OBS. 4.—­Of these letters, Day gives this account:  “M. denotes mille, 1,000; D., dimidium mille, half a thousand, or 500; C. centum, 100; L. represents the lower half of C., and expresses 50; X. resembles V. V., the one upright, the other inverted, and signifies 10; V. stands for 5, because its sister letter U is the fifth vowel; and I. signifies 1, probably because it is the plainest and simplest letter in the alphabet.”—­Day’s Punctuation, p. 103.  There is some fancy in this.  Dr. Adam says, “The letters employed for this purpose [i.e., to express numbers.] were C. I. L. V. X.”—­Latin and Eng.  Gram., p. 288.  And again:  “A thousand is marked thus CI[C-reverserd], which in later times was contracted into M. Five hundred is marked thus, I[C-reversed], or by contraction, D.”—­Ib. Day inserts periods thus:  “IV. means 4; IX., 9; XL., 40; XC., 90; CD., 400; CM., 900.”—­Page 703.  And again:  “4to., quarto, the fourth of a sheet of paper; 8vo., octavo, the eighth part of a sheet of paper; 12mo., duodecimo, the twelfth of a sheet of paper; N. L., 8 deg.., 9’., 10’’., North latitude, eight degrees, nine minutes, ten seconds.”—­Page 104.  But IV may mean 4, without the period; 4to or 8vo has no more need of it than 4th or 8th; and N. L. 8 deg. 9’ 10’’ is an expression little to be mended by commas, and not at all by additional periods.

OBS. 5.—­To allow the period of abbreviation to supersede all other points wherever it occurs, as authors generally have done, is sometimes plainly objectionable; but, on the other hand, to suppose double points to be always necessary wherever abbreviations or Roman numbers have pauses less than final, would sometimes seem more nice than wise, as in the case of Biblical and other references.  A concordance or a reference Bible pointed on this principle, would differ greatly from any now extant.  In such references, numbers are very frequently pointed with the period, with scarcely any regard to the pauses required in the reading; as, “DIADEM, Job 29. 14.  Isa. 28. 5. and 62. 3.  Ezek. 21. 26.”—­Brown’s Concordance.  “Where no vision is, the people perish, Prov. xxix. 18.  Acts iv. 12.  Rom. x. 14.”—­Brown’s Catechism, p. 104.  “What I urge from 1.  Pet. 3. 21. in my Apology.”—­Barclay’s Works, iii, 498.  “I.  Kings—­II.  Kings.”—­Alger’s Bible, p. iv.  “Compare iii. 45. with 1.  Cor. iv. 13.”—­Scott’s Bible, Pref. to Lam.  Jer. “Hen. v.  A. 4.  Sc. 5.”—­Butler’s Gram., p. 41.  “See Rule iii.  Rem. 10.”—­Ib., p. 162.  Some set a colon between the number of the chapter and that of the verse; which mark serves well for distinction, where both numbers are in Arabic figures:  as, “’He that formed the eye, shall he not see?’—­Ps. 94:  9.”—­Wells’s Gram., p. 126.  “He had only a lease-hold title to his service.  Lev. 25:  39, Exod.