173. In the figure below, valve $R$ is closed and the temperature of the trapped air in the tube is raised from 39 degrees Celsius. By how many degrees should the temperature be increased so that the height difference of the mercury columns in the two tubes increases by 2 centimeters? (The atmospheric pressure at the mercury level is 78 centimeters of mercury, and the diameters of the two tubes are equal. Neglect the volume of mercury.) [Figure: A U-tube manometer with valve R at the top, mercury columns with a height difference of $\Delta$cm indicated]
[(1)] 22
[(2)] 100
[(3)] 211
[(4)] 384
\textbf{173.} In the figure below, valve $R$ is closed and the temperature of the trapped air in the tube is raised from 39 degrees Celsius. By how many degrees should the temperature be increased so that the height difference of the mercury columns in the two tubes increases by 2 centimeters? (The atmospheric pressure at the mercury level is 78 centimeters of mercury, and the diameters of the two tubes are equal. Neglect the volume of mercury.)
\begin{center}
\textit{[Figure: A U-tube manometer with valve R at the top, mercury columns with a height difference of $\Delta$cm indicated]}
\end{center}
\begin{itemize}
\item[(1)] 22
\item[(2)] 100
\item[(3)] 211
\item[(4)] 384
\end{itemize}
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