Samuel Piper described this compressor in the Transactions of the Royal Microscopical Society of 1868. Its main advantage was the ability to turn the part holding the specimen to any angle including reversing it to view it from the opposite side, without removing the compressor from the stage, thereby keeping the specimen in view. It also had a rotatable cork disk for opaque specimens. This compressor had the added advantage of making it easy to remove the glass disks for cleaning or replacement by simply loosening the small knurled knobs holding the glass in place. Compression pressure is adjustable via the larger knurled knob on top. The slot on the bottom allows the compressor to swivel out of the center without the need to turn the compression device over or remove it from the stage, because the small cylinder extends slightly below the top of the support plate. The chief disadvantage of this compressor is the distance of the specimen holder from the stage, thus removing it from the range of most condensers and therefore making its use limited to low power observations unless a special condenser able to protrude above the stage can be fitted. Piper stated from the start that these were made by Swift and I have only seen them offered in Swift's catalogs. Although this one is unsigned, another signed example is shown on the page about the history of compressors. The compressor accepts 22 mm glass disks. Piper compressors rarely show up on the market for sale.