Next month's Godwit Days will bring birdwatchers to Humboldt Bay from all over, complete with their binoculars, telescopes and cameras with telephoto lenses. All these devices employ essentially the same system of optics to make distant objects seem closer, a system that dates back about 400 years.

Most reference books give the date for the invention of the telescope as 1608, and it's usually attributed to Hans Lipperhey of Middleburg, in the province of Zeeland, Holland. Two years later, a hitherto unknown professor of mathematics in Padua, Italy, published a book outlining the discoveries he'd made while observing the night sky through his homemade telescope. Galileo Galilei became an instant celeb, his book Siderius Nuncius (The Starry Messenger) was a bestseller, and the modern science of astronomy was born.

The mystery is this: Why was there a gap of over 300 years between the invention of spectacles and the invention of the telescope? After all, a telescope, in its simplest form as used (and improved) by Galileo is simply two spectacle lenses, one to correct near vision and one to correct far vision, held a few inches apart. You can easily make a telescope for yourself with a pair of distance (concave) glasses and a pair of reading (convex) glasses. Hold the reading glasses at arm's length (your objective lens) while looking at them through the distance glasses (your eyepiece). Congratulations -- you've just created a telescope!

We know that convex spectacles to compensate for presbyopia (farsightedness) were invented at the end of the 13th century. Presbyopia affects most of us at some point in our lives, as the cilia muscles of our eyes weaken to where we can no longer focus on something close -- a book, for instance. The invention of spectacles for reading must have been an incredible boon back then, especially for aging monks engaged in the painstaking work of copying manuscripts, before the invention of printing. Concave spectacles, to correct myopia (nearsightedness), were invented a little later.

We now think that two factors were responsible for the long gap between spectacles and the telescope: the poor quality of the glass then available, and the inaccuracy of the finished lenses after grinding. In fact, some historians of science believe that the idea of the telescope, in the form of two lenses -- concave and convex -- was known decades before 1608, but that it was only then, in Holland, that state-of-the-art glassmaking allowed the creation of a useful instrument. As with all inventions, theory had to be accompanied by practical technology to turn a great idea into a useful device.

Barry Evans (barryevans9@yahoo.com) is a recovering civil engineer living in beautiful Old Town Eureka. His book "Everyday Wonders: Encounters with the Astonishing World around Us" led to a four-year stint as a science commentator on National Public Radio.