MECHANICS. 91 



some late experiments are said to have carried it to 



nrW th P art - 



A Vacuum. 



It is well known in mechanics that a vacuum, 

 however produced, is a source of great mechanical 

 power, and it continues to be still the great principle 

 of the engines of the present day : namely, the crea- 

 tion of a vacuum under or above the piston. 



Bramah's LocKs. 



A lock of five slides admits of 3000 variations, 

 while one of eight will have no less than 1,935,360 

 changes ; or in other words, that number of attempts 

 at making a key, or at picking it, may be made before 

 it can be opened. This difficulty, great as it is, has 

 been increased an hundred fold by an improvement 

 of his sons. The security of Bramah's locks depends 

 on the doctrine of combinations, or multiplication of 

 numbers into each other, which is known to increase 

 in the most rapid proportion. 



Solid Figures. 



There can be no more than five regular solid 

 figures, terminated by plane surfaces, which are all 

 similar and equal ; viz. the tetrahedron, the cube, 

 the octahedron, the dodecahedron, and the eicosi- 

 hedron. 



Touch. 



The ultimate particles of matter never touch, 

 however solid in appearance, and no force can press 

 them into real mathematical contact. 



Elastic Bodies. 



The further the particles of elastic bodies are 

 drawn from each other until they separate, the 

 stronger they seem to attract, as Indian rubber, which 



