466 APPENDIX. 



and the superficial characters are often also different 

 from the real ones ; from their containing water, as I 

 formerly showed. This fact, hitherto unobserved, 

 cannot be known, unless from deep-seated specimens; 

 and hence the necessity of more powerful hammers 

 than those in use. The form therefore becomes an 

 important object ; that we may command the greatest 

 force with the least encumbrance. 



The hammer of quarrymen is a double truncated 

 wedge : while nothing but extreme ignorance of ma- 

 thematical principles could have extended this form 

 to those of road-makers and geologists : whence their 

 inefficiency, even under an inconvenient increase of 

 weight. The fragment, in each case, is produced by 

 exciting a vibration in an imaginary lamina, through 

 a motion too sudden to be accompanied by that of the 

 adjoining parts. It is forgotten that the communica- 

 tion of motion is not regulated by the momentum, 

 simply, of the moving body. The weight and the ve- 

 locity cannot be indifferently interchanged: and thence 

 strange errors in many other matters also, of daily 

 practice. But, not to enter further on this subject, 

 suffice it, that it requires a time inversely propor- 

 tioned to the tenacity of a body, to allow it to be dis- 

 placed in a mass ; whence, if additional momentum 

 be required, the weight, not the velocity, must be in- 

 creased. But if it is required to disintegrate the same 

 body, it is the velocity that must be augmented. It 

 is by impulse that the stone is broken in the present 

 case. Hence it is useless to increase the weight of 

 such a hammer, beyond that to which the hand can 

 give the greatest velocity, since there is thus a loss of 

 power. I have taken four pounds as the extreme 

 weight; while two, or less, will, in a proper form, suf- 

 fice for most rocks. 



