WIP: Electromagnetic spectrum

1 files changed, 6 insertions, 2 deletions

diff --git a/chapter00/preface.tex b/chapter00/preface.tex
index 11cb160..097de33 100644
--- a/chapter00/preface.tex
+++ b/chapter00/preface.tex
@@ -18,10 +18,10 @@ Transferring information became more important as societies advanced.
 	\item People all over the world used drums or other devices to generate sounds.
 	\item Some Native Americans tribes used smoke signs to communicate over large distances.
 	\item The invention of paper simplified communication. Large amount of information could be stored and transferred.
-	\item An example of more sophisticated communication technology is the \index{Caesar cipher} Caesar cipher used in the Roman Empire in ancient times. It is one of the first devices developed for cryptography.
+	\item An example of more sophisticated communication technology is the \index{Caesar cipher} Caesar cipher (Figure \ref{fig:preface:caesar_cipher}) used in the Roman Empire in ancient times. It is one of the first devices developed for cryptography.
 	\item Homing pigeons delivered letters over long distances.
 	\item In the Middle Ages, beacons were used in defensive communication to relay a signal.
-	\item In the 18th century, semaphore lines had been built. They used visual telegraphy. Semaphores on fixed towers could display a set of symbols, which were relayed along the line.
+	\item In the 18th century, semaphore lines had been built. They used visual telegraphy (Figure \ref{fig:preface:optical_telegraph}). Semaphores on fixed towers could display a set of symbols, which were relayed along the line.
 \end{itemize}
 
 \begin{minipage}{0.45\linewidth}
@@ -29,6 +29,7 @@ Transferring information became more important as societies advanced.
 		\centering
 		\includegraphics[width=\linewidth]{../chapter00/CaesarCipher.jpg}
 		\caption[Caesar cipher]{Caesar cipher. Each letter is replaced by another one which is a fixed number of letters away from the original one. \licensequote{\cite{Berberich2013}}{Hubert Berberich}{Public Domain}}
+		\label{fig:preface:caesar_cipher}
 	\end{figure}
 \end{minipage}
 \hfill
@@ -37,6 +38,7 @@ Transferring information became more important as societies advanced.
 		\centering
 		\includegraphics[width=\linewidth]{../chapter00/OpticalTelegraph.jpg}
 		\caption[Optical telegraph]{Optical telegraph \cite{WikiSemaphore}}
+		\label{fig:preface:optical_telegraph}
 	\end{figure}
 \end{minipage}
 
@@ -82,5 +84,7 @@ Understanding digital communication systems is of great importance in many engin
 	\item \textbf{Energy Sector} -- Smart grids rely on information exchange between energy producers and energy consumers. Communication technologies enable an efficient control of the power network.
 \end{itemize}
 
+\phantomsection
+\addcontentsline{toc}{section}{References}
 \printbibliography[heading=subbibliography]
 \end{refsection}