Karl Marx (1818–1883) and Friedrich Engels (1820–1895) are best known for their collaborative work The Communist Manifesto (1848). However, the two had been observing the real consequences of industrialization for factory workers, particularly in Manchester, England, for many years before this. Working in his father’s cotton factory in England, Engels had witnessed the inequities imposed by industrial systems, and he composed a scathing attack on these systems in his Condition of the Working-Class in England (1845). When Marx befriended Engels in Manchester, he too came to see how local conditions could lead to wide-ranging theories about labor, wages, and the measurement of “costs.” In this lecture, delivered in December 1847, Marx took his audience through the most basic elements of the philosophy that would culminate in Das Kapital (vol. 1, 1867).
http://www.marxists.org/archive/marx/works/1847/wage-labour/, first published in German in the Neue Rheinische Zeitung (April 5–8, 11, 1849), and edited and translated by Friedrich Engels for an 1891 pamphlet.
The British Parliament took on a series of initiatives to investigate the lives of women and children in the mid-nineteenth century, and the resulting testimonies, presented by workers to the various parliamentary commissions make for fascinating—and uniquely visceral—reading. The lives of working children are rarely detailed in historical sources from any era, but these testimonies had a direct impact, if not a fully humane one, on the lives of British laborers. These documents were collected for Lord Ashley’s Mines Commission of 1842, and the shocking testimony resulted in the Mines Act of 1842, which prohibited the employment in the mines of all females and of boys under 13 years of age.
http://www.victorianweb.org/history/ashley.html, from Readings in European History Since 1814, ed. Jonathan F. Scott and Alexander Baltzly (New York: Appleton-Century-Crofts, 1930), drawing on Parliamentary Papers, 1842, vols. 25–27, Appendix 1, 252, 258, 439, 461; Appendix 2, 107, 122, 205.