"As the circle of light expands, so does its circumference – the frontier between the light of knowledge and the darkness of the unknown."

I recently came across the quote in the title of this blog entry in an article dated January 7, 2021 by Kermit Pattison in BBC Science Focus Magazine entitled "Lucy and Ardi: The two fossils that changed human history." In the article the prefatory comment to the above quote is stated here in its entirety:

"New discoveries present us with a paradox: the more we learn, the more we confront what we don’t know. More than two centuries ago, the pioneering British chemist Joseph Priestley offered a wonderful metaphor for scientific progress: as the circle of light expands, so does its circumference – the frontier between the light of knowledge and the darkness of the unknown."

I did a double take on this comment. Where have I seen this before. I wrote a blog entry five and a half years ago about a quotation of J. B. Priestley that is oftentimes also attributed to Joseph Priestely, "The More Elaborate our Means of Communication, the Less we Communicate." This J.B. Priestley quote is oftentimes referred to as Priestley's paradox. Yet, the new quote I found by Joseph Priestley is being referred to as Priestley's paradox. But, in this instance we need to concentrate on Kermit Pattison's prefatory comment, "the more we learn, the more we confront what we don't know." Or alternatively, we could state this as,"The more we learn, the less we know," which echos the original J. B. Priestley paradox. Of note, Pattison's quote of Priestley does not cite the quote's source! A quick search on Google attributes the quote to Albert Einstein. However, in checking with Mr. Pattison, he reveals that the quote comes from Joseph Priestley's 1790 book “Experiments and Observations on Different Kinds of Air.” The actual quote is here:

"No philosophical investigation can be said to be completed which leaves any thing unknown that we are prompted by it to wish we could know relating to it. But such is the necessary connexion of all things in the system of nature, that every discovery brings to our view many things of which we had no intimation before, the complete discovery of which we cannot help wishing for; and whenever these discoveries are completed, we may assure ourselves they will farther increase this kind of dissatisfaction.

The greater is the circle of light, the greater is the boundary of the darkness by which it is confined: but, notwithstanding this, the more light we get, the more thankful we ought to be; for by this means we have the greater range for satisfactory contemplation. In time, the bounds of light will be still farther extended; and from the infinity of the Divine nature and the Divine works, we may promise ourselves an endless progress in our investigation of them, a prospect truly sublime and glorious. The works of the greatest and most successful philosophers are, on this account, open to our complaints of their being imperfect."

Note that Mr. Pattison has taken the liberty of paraphrasing the original quote.