diff --git a/Cantera/src/Phase.h b/Cantera/src/Phase.h
index 1ab8be720..09e6cca05 100755
--- a/Cantera/src/Phase.h
+++ b/Cantera/src/Phase.h
@@ -184,7 +184,15 @@ namespace Cantera {
 	 *    become hidden.
 	 */
 	int m_kk;
+	/**
+	 * m_ndim is the dimensionality of the phase. Basically, volumetric phases
+	 * have dimensionality 3 and surface phases have dimensionality 2.
+	 */
         int m_ndim;
+	/**
+	 * m_index is the index of the phase
+	 * 
+	 */
         int m_index;
 
     private: