The Tube with the Long Perspective

Paolo Sarpi had contacts all over Europe. At some point over Christmas 1608 he heard rumours that a spectacle-maker in the Netherlands had constructed a long tube. If one looked through it everything seemed to get closer and appear larger.

The Servite monk was not especially interested in it himself, but when the rumours got louder, and one considered the military implications such an instrument might have, he mentioned the phenomenon to his friend Galileo, one evening in June 1609 when the professor was on a visit to Venice.

The inventor of the geometric and military compass realised immediately that here was a completely new opportunity. Whereas the compass could merely calculate the distance to the enemy's emplacements, this new instrument could display them! The "spyglass" was, at the same time, a practical and intellectual challenge and possibly a financial godsend.

Galileo grasped that the secret was connected with lenses, of the sort spectacle-makers used. As Venice was a glass manufacturing centre, it was easy to get hold of a suitable selection of different lenses. He then travelled straight home to Padua and began work.

He was not acquainted with any practical theory of refraction, so he felt his way forward by trial and error. The instrument was shaped like a tube, so it was reasonable to assume there was a lens at each end, with a certain distance in between. But what type of lenses? There were curved lenses of two types, convex and concave, and one that was flat on one side and curved on the other.

After a day's experimenting Galileo had a primitive telescope. He placed a plano-convex and a plano-concave lens in a tube and got an out-of-focus image of distant objects, magnified some three or four times. Proudly he returned to Venice by water and showed the result to Sarpi and other friends: whatever foreign inventors could do, the Republic's own professionals could easily copy and surpass it!

His friends kept the telescope. Galileo returned to Padua to carry on the work.

He was fully aware that the instrument was not good enough, and that improved versions would certainly be made by others. So he attempted to understand the theory behind its operation, and at the same time he learnt to polish glass.

Meanwhile Sarpi and the others exerted themselves in Venice. They contacted the Senate, demonstrated and boasted about the new invention. Galileo was praised and promised better pay, and he worked on conscientiously with his lenses. By August everything was ready for the big demonstration.

Once again Galileo was clambering to the top of a belfry, this time the slender and lovely detached campanile in Venice's famous Piazza San Marco.

With him, up the winding, stairless climb went the leading men of the Republic, senators and others. He carried the instrument himself; he called it a cannocchiale. The tube felt heavy in his hands - it was made of lead and covered with a crimson cotton fabric. It was about sixty centimetres long and fairly narrow.

The day was crystal clear. From the top of the tower one hundred metres above San Marco, the view stretched in all directions.

Each of those invited tried it in turn. They placed the tube to one eye, closed the other, and pointed it over the lagoon.

One of the men pointed the tube to the north, towards the glass-manufacturing island of Murano, about a mile off. He had a little trouble locating the church of San Giacomo within the small field of vision but, once found, he could clearly make out the people who were going in and out of the church door. A little way off a gondola was tied up on the Glass-makers' Canal, and people were disembarking.

Another turned it to the south-west and followed the coastline with the glass. He saw something that had to be Fusina, the place where the canal from Padua disgorged. And so they went on, round the horizon - until one senator caught sight of something that surely was a distant cupola or campanile far inland. He pointed, they discussed the direction, several others took a look - and then they agreed: it must be Santa Guistinia at Padua!

Galileo had enabled them to look out across the plain from Venice's highest tower and see all the way to the city where he lived.

Venice looked outwards, towards the Adriatic. The sea brought riches to the Republic - but also threats. None of the senators was in any doubt about the implications of Galileo's cannocchiale: an enemy ship could be observed several hours sooner, and the defenders could get an idea of its size and armament.

After the convention of the times, Galileo had presented his invention to Venice and its Senate. He was an academic, not an artisan who sold his services. It was up to the administrators to show how much they appreciated his gift. He could hardly complain about their response: the professorship at Padua was his for life, and his salary was almost doubled to the handsome, round sum of 1,000 scudi per annum. It was taken as read that he would not divulge the workings of the magic tube to anyone else.

But here the Senate made a miscalculation. A sceptical Tuscan agent in Venice reported to the Grand Duke's court: "It is said that in France and in other places the secret is already well known, and can be bought for a small sum." And then, just a couple of weeks later: "Signor Galileo's secret, or 'the tube with the long perspective' is now being sold here publicly by a certain Frenchman..." The agent had, however, to admit that Galileo's telescopes were far superior, a supremacy which - thanks to the professor's practical ability and technical insight - was to continue for several years.

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