Christopher, a German Jesuit, born born at Bamberg, excelled in the knowledge of the mathematics, and was one of the chief persons employed to rectify the calendar; the defence of which he also undertook against those who censured it, especially Scaliger. He died at Rome in 1612, aged 75. His works have been printed in five volumes folio; the principal of which is his Commentary on Euclid's Elements.

**Clause**, in Grammar, denotes a member of a period or sentence.

Clause signifies also an article or particular stipulation in a contract, a charge or condition in a testament, &c.

**Clauenburg**, a large city of Transylvania, situated on the river Samos, in E. Long. 23° 20' N. Lat. 46° 53'.

**Clavus**, in antiquity, an ornament upon the robes of the Roman senators and knights, which was more or less broad, according to the dignity of the person; hence the distinction of tunica angusti-clavia and lati-clavia.

**Clavus**, in Medicine and Surgery, is used in several significations: 1. Clavus hystericus, is a shooting pain in the head, between the pericranium and cranium, which affects such as have the green sickness. 2. Clavus oculorum, according to Cellus, is a callous tubercle on the white of the eye, taking its denomination from its figure. 3. Clavus imports indurated tubercles of the uterus. 4. It also imports a surgical instrument of gold, mentioned by Amatus Lufitanus, designed to be introduced into an exsiccated palate, for the better articulation of the voice. And, 5. It signifies a callus, or corn on the foot.

**Clavus Annalis**, in antiquity. So rude and ignorant were the Romans towards the rite of their state, that the driving or fixing a nail was the only method they had of keeping a register of time; for which reason it was called clavus annalis. There was an ancient law, ordaining the chief prætor to fix a nail every year on the Ides of September; it was driven into the right side of the temple of Jupiter Opt. Max. towards Minerva's temple. This custom of keeping an account of time by means of fixing nails was not peculiar to the Romans; for the Etruscans used likewise to drive nails into the temple of their goddess Nortia with the same view.

**Claw**, among zoologists, denotes the sharp-pointed nails with which the feet of certain quadrupeds and birds are furnished.

**Clay**, in Natural History, a genus of earths, the characters of which are these: They are firmly coherent, weighty, and compact; stiff, viscid, and ductile to a great degree, while moist; smooth to the touch; not easily breaking between the fingers, nor readily fusible in water; and, when mixed, not readily subduing from it. See Chemistry and Mineralogy Index.

**Clay**, a town of Norfolk in England, seated on an arm of the sea between two rivers, in E. Long. 0° 30' N. Lat. 47° 28'.

**Clay-Lands**, those abounding with clay, whether black, blue, yellow, white, &c., of which the black and the yellow are the best for corn.

All clay-foils are apt to chill the plants growing on them in moist seasons, as they retain too much water; in dry seasons, on the contrary, they turn hard and choke the plants. The natural produce of clay foils is goose-grass, large daisies, thistles, docks, poppies, &c. Some bear clover and rye-grass; and, if well manured, produce the best grain: they hold manure the best of all lands; and the most proper for them are horse-dung, pigeons-dung, some kinds of marl, folding of sheep, malt-dust, ashes, chalk, lime, foot, &c.