\frametitle{Frankfurt: Home of Long-Distance AC Transmission}

  First long-distance high-voltage alternating-current transmission in 1891 from hydroelectric
  plant in Lauffen to Frankfurt for the Elektrotechnische Ausstellung (176~km, 15~kV).

  \begin{columns}[T]
\begin{column}{3.5cm}
  \includegraphics[trim=0 0cm 0 0cm,width=3.7cm,clip=true]{IEAFrankfurt1891c.jpg}
\end{column}
\begin{column}{2.5cm}
  \includegraphics[trim=0 0cm 0 0cm,width=2.8cm,clip=true]{Drehstromuebertragung_Lauffen-Frankfurt.png}
\end{column}
\begin{column}{5cm}
  \vspace{1cm}
        \includegraphics[trim=0 0cm 0 0cm,width=5cm,clip=true]{Lauffen-Frankfurt1891-1991.jpg}
\end{column}
  \end{columns}

  \source{Wikipedia}