*3.2. Optical Telegraph Assembly Process*

The Betancourt and Breguet optical telegraph was a simpler mechanism to assembly than any of the contemporary telegraphs, although in any case it is a structure that when its mast and arrow are aligned has a minimum total height of 9.85 m (if it is true that, depending on the needs of the location, it could reach more than twenty meters high). A precision mechanism of these dimensions requires a fairly careful assembly, and therefore the study of the mechanism and its modeling using CAD techniques has enabled the authors of the article to gain a special awareness of the delicate assembly of the telegraph which we will now describe.

In the first place, for the correct assembly of the telegraph, it is necessary to judiciously choose the location of the telegraph station. The operator should have a direct and clear view of the immediate stations. Thus, a location aligned as much as possible with respect to the preceding and subsequent station was chosen, facilitating installation and reducing the possible optical error. Once this location was chosen the plane of the telegraph (plane defined by the circumference described by the indicator arrow) was located as parallel as possible to the planes of the immediate telegraphs, and if this was impossible to measure (there were already compasses at the time), taking the direction perpendicular to the one drawn by the segment that joined the immediate telegraphs. Thus, the frame that held the mast (3) should be perfectly aligned knowing these data, and the structure of the mast should not be raised until a series of elements were placed on it, since once it was lifted it, would be necessary to place a large structure to assemble the rest of the elements.

With the mast on the ground, the first element that was to be placed was the winch (9) with its axis, positioning it perpendicular to the structure of the mast. Once in position the shaft had to be fixed by placing the two gimbal joints on the outer faces of the frame, which do not prevent the shaft from rotating but do prevent its axial movement.

The next operation was to place the upper wheel (12) with its own axle. In order to do this, the axle had to be placed in its exact location, the wheel housed and finally the metal structure fixed which gave a second point of support to the axle. Thus, the wheel and the winch were still in place to insert the main transmission (11) before lifting the mast. The main transmission was one of the most delicate elements to place in the mechanism. As explained in the description of the invention, the main transmission was formed of a middle zone and two extreme zones. The middle zone was constituted by a hemp rope and the extreme zones were two chains of flat links, and the join of both elements was achieved by means of a tensor that when turned moved its ends closer together. For the assembly of the main transmission one of the tensors needed to be detached from the two ends. Thus, the part of the chain transmission was placed both in the groove of the wheel (12) and in the groove of the winch (9) and once in position the tensor was put in place and the main transmission tensioned (11). This operation had to be performed at least twice since the transmission was double, that is to say there were two main transmissions in parallel. Once it had been verified that, when turning the winch, the upper wheel turned in the same direction, it was time to lift the structure.

In order to raise and fix the structure two ropes (10) were necessary, acting as struts of about 12 m in length, which served to give stability to the structure and prevent its swaying. One end of the rope was tied to the head of the mast while the other was attached to an anchor in the ground. Moreover, the structure of the mast has a counterweight on the side opposite the arrow that also supports the mast, which also helps to gain stability in the structure. Finally, once the structure was lifted, it was fixed to the ground by two long anchor bolts.

After this operation the frames (6) of the telescopes were installed. This was one of the most delicate tasks since the frame had to be fixed to the ground once the telescope was pointing in the right direction, something that was also achieved by means of anchor bolts, and in order to obtain the correct direction it was essential to have a signal indicating at least the position of the immediate telegraphs. Thus, once the two frames were oriented, the telescopes were placed and fixed (5) by means of a wooden clamp which allowed them to rotate but not to move axially. The telescopes on the other hand were not normal since the end of the telescope's eyepiece was housed in a pulley (7). Once the telescope was placed and after making sure that it pointed clearly to the nearest station, it was rotated until the meridian wire in the eyepiece was arranged vertically.

The transmission mechanism between the telescope pulley and the winch made it easy to control the position of the telescopes from the winch. The gimbal joint was connected by a pin to a pulley (8), and this through a lower transmission (4) communicated the movement to the telescope pulley (7). The assembly process, therefore, was very similar to that of the main transmission: first the gimbal joint pulley (8) was mounted by the aforementioned pin, and then the transmission was placed on them, inserting the chain into the grooves perimeter of both pulleys. The transmission also had a central part of hemp rope and two extreme zones of flat metal links. In the assembly process, it was very important that both the telescope and the winch were fixed in the same position (the meridian wire in vertical position and the winch pointing to the vertical position of the indicator arrow). Again, one of the two link chain tensors had to be detached from it while the lower transmission was placed in its position and tightened until it was tight. This operation had to be performed twice, once for each telescope.

The final step to finishing the assembly was the placement of the indicator arrow (2) on its axle. Obviously this process was simple if the mast measured only a few meters, but if the mast measured more than 10 m the process presented more complexity, since it was necessary to install the structure using a crane and with the help of many operators, because the indicator arrow alone measured 6.60 m. The indicator arrow mounted separately with its three oil lamps (1) and its transverse base should be placed on its axle in an upright position and with the horizontal arm in the position closest to the ground. Once inserted it should be fixed to the horizontal axle by four bolts in order to secure it perfectly. This horizontal axle was undoubtedly the piece that was going to endure the majority of the stresses to which the mechanism would be subjected, and the useful life of the mechanism depended on its correct installation. After this step, the mechanism would be in perfect condition for use.
