Franz Christoph Khevenhüller, the Count of Frankenburg’s annuals were prepared on behalf of Emperor Ferdinand II and are among the most significant among Austrian historical sources. Although the author was only ten years old when Győr was retaken from the Turks, we find a chapter in this volume about that year when Ferdinand celebrated his twentieth birthday and was still only an archduke.

In this volume, something interesting caught the attention of engineer and technical science writer Aladár Pirovits, prompting further research.

After the miraculous victory on the night of March 28 to 29, 1598, the news courier set out from Győr in the usual manner. He covered about 500 km at breakneck speed and arrived in Prague on April 3 or 4 to deliver the news to Emperor Rudolf.

According to Khevenhüller’s account, however, he could not provide any new information to the monarch because he already possessed the information, and he even knew something that was not mentioned in Schwarzenberg’s message – which he allegedly did not even open. The king and his counselors astonished the messenger when they recounted how they knew the details of how, at what hour, the Pálffys blew up the Fehérvár Gate and other details of the street fights that followed.

King Rudolf was not known among historians for his governing abilities but rather for his paranoia, commitment to physical pleasures, arts, and sciences, as well as his passion for alchemy. He invited the most eccentric and advanced thinkers of the time to his court. One of the royal counselors told the skeptical courier that they learned the use of a device from an Englishman, allowing message transmission over several miles using moonlight.

Pirovits narrowed down the circle to a single English-born mathematician-astronomer in Rudolf’s Prague court during that time, Dr. John Dee, who could have shown them this version of mirror telegraphy. Only a compass – or as it was called then, a compass – and mirrors were needed, and in simple terms, it can be said that the parties communicated with each other using light signals between high points.

The interesting fact is that Gauss’s invention called the heliotrope, which used sunlight on the same principle, was born almost two and a half centuries later, in 1820!

The device referred to by Pirovits as “selenotrop,” functioning in the darkness of the night – especially in the night without light pollution of that time – could have been as effective as the heliotrope, which often used more intense sunlight. On a clear night, even if it was not a full moon (Count Khevenhüller claims it was a full moon on the night of victory, according to the perpetual calendar, it fell on March 23, 1598), the light signals were visible from a distance of 30-40 km.

Engineer and technical historian Ede Lósy-Schmidt also dealt with this question and drew the most probable line of telegraph stations between Győr and Prague with thirteen stations. Allegedly, it was easy to learn some signals that could quickly and accurately share a lot of information about the events.

Aladár Pirovits’ study reveals that this was the first documented application of moonlight telegraphy, which is significant not only from a Hungarian but also from an international perspective in the history of science. Beyond all this, it not only testifies to Emperor Rudolf’s enthusiasm for scientific novelties but also to the importance of the event they conveyed through it.

Not only Rudolf but also the eyes of Prague and Vienna were focused on Győr, as the success or failure of the attempt to liberate it from Ottoman rule could have had a decisive influence on the fate of the Austrian Empire – and Europe as a whole. It’s not surprising that they wanted to know as soon as possible if they had to prepare for defense against the Ottomans.

Instead, only good news arrived in Prague via the moonlight express, and by the time the courier arrived, the celebration had long been underway.