Undated Map of Optical Telegraph Stations in France
Courtesy of Low-Tech Magazine via Ecole Centrale de Lyon
Centuries of slow long-distance communications came to an end with the arrival of the telegraph. Most history books start this chapter with the appearance of the electrical telegraph, midway the nineteenth century. However, they skip an important intermediate step. Fifty years earlier (in 1791) the Frenchman Claude Chappe developed the optical telegraph. Thanks to this technology, messages could be transferred very quickly over long distances, without the need for postmen, horses, wires or electricity.
The optical telegraph network consisted of a chain of towers, each placed 5 to 20 kilometres apart from each other. On each of these towers a wooden semaphore and two telescopes were mounted (the telescope was invented in 1600). The semaphore had two signalling arms which each could be placed in seven positions. The wooden post itself could also be turned in 4 positions, so that 196 different positions were possible. Every one of these arrangements corresponded with a code for a letter, a number, a word or (a part of) a sentence.
The other day I found this tremendously enlightening article about optical telegraphs on Low-Tech Magazine. Prior to reading this article I had no idea about this arcane method of communication. The authors supplied a map (above) to really drive home how extensive this system was.
Something that I think few people do when surfing through Wikipedia is to check the articles in other languages. It’s really easy to do and the results tend to be very useful. For words that have equivalent spellings, all one has to do is change the URL’s prefix (fr to en). For words that have different spellings (telegraph vs télégraph) you will have to correct this spelling in order for the entry to show up.
For example, the French entry on telegraphe yields quite a bit more information related to the use of semaphores (the object used to construct the optical telegraphic code) than the English entry on telegraphs.
Below is a carte of the semaphoric number system and an engraving of Mont St. Michel with a semaphore at the top. Both images obtained from the French wikipedia.
+ MORE
Getting to know Mr. SID
|| 1/7/2008 || 3:13 pm || Comments Off on Getting to know Mr. SID || ||
Screen grab from the Library of Congress which DOES NOT list Graphic Converter as an option…. yet?
For the last few years I’ve found the file format Mr. SID to be the bane of my cartographic explorations. When I’d see a map available in the MultiResolution Seamless Image Database format, it meant I’d have to keep looking for other maps. Conversion of the Mr.SID format on a Macintosh had kept the maps locked away in an obscure file format; smiting me.
In my opinion, one of the worst decisions that the Library of Congress made was the choice to use the Mr.SID file format for their on-line maps. First off, its a proprietary compression algorithm patented by a company that is motivated by profit, not by the intent of furthering academic research. This means that any software maker originally had to get a license (pay) to use it. This resulted in only a few programs being written that can convert the file type. Worse is that there are even fewer Macintosh-based programs that can convert these files. The patent owner’s website offers only one Macintosh product and does not allow the rendering of the map at it’s full size. As in, I could only export sections of the original map, which makes the reader useless. Secondly, the file type is in itself “an American Memory,” because its not widely used anymore. It made sense to use it originally- it saved server space because of the high compression algorithm, but now server space is relatively cheap. Today only people who use high-end GIS software use Mr.SID formated imagery, and since most of this software only exists on PCs, there has been little cross platform support. Lastly, for any maps to be used by an image editing program, the map must first be converted out of the Mr.SID format and converted into another filetype (.jpg, tiff, etc.). This means that for every map that is available on the Library of Congress website, I have to spend 15 minutes converting it to a useful format.
Over the weekend I discovered that there is *one* program for Macintosh that can convert this file type: Graphic Converter. I also discovered that the newsest version (the Universal Binary, which I downloaded last summer) did not handle Mr.SID. Instead, I had to download an obsolete version (Graphic Converter for PowerPC) to convert this arcane format! So for the last 7 months I had been unable to convert any Mr.SID formatted map, but now I can, and I’m very excited about the new possibilities this opens up (literally hundreds of maps are now within virtual reach! The Library is only a few blocks away, but the digitalization is just as important.).
I sincerely hope the Library of Congress updates the page above to list Graphic Converter as one of the programs that can convert Mr.SID formatted maps. This software program is already listed for use with other media on the same Library of Congress webpage. Also of note, is that Graphic Converter can also convert JPEG2000 encoded maps.