Galileo telescope internal construction for Griffith Observatory IMSS The Institute and Museum of the History of Science Florence Italy

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Construction Details of Galileo's Telescope Tube and Lens Holders.

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09/18/2007 07:44:17 PM Last updated

Construction Details of Galileo's Telescope Tube and Lens Holders.

Studying Galileo's Telescope in detail disclosed a unique resin composite construction. It is not made of cardboard and paper as is often reported in the literature This discovery gave us the opportunity to study the methods and philosophy of construction available to and generated by Galileo, his associates, and assistants in their scientific and engineering work. This work has raised some interesting academic and replica questions. 1.Was it designed for "mass production" by non skilled labors? 2, was the eyepiece lens the only part replace or was the lens holder also changed? Studying the original in some detail has helped us in our mission to construct a much more faithful reproduction inside and out of this famous Galileo telescope for the Griffith Observatory.

As mentioned earlier we were very fortunate in addition to our measurements and photographs of this beautiful Galilean telescope to also have access to excellent pictures taken before and after a recent restoration. These pictures showed that the internal construction of the telescope is not of cardboard and paper but of wood and in a most novel way. This opened to us a very rare opportunity of making a very fine replica in the most complete and accurate detail even to the interior. This accuracy of course helps to show the inventiveness and creativity of how scientist worked in 1600. It shows along with its history the on going issues and struggle of the basic research scientist trying to get support for their research and acceptance of its results. This telescope and its history shows ----Not only the technical aspects of science ---- but the politics of funding for basic research work, of the struggles in convincing others to see the world more clearly from a scientific measurement point of view. This telescope served as a political tool as well as a discovery tool. It was designed to impress people not of science but of power and wealth by the richness of its decorative appearance. it was also preformed well, 20 power, to show them his discoveries.

The data we collected were vital in making a truly faithful replication of both inside and the outside of this remarkable telescope. Many if not all replicas of this telescope in the past have not had this opportunity or not felt it worth while to go beyond the use of cardboard, plastic or metal tubes and turned solid wood lens holders none of which were used in the original instrument. Some have had to replicate the telescopes without accurate data thus included in some cases serious errors in their replication. We believe that this is unfortunate and scales down the broadness and richness of what is to be learned from this telescope. We feel, perhaps unfairly, that the lack of detail and authenticity only increases the myopic view for some of what science is all about.

Below we show you the detail of the very elegant mode of construction and the amount of detailed work that was required to make it.*

Figure 1 One end of the tube of the telescope Photo courtesy IMSS

Figure 2 One of the lens holder Before Restoration Photo courtesy IMSS

Comments about the construction.
From a casual point of view the construction technique is novel to say the least, to some it looks like a poor design. See figure 3.Barrel like tube construction requires the edges of the staves to be chamfered butting up to each other if it is to have radial strength . Without careful attention to these gaps it weakens the radial strength of the tube and will collapse on its self See in figure 4.

All these issues disappear when one notes that the builder used a resin glue, which had to be liberally applied layer by layer soaking into all the cracks and filling all the gaps. This is a method that we today call a resin composite construction. It consists of bonding all of the materials and parts of the telescope together with a resin. The resulting structure has physical characteristics superior to the components by themselves. Ref. 1

Choice of cutting strips, and importance of keeping them in order. Tests of hide glue gives good filling characteristics and has adequate strength. Sticking the sticks together.

Figure 3 shows how the tubes were built It was a construction that was used on both the telescope tube and the lens holders, the latter having upwards 2 to 5 layers until the tube were the right size and strength.
We built a small section using this construction technique to demonstrate how it might be made and to test its strengths and weakness. for the replica.
It's a strake-style construction comprised of a number of strips of wood fixed on a thin flexible backing and rolled into a tube. It's easy to build but note the gaps on the outside. The tube strength depends markedly on the treatment of these gaps. Without a filler between them the junctions would collapse on themselves with very little pressure . We show this in figure 4.

Figure 4

The telescopes strength--
In preparing the first layer for the second, resin glue is put on the outer surface of the 1st. thus fills its gaps. Preparing the second surface for the third fills the second layer gaps, and so on to the final step. At this point one has saturated the whole tube layer by layer generating a resin composite construction which is light and strong using a minimum of simple tools. A process that lends its self to mass production.

Figure 4A, Simple construction steps which do not require a lathe. Note the tube can be squished as in 4C, a" feature" making the joint gluing easier. It only requires a simple square not cylindrical mandrel.

Strips of wood are cut from a single sheet. These cuts don't have to made with precision and in fact are rarely straight when done by hand. But when the pieces are kept in sequence the gaps between them maintain a uniform width. See inset photo in A.
A, Strips of wood glued to backing
B, Strips bent in to tube form
C, Tube is clamped while glue is setting
D, Tube ready for next layer

Figure 5 Second layer
A test section showing the novel construction used in the number 2 Galilean Telescope. Today we call this a resin composite construction. Its light, strong and cheap. It resist a 100 lbs crushing force.


Part of the telescope body and sliding tube lens holder.	Wood staves for telescope and lens holders.	The wooded structure ready for the leather covering, art work and lenses.