...when tools for measuring increase their precision by orders of magnitude, new paradigms often energy, because the new found accuracy reveals anomalies that had gone undetected. One of the crucial benefits of increasing the accuracy of scales is that it suddenly became possible to measure things that had almost no weight.The discovery of 'airs' or gases at that time rests on the fact that if you heat certain substances, they lose a very small amount of its weight because they release something (a gas) into the air. The fact of this weight change was only measurable on a very sensitive scale, as the weight lost is relatively small. But the fact of this weight change was the evidence of the existence of this gas, which is not visible to the eye.
As to why Priestley, Johnson tries to dispell the myth of scientific eureka moments and to put in its place the notion of long development:
What's interesting about Priestley is not that he had a hunch, but rather that he had the intelligence and the leisure time to let that hunch lurk in the background for theirty years, growing and evolving and connecting with each new milestone in Priestley's career. We know that epiphanies are a myth of popular science, that ideas don't just fall out of the sky, or leap out of our subconscious. But we don't yet recognize how slow in developing most good ideas are, how they often need to remain dormant as intuitive hunches for decades before they flower. Chance favors the prepared mind, and Priestely had been preparing for thirty years. We talk about great ideas using the language of flashes and instant reveleation, but most great ideas happen on the scale of generations, not seconds.This becomes another moment for a disquisition by Johnson on the spreading of ideas through networks, which is a veritable obsession with him. He sees them everywhere but I am sure that he would argue, that's because they are everywhere, and I would be inclined to agree with him. He continues to develop the idea he introduced in the first chapter about the coffee houses of the era being much like the internet of the present - a forum for connection. But in this chapter he talks about the connection of the inventor to the network of ideas and associations that are peculiarly his:
...the inventor networks with his own past selves, his or her ability to keep old ideas association alive in the mind. If great ideas usually arrive in fragments, a partial cluster of neurons, then part of the secret to having great ideas lies in creating a working environment where those fragments are nurtured and sustained over time.Networking with your own past selves - as though each of our thoughts and experiences begin as separate skeins that reach back in time, but are finally woven together into cloth. I thought too how those would not be only intellectual skeins, but also purely sensoral ones (things we see, hear, or smell over time), as well as elements of emotion and personality. Lovely thought, Mr. Johnson. It seems similar to what you have done in this book - weaving what might be seen as wildly divergent strands into whole cloth both useful and beautiful.