Earlier I used my startup www.mobntotate.com to link Adam Smith's Wealth of Nation to Karl Marx's Communist Manifesto. Mobnotate is able to find ~10 places where the two authors talk about the same topic. You can see the complete list and download the Wealth of the Nation with Marx's comments here.
Here are some of the more interesting parts. Adam Smith's is a supporter of division of labor and the increase investment in machinery as a way of increasing productivity.
"The increase in the wages of labour necessarily increases the price of many commodities, by increasing that part of it which resolves itself into wages, and so far tends to diminish their consumption both at home and abroad. The same cause, however, which raises the wages of labour, the increase of stock, tends to increase its productive powers, and to make a smaller quantity of labour produce a greater quantity of work. The owner of the stock which employs a great number of labourers, necessarily endeavours, for his own advantage, to make such a proper division and distribution of employment that they may be enabled to produce the greatest quantity of work possible. For the same reason, he endeavours to supply them with the best machinery which either he or they can think of. What takes place among the labourers in a particular workhouse takes place, for the same reason, among those of a great society. The greater their number, the more they naturally divide themselves into different classes and subdivisions of employment. More heads are occupied in inventing the most proper machinery for executing the work of each, and it is, therefore, more likely to be invented. There are many commodities, therefore, which, in consequence of these improvements, come to be produced by so much less labour than before that the increase of its price is more than compensated by the diminution of its quantity." (Chapter 8 - Of The Wages Of Labour)
Marx on the other hand feel that the increase use of machine means that the relative value of labor decreases. Therefore it hurts the power of workers to the point of making them almost irrelevant.
"Owing to the extensive use of machinery, and to the division of labor, the work of the proletarians has lost all individual character, and, consequently, all charm for the workman. He becomes an appendage of the machine, and it is only the most simple, most monotonous, and most easily acquired knack, that is required of him. Hence, the cost of production of a workman is restricted, almost entirely, to the means of subsistence that he requires for maintenance, and for the propagation of his race. But the price of a commodity, and therefore also of labor, is equal to its cost of production. In proportion, therefore, as the repulsiveness of the work increases, the wage decreases. What is more, in proportion as the use of machinery and division of labor increases, in the same proportion the burden of toil also increases, whether by prolongation of the working hours, by the increase of the work exacted in a given time, or by increased speed of machinery, etc." (Manifesto Of The Communist Party: Chapter 1 - Bourgeois And Proletarians)
Smith though thinks that the cost of labour should go up and not down, despite the fact that less labour is needed.
"It is the natural effect of improvement, however, to diminish gradually the real price of almost all manufactures. That of the manufacturing workmanship diminishes, perhaps, in all of them without exception. In consequence of better machinery, of greater dexterity, and of a more proper division and distribution of work, all of which are the natural effects of improvement, a much smaller quantity of labour becomes requisite for executing any particular piece of work, and though, in consequence of the flourishing circumstances of the society, the real price of labour should rise very considerably, yet the great diminution of the quantity will generally much more than compensate the greatest rise which can happen in the price." (6. Third Sort)
