(_e_) _Ease or simplicity of labour involved._--Where abundance of cheap labour adequate to the work can be obtained, and particularly in trades where women and children are largely engaged, the development of machinery has been generally slower. This condition often unites with (_b_) or (_c_) to retain an industry in the "domestic" class. A large mass of essentially "irregular" work requiring a certain delicacy of manipulation, which by reason of its narrowness of scope is yet easily attained, and which makes but slight demands upon muscular force or intelligence, has remained outside machine-production. Important industries containing several processes of this nature have been slower to fall into the complete form of the factory system. The slow progress of the power-loom in cotton and wool until after 1830 is explained by these considerations. The stocking-frame held out against machinery still longer, and hand work still plays an important part in several processes of silk manufacture. Even now, in the very centre of the factory system, Bolton, the old hand-weaving is represented by a few belated survivors.[82] (_f_) _Skilled Workmanship._--High skill in manipulation or treatment of material, the element of art infused into handicraft, gives the latter an advantage over the most skilful machinery, or over such machinery as can economically be brought into competition with it. In some of the metal trades, in pottery and glass-making there are many processes which have not been able to dispense with human skill. In these manufactures, moreover, more progress is attributable to specific inventions than to the adoption of the common machinery and motor-power which are not largely available in the most important processes.