The restriction is necessary to protect the materials, as normal handling would speed up the rate of deterioration (not to mention wear and tear). For details on access, ask the reference librarians or write in to the National Library via this link.
"The Hikayat Abdullah 1849, autobiography of Malaccan Malay scholar, teacher & writer, Munshi Abdullah (1795-1854), is among the many precious items in the Rare Materials Collection."
Some samples of what's in the glass shelves:
(click to see larger images)
Tag: new national library, national library board singapore