Historic Inventions

by Rupert Sargent Holland

“You must know then that about two months ago a report was spread here that in Flanders a spy-glass had been presented to Prince Maurice, so ingeniously constructed that it made the most distant objects appear quite near, so that a man could be seen quite plainly at a distance of two miles. This result seemed to me so extraordinary that it set me thinking, and as it appeared to me that it depended upon the laws of perspective, I reflected on the manner of constructing it, and was at length so entirely successful that I made a spy-glass which far surpasses the report of the Flanders one. As the news had reached Venice that I had made such an instrument, six days ago I was summoned before their Highnesses, the Signoria, and exhibited it to them, to the astonishment of the whole senate. Many of the nobles and senators, although of a great age, mounted more than once to the top of the highest church tower in Venice, in order to see sails and shipping that were so far off that it was two hours before they were seen, without my spy-glass, steering full sail into the harbor; for the effect of my instrument is such that it makes an object fifty miles off appear as large as if it were only five.

“Perceiving of what great utility such an instrument would prove in naval and military operations, and seeing that His Serenity the Doge desired to possess it, I resolved on the 24th inst. to go to the palace and present it as a free gift.” So Galileo did, and as a result the senate elected him to the Professorship at Padua for life, with a salary of one thousand florins yearly.

But what were Galileo’s claims to the invention of this great instrument? Here is what he wrote in 1623. “Perhaps it may be said that no great credit is due for the making of an instrument, or the solution of a problem, when one is told beforehand that the instrument exists, or that the problem is solvable. It may be said that the certitude of the existence of such a glass aided me, and that without this knowledge I would never have succeeded. To this I reply, the help which the information gave me consisted in exciting my thoughts in a particular direction, and without that, it is possible they may never have been directed that way; but that such information made the act of invention easier to me I deny, and I say more—to find the solution of a definite problem requires a greater effort of genius than to resolve one not specified; for in the latter case hazard, chance, may play the greater part, while in the former all is the work of the reasoning and intelligent mind. Thus, we are certain that the Dutchman, the first inventor of the telescope, was a simple spectacle-maker, who, handling by chance different forms of glasses, looked, also by chance, through two of them, one convex and the other concave, held at different distances from the eye; saw and noted the unexpected result; and thus found the instrument. On the other hand, I, on the simple information of the effect obtained, discovered the same instrument, not by chance, but by the way of pure reasoning. Here are the steps: the artifice of the instrument depends either on one glass or on several. It cannot depend on one, for that must be either convex, or concave, or plain. The last form neither augments nor diminishes visible objects; the concave diminishes them, the convex increases them, but both show them blurred and indistinct. Passing then to the combination of two glasses, and knowing that glasses with plain surfaces change nothing, I concluded that the effect could not be produced by combining a plain glass with a convex or a concave one; I was thus left with the two other kinds of glasses, and after a few experiments I saw how the effect sought could be produced. Such was the march of my discovery, in which I was not assisted in any way by the knowledge that the conclusion at which I aimed was a verity.”

The telescope that Galileo presented to the Doge of Venice, and which was later lost, consisted of a tube of lead, with what is called a plano-concave eye-glass and a plano-convex object glass, and had a magnifying power of three diameters, which made objects look three times nearer than they actually were, and as a result nine times larger. The tube was about seventy centimeters long and about forty-five millimeters in diameter. It was first used in public from the top of the campanile in the piazza at Venice on August 21, 1609, and the most distant object that could be seen through it was the campanile of the church of San Giustina in Padua, about thirty-five kilometers away.

As soon as Galileo returned to his home in Padua he busied himself with improving his invention. First he constructed a new telescope, which as he said “made objects appear more than sixty times larger.” Soon he had a still better one, which enlarged four hundred times. He used this to examine the moon, and said that it brought that body “to a distance of less than three semi-diameters of the earth, thus making it appear about twenty times nearer and four hundred times larger than when seen by the unaided eye.” To use the instrument more accurately he built a support which held it firmly. He had also now learned to make the lenses adjustable, by fixing the tubes that held them so that they could be drawn out of, or pushed into the main tube of the telescope. To see objects not very far distant very clearly he would push the glasses a little way apart, and to see things very far distant he drew the glasses together.

But this last telescope did not altogether satisfy him, and so he built a still larger one. This brought objects more than thirty times closer and showed them almost a thousand times larger in size. With this he discovered the moons of Jupiter, and some of the fixed stars, and added much to what was already known concerning the Milky Way, a region of the sky which had long been a puzzle to astronomers.

He spent a great part of his time now in his workshop, making and grinding glasses. They were expensive and very difficult to prepare properly. Out of more than one hundred that he ground at first he found only ten that would show him the newly found moons of Jupiter. The object glasses were the more difficult, for it was this glass which had to bring to a focus as accurately as possible all the rays of light that passed into the telescope.

As the voyage of Columbus had brought a new world in the western ocean to the notice of Europe, so Galileo’s discoveries with his telescope brought forth a new world in the skies. Galileo wrote out statements of his discoveries, and sent these, with his new telescopes, to the princes and learned men of Italy, France, Flanders, and Germany. At all the courts and universities the telescopes were received with the greatest enthusiasm, and put to instant use in the hope of discovering new stars. But again the followers of Aristotle, those who were unwilling to admit that anything new could be learned about the laws of nature or the universe, arose in wrath. They attacked Galileo and his discoveries. They would not admit that Jupiter had four attendant moons, although these satellites could be seen by any one through the telescope, and a little later, when Galileo stated that the planet Saturn was composed of three stars which touched each other (later found to be one planet with two rings) they rose up to denounce him. But as yet these protests against the discoverer had little effect. Europe was too much interested in what he was showing it to realize how deeply he might affect men’s views of the universe.

Fame was now safely his. Men came from all parts of Europe to study under this wonderful professor of Padua. But teaching gave him too little time to carry on his own researches. So he looked about for some other position that would give him greater leisure, and finally stated his wishes to Cosimo II, Duke of Florence. Galileo had named the satellites of Jupiter after the house of Medici, to which this Duke belonged, and Cosimo was much flattered at the compliment. As a result he was soon after made First Mathematician of the University of Pisa, and also Philosopher and Mathematician to the Grand Duke’s Court of Florence.