One could understand “accelerated” in the quote above as either faster in time or larger in degree. Speculation leads to faster adjustment and smaller degrees of price changes.
One could understand “speculators” in the quote above as either investors reacting to uncertainty with a greater movement in their underlying expectations or investors arbitraging across any given underlying expected price discrepancy. The former will move the price up and down, the latter will reduce any range of prices. In economic theory, foresight typically refers to the former aspect and speculation typically refers to the latter aspect of human action. Although, admittedly, there is ambiguity in the economics literature concerning the use of the term, speculation.