[Mr Bill]

That's where the trouble started, according to the correspondence unearthed by the article's author. Many dry plate manufacturers dreaded the idea of having a speed of their products measured by an independent, scientific method.

Hi Rafal, I'm not sure that's exactly correct. I have an older book which is a reprint of the 1907 Investigations on the Theory of the Photographic Process, by Sheppard and Mees. Apparently they were students, and had proposed to do independent study in order to get their BSc degrees. Their proposal was accepted, thus the book.

In one chapter, they gave a "historical introduction" on the "sensitometry of photographic plates." It seems the standard method of establishing speed was to find a minimum exposure where any effect on the plate could be seen. It was later set to some specific density, at least for one system.

Here's a small excerpt where H&D began to rock the boat:

In 1890 there was published by Messrs. Ferdinand Hurter and Vero C. Driffield, in the Journal of the Society of Chemical Industry, a paper entitled "Photo-chemical Investigations," in the course of which they gave for the first time a method of determining the sensitiveness of plates which depends on the measurement of a series of densities instead of a single reading.

Sheppard and Mees note that "there has been considerable doubt thrown on the fundamental experiments upon which it has been founded" and that they intend to largely repeat those experiments, with better accuracy.

Curiously, the modern speed systems have settled back on a single fixed density point being used, albeit with a specified (sort of) development contrast. If you've read Steven Benskins posts, he seems to be a fan of the "fractional-gradient speed method," which is more complicated. Stephen doesn't get much support for his viewpoint either. Just an interesting parallel.