, and by this power of gravity every- 

 thing in the universe is kept in position ; to this power the sun, the moon, 

 the earth, the stars in the firmament, and every substance in the world, 

 owes its position. 



In the cases of attraction already described the power appears to be 

 exercised promiscuously, but there are cases in which attraction is exerted 

 in definite directions. Crystals are masses of attracted matter of this 

 character, as their particles are attracted unequally in different directions. 

 In consequence of this they yield to mechanical force in some directions, 

 not in others; they expand unequally by heat, they are acted upon 

 unequally by magnetism, and they have very curious properties in relation 

 to light. Not only in crystalline bodies do we observe that attraction is 

 exercised in a definite direction, but we observe a direction in the power 

 of attraction during the magnetic state. A bar of iron, when it suddenly 

 assumes this state, appears to have its former attractions altered, for under 

 favourable circumstances it will sound a distinct musical note. When a 

 magnetic body attracts another body capable of assuming the magnetic 

 state, the second substance also evinces a similar direction in the exercise 

 of the power of attraction. From these views we deduce that the idea of 

 magnetism is derived from certain kinds of matter, under certain circum- 

 stances, evincing the power of attraction in a definite direction. 



We have considered the mode in which attraction acts to unite 

 particles of matter, and thus construct the various objects of which the 

 material universe is composed. Now let us pause to consider the earth at 

 rest. The quiet which gives the loveliness to evening, and soothes the 

 mind after the business of the day, forms but a dim shadow of that awful 

 quiet which would exist were attracted matter not capable of being acted 



