Ceratonia siliqua harubh. "Ceratonia siliqua", the scientific name of the carob tree, derives from the Greek "kerátiοn" κεράτιον 'fruit of the carob (from "keras" κέρας 'horn'), and Latin "siliqua" 'pod, carob'. The unit "carat", used for weighing precious metal and stones, also comes from κεράτιον, as alluding to an ancient practice of weighing gold and gemstones against the seeds of the carob tree by people in the Middle East. The system was eventually standardized, and one carat was fixed at 0.2 grams. In late Roman times, the pure gold coin known as the "solidus" weighed 24 carat seeds (about 4.5 grams). As
How many angels can dance on the head of a pin? about how many could perch at the same time on the head of a pin"". Dorothy L. Sayers argued that the question was "simply a debating exercise" and that the answer "usually adjudged correct" was stated as, "Angels are pure intelligences, not material, but limited, so that they have location in space, but not extension." Sayers compares the question to that of how many people's thoughts can be concentrated upon a particular pin at the same time. She concludes that infinitely many angels can be located on the head of a pin, since they do not occupy any space there: