"The time will come, and that presently, when, by making use of the magnetic waves that permeate the ether which surrounds our world, we shall communicate with the Antipodes."
-Joseph Glanvill, The Vanity of Dogmatizing
That's how I first read the quote and like anything else presently that way I assumed it was true. It's usually described as the earliest prediction of the invention of radio. I've seen the quote in many texts, magazines and term papers. It first appears on the frontispiece of the book "Hello America" by César Saerchinger, first printed in 1938. It seemed believable because he was an early scientific and philosophical septic. Glanvill was a writer, philosopher, clergyman and early proponent of the scientific method. So the quote seems like something he would have written. It was the right time, the right place and he was the right man. Nonetheless, it appears we have all been pranked.
Famous as this quote is, it does not appear in his 1661 text The Vanity of Dogmatizing, nor it's 2nd revision Scepsis Scientifica. I have found a number of newspapers including the Florence Times, the Tuscaloosa News and the Register herald which all ran the same 1941 article titled "Amazing Prophesy" that probably propagated this myth. Harpers Magazine ran the same quote in an article that year as well. It's hard to say which was quoting which, but clearly no one bothered to check the source material. I even checked his other works including Sadducismus Trimphatus, Witches and Apparitions and Philosophia Pia. Inexplicably, it's just not there.You can see for yourself here or here.
I don't dismiss it entirely yet, but at the very least those lines either don't originate with Glanvill or at least not within that text. He does use the word magnetic a couple times but spelled "magnetick" as would have been common in that era. Likewise he writes "ether" as "Æther" and other similar archaic spellings. But I did find one quote possibly related which which the myth is derived.
"Now those, that judge by the narrowness of former principles and successes, will smile at these paradoxical expectations: but questionless those great inventions, that have in these later ages altered the face of all things; in their naked proposals, and mere suppositions, were to former times as ridiculous... That men should speak after their tongues were ashes, or communicate with each other in different hemisphears, before the invention of letters; could not have been thought a fiction. Antiquity would not have believed the force of our cannons; and would as coldly entertain'd the wonders of the telescope. In these we all condemn antique incredulity; and 'tis likely posterity will have as much cause to pity ours."
Glanvill's words (if they are his) didn't come true until 1932 with the debut of the BBC Empire service. [Antipodes is a now arcane term meaning two points on the Earth's surface which are diametrically opposed.] Maybe it was just that it appeals to our sense of wonder, and our profound belief in unrelenting technological progress. But the joke appears to be on us, courtesy of César Saerchinger, some 74 years ago. Congratulations.