Index: OpenSceneGraph/trunk/include/osg/Referenced
===================================================================
--- OpenSceneGraph/trunk/include/osg/Referenced (revision 9343)
+++ OpenSceneGraph/trunk/include/osg/Referenced (revision 9549)
@@ -90,8 +90,8 @@
 
         /** Add a Observer that is observing this object, notify the Observer when this object gets deleted.*/
-        void addObserver(Observer* observer);
+        void addObserver(Observer* observer) const;
 
         /** Add a Observer that is observing this object, notify the Observer when this object gets deleted.*/
-        void removeObserver(Observer* observer);
+        void removeObserver(Observer* observer) const;
 
     public:
@@ -122,5 +122,5 @@
         struct ObserverSetData;
 
-        OpenThreads::AtomicPtr _observerSetDataPtr;
+        mutable OpenThreads::AtomicPtr _observerSetDataPtr;
 
         mutable OpenThreads::Atomic     _refCount;
@@ -131,5 +131,5 @@
         mutable int                     _refCount;
         
-        void*                           _observers;
+        mutable void*                   _observers;
 #endif
 };