Marchi, Monumenti delle arti cristiane primitive (Rome, 1844); Raoul Rochette, Tableau des catacombes de Rome (2nd ed., Paris, 1853) Perret, Les Catacombes de Rome (Paris, 1855) - a sumptuous folio work, but not always accurate; Roller, Les Catacombes de Rome (Paris, 1881); V.
When the crop is luxuriant it is necessary to put a roller over it first, to facilitate proper burial by the plough.
This device consists of a roller of radius r, pressed into contact with a disk.
The viscous mass having been thrown on the casting-table, a large and heavy roller passes over it and spreads it out into a sheet.
The shaft carrying the roller is connected to a counter so that 4 may be observed.