Pseudorapidity distributions of charged particles produced in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mover><mml:mrow><mml:mi>p</mml:mi></mml:mrow><mml:mrow><mml:mi>¯</mml:mi></mml:mrow></mml:mover></mml:mrow></mml:mrow><mml:mi>p</mml:mi></mml:math>interactions as<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msqrt><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:msqrt></mml:mrow><mml:mrow><mml:mrow><mml:mrow/></mml:mrow></mml:mrow><mml:mo>=</mml:mo><mml:mn>630</mml:mn><mml:mn/></mml:math>and 1800 GeV

We present measurements of the pseudorapidity ($\ensuremath{\eta}$) distribution of charged particles ($\frac{d{N}_{\mathrm{ch}}}{d\ensuremath{\eta}}$) produced within $|\ensuremath{\eta}|\ensuremath{\le}3.5$ in proton-antiproton collisions at $\sqrt{s}$ of 630 and 1800 GeV. We measure $\frac{d{N}_{\mathrm{ch}}}{d\ensuremath{\eta}}$ at $\ensuremath{\eta}=0$ to be 3.18\ifmmode\pm\else\textpm\fi{}0.06(stat)\ifmmode\pm\else\textpm\fi{}0.10(syst) at 630 GeV, and 3.95\ifmmode\pm\else\textpm\fi{}0.03 (stat)\ifmmode\pm\else\textpm\fi{}0.13(syst) at 1800 GeV. Many systematic errors in the ratio of $\frac{d{N}_{\mathrm{ch}}}{d\ensuremath{\eta}}$ at the two energies cancel, and we measure 1.26\ifmmode\pm\else\textpm\fi{}0.01\ifmmode\pm\else\textpm\fi{}0.04 for the ratio of $\frac{d{N}_{\mathrm{ch}}}{d\ensuremath{\eta}}$ at 1800 GeV to that at 630 GeV within $|\ensuremath{\eta}|\ensuremath{\le}3$. Comparing to lower-energy data, we observe an increase faster than $\mathrm{ln}(s)$ in $\frac{d{N}_{\mathrm{ch}}}{d\ensuremath{\eta}}$ at $\ensuremath{\eta}=0$.