§ 6. One further point emerges from the evidence relating to efficiency and high wages. According to Schulze-Gaevernitz's formula, every fall in piece wages is attended by a rise in weekly wages. But it should be kept in mind that a rise in time wages does not necessarily mean that the price of labour measured in terms of effort has been raised. Intenser labour undergone for a shorter time may obtain a higher money wage per unit of time, but the price per unit of effort may be lower. It has been recognised that a general tendency of the later evolution of machinery has been to compress and intensify labour. In certain classes of textile labour the amount of muscular or manual labour given out in a day is larger than formerly. This is the case with the work of children employed as piecers. In Ure's day (1830) he was able to claim that during three-fourths of the time spent by children in the factory they had nothing to do. The increased quantity of spindles and the increased speed have made their labour more continuous. The same is true of the mule spinners, whose labour, even within the last few years, has been intensified by increased size of the mule. Though as a rule machinery tends to take over the heavier forms of muscular work, it also tends to multiply the minor calls upon the muscles, until the total strain is not much less than before. What relief is obtained from muscular effort is compensated by a growing strain upon the nerves and upon the attention. Moreover, as the machinery grows more complex, numerous, and costly, the responsibility of the machine-tender is increased. To some considerable extent the new effort imposed upon the worker is of a more refined order than the heavy muscular work it has replaced. But its tax upon the physique is an ever-growing one. "A hand-loom weaver can work thirteen hours a day, but to get a six-loom weaver to work thirteen hours is a physical impossibility."[235] The complexity of modern machinery and the superhuman celerity of which it is capable suggest continually an increased compression of human labour, an increased output of effort per unit of time. This has been rendered possible by acquired skill and improved physique ensuing on a higher standard of living. But it is evident that, where it appears that each rise in the standard of living and each shortening of the working-day has been accompanied by a severer strain either upon muscles, nerves, or mental energy during the shorter working day, we are not entitled to regard the higher wages and shorter hours as clear gain for the worker. Some limits are necessarily imposed upon this compressibility of working effort. It would clearly be impossible by a number of rapid reductions of the working day and increases of time wages to force the effectiveness of an hour's labour beyond a certain limit for the workers. Human nature must place limits upon the compression. Though it may be better for a