Solitary working hours?

Hi, everyone.

Coukd you tell me what the sentence in bold means? Could you reword it to help me understand?

We hear a great deal about the tedium of machine-minding, but I think the tedium of agriculture by old-fashioned methods is at least as great. Indeed, contrary to what most philanthropists maintain, I should say that the machine age has enormously diminished the sum of boredom in the world. Among wage-earners the working hours are not solitary, while the evening hours can be given over to a variety of amusements that were impossible in an old-