I am interested in learning the purpose of the curve built into the shelves of record cabinets from the 20's to 40's.  According to a patron (I have not seen these myself nor do I have any expertise), most of the phonograph record cabinets he's come across feature a curve, or indentation, in the middle third of the shelf.  (I cannot figure out if he means a concavity to the shelf or that the curve of the shelf is such that, looking down at the shelf, one would see the curve cut into the shelf as to make it no longer rectangular.  I only have his written description which could be construed either way.)   He assumes the records were stored flat on the shelves.  Any insights as to the design purposes of the concavity or the curve?  Perhaps simply serving to help one grasp the records?  I assume someone familiar with the cabinets will be able to decipher my description, no easy task.
Hoping you can educate us.
Allen County Public Library
Fort Wayne, Indiana