This a view of the complete counterweights housing. The two ropes can be seen going down to the right near the rafters.
This was the only place in the attic with enough headroom to contain the counterweights - if it had not been enough I would have had to abandon the 2:1 reduction pulleys so that the travel of the weights was halved, and the mass of the weights doubled.
This construction was used a) to provide a solid support for the weights (the load is carried by both the rafters at the top and the joists at the bottom), and b) to prevent activity in the attic obstructing the action of the weights - as seen here, this is storage space.