**4. Conclusions**

The optical telegraph of Agustín de Betancourt and Abraham Louis Breguet is one of the most important legacies in the history of engineering. Not surprisingly, it was the first telegraph that operated in the Iberian Peninsula and it was one of the first in the world to operate.

This article has had as its main objective to obtain 3D modeling and virtual reconstruction of this invention respecting its original project to the maximum detail, using the Autodesk Inventor Professional software. Thanks to this 3D modeling, it has been possible to explain in detail both its operation and the assembly system of this invention in a coherent way, allowing us to discover the virtues of the invention and the advantages it presented from the point of view of engineering over its contemporary telegraphs.

The methodology employed in this research has been based on our knowledge of descriptive geometry and the use of direct empirical measurement techniques on the three drawings of the invention file which presented a graphic scale. Thus, after modeling each element of the set with the abovementioned parametric design and engineering software, it was necessary to establish restrictions (dimensional, geometric, and of movement) as well as of joints in order to obtain a coherent and fully functional 3D CAD model.

From this 3D CAD model it has been possible to obtain detailed geometric documentation of each element, as well as an axonometric view, a plan of the ensemble with an indicative list of all the elements and their material, and an exploded view with indication of each element in the assembly, which has made it very easy to fully understand the detailed operation of the assembly and the function of each element within it.

Among the main discoveries, it has been found that the transmissions in the telegraph were not performed by hemp ropes rather by metal chains with flat links, since the error introduced was much smaller than with the use of ropes. Similarly, it has also been found that the use of the gimbal joint facilitated the adaptability of the invention to geographical areas where there was a physical impediment for the telegraph stations to be aligned and, in addition, facilitated the non-obligation of the telescope frames to be parallel to the frame of the indicator arrow, thus enabling them to work in different planes.

This research methodology can be applied to a multitude of technical historical heritage inventions studied over the centuries and will allow us to rescue these notable contributions of technology to society, highlighting their legacy thanks to the techniques of modeling and virtual reconstruction as a first step towards a CAE study.

**Author Contributions:** Formal analysis, E.D.l.M.-D.l.F.; funding acquisition, J.I.R.-S.; investigation, J.I.R.-S. and E.D.l.M.-D.l.F.; methodology, J.I.R.-S. and E.D.l.M.-D.l.F.; project administration, J.I.R.-S.; supervision, J.I.R.-S.; validation, E.D.l.M.-D.l.F.; visualization, J.I.R.-S.; writing—original, draft, J.I.R.-S. and E.D.l.M.-D.l.F.; writing—review and editing, J.I.R.-S. and E.D.l.M.-D.l.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the Spanish Ministry of Economic Affairs and Competitiveness under the Spanish Plan of Scientific and Technical Research and Innovation (2013–2016), and the European Fund for Regional Development (EFRD) under grant number [HAR2015-63503-P].

**Acknowledgments:** We are very grateful to the Fundación Canaria Orotava de Historia de la Ciencia for permission to use the material of Project Betancourt available at their website. Similarly, the authors of the article express their sincere thanks to Pedro Jesús Pancorbo Rico for his work with the initial CAD model used in this research. Also, we sincerely appreciate the work of the reviewers of this article.

**Conflicts of Interest:** The authors declare no conflicts of interest.
