[M2.18backL]                                                          [M2.18back]									18
                                                                      
[diagrams]                                                            		increased when they become large;  The reader will at once
                                                                      		understand this differentiation of strength in the masses,
                                                                      		by considering that a small stone may project from over a
                                                                      		wall as at a 1 opposite, without smallest chance of the portions
                                                                      		a a breaking off. but a great rock cannot overhang in
                                                                      		the same proportion, as at 2,without considerable danger
                                                                      		of portions of the overhanging mass giving way:  much
                                                                      		more if superincumbent weight be added;  whose pressure
                                                                      		shall be confined to the overhanging portion;  Now not only does this
                                                                      		principle applies directly to the capitals of shafts, even
                                                                      		when they are considered as crowning masses without any
                                                                      		superimposed weight, so that for instance the capital b of
                                                                      		the shaft 3, might with perfect safety project ½ a foot
                                                                      		if the shaft were only a foot in diameter and five feet
                                                                      		high but might not with safety project six feet from a
                                                                      		shaft 12 feet in diameter and sixty feet high;  But the
                                                                      		diminution of security is, in [?] still greater, when the increase of superincum
                                                                      		-bent weight is considered, and not
                                                                      		only its increase;  but its less perfect diffusion;
                                                                      		for when the capital is small, in all probability the
                                                                      		weights will be laid on it as at c or c2 and the lines of
                                                                      		pressure thrown through it to the shaft, but if the
                                                                      		capital be very large the weight will in all probability
                                                                      		be thrown on it as at d, or d2, and some of the
                                                                      		lines of resistance

[Version 0.05: May 2008]