As I recall, this issue has been addressed previously.
(yes, it's that 18 month cycle again!)
To search the list's archives, please go to
http://home.ease.lsoft.com/archives/museum-l.html
-Steve
Steven Eichner, Research Analyst and List Manager
Association of Science-Technology Centers Inc., Washington, DC
email: [log in to unmask]; web: http://www.astc.org
ph: 202/783-7200x130; fax: 202/783-7207