26 SCIENTIFIC AGRICULTURE. 



almost inconceivable. And still this gas is material, and must 

 be made up of an aggregate of particles. A single grain of 

 gold used in gilding silver wire, is made to cover a surface of 

 1400 square inches, and still the gold upon the millionth of a 

 square inch when examined by the microscope, is distinctly 

 visible. A square inch of gold leaf may be divided into one 

 billion and four hundred millions of particles, and still retain 

 all the characters and color of a large mass. 



Chemical action may be supposed to carry the process of 

 division to a much higher attenuation than mechanical means. 

 A single drop of solution of indigo colors 1000 cubic inches of 

 water, and yet this coloring matter is an aggregate of distinct 

 particles. The fineness of particles has an important effect 

 on the chemical action of one body upon another. Perhaps a 

 more definite idea may be given by the following example. 

 The author had the pleasure of examining with Professor 

 Dewey's improved microscope, some fossil infusoria, which 

 were so small that they appeared like perfectly impalpable 

 powder, and not the least gritty between the teeth. These 

 minute particles of dust when subject to the greatest magni- 

 fying power of the instrument, proved to be the shells of in- 

 fusoria resembling in shape the sow-lug and trilobite, and ap- 

 parently from three to four inches in length and one inch in 

 width. And still, minute as they were, they must have had 

 when living, all the organs and machinery of animals of large 

 size. 



GRAVITY. 



The term gravity, in natural philosophy, signifies weight : it 

 is that force or attraction in nature which causes all bodies to 

 move towards the earth when not prevented by some other 

 force. The gravitating force of a body is in proportion to the 

 quantity of matter which it contains. The force of gravity in- 

 creases in falling bodies, in proportion as they approach the 

 earth. Bodies of the same bulk, do not always possess the 



