Advertising has flourished under these new conditions. It has multiplied in volume, in prestige and respect. The perils have increased many fold. Just because the gamble has become a science, the speculation a very conservative business.
Source: Scientific Advertising by Claude C. Hopkins
He is saying that the volume and respect of advertising has increased, and the gamble has become a science. But I do not understand the last part of that sentence or perils have increased many fold.