OBS. 18.—­After correcting the example.  “He knows nothing on [of] it,” Churchill remarks, “There seems to be a strange perverseness among the London vulgar in perpetually substituting on for of, and of for on.”—­New Gram., p. 345.  And among the expressions which Campbell censures under the name of vulgarism, are the following:  “’Tis my humble request you will be particular in speaking to the following points.”—­Guardian, No. 57.  “The preposition ought to have been on.  Precisely of the same stamp is the on’t for of it, so much used by one class of writers.”—­Philosophy of Rhet., p. 217.  So far as I have observed, the use of of for on has never been frequent; and that of on for of, or on’t for of it, though it may never have been a polite custom, is now a manifest archaism, or imitation of ancient usage.  “And so my young Master, whatever comes on’t, must have a Wife look’d out for him.”—­Locke, on Ed., p. 378.  In Saxon, on was put for more than half a dozen of our present prepositions.  The difference between of and on or upon, appears in general to be obvious enough; and yet there are some phrases in which it is not easy to determine which of these words ought to be preferred:  as, “Many things they cannot lay hold on at once.”—­HOOKER:  Joh.  Dict. “Uzzah put forth his hand to the ark of God, and took hold of it.”—­2 SAM.:  ib. “Rather thou shouldst lay hold upon him.”—­BEN JONSON:  ib. “Let them find courage to lay hold on the occasion.”—­MILTON:  ib. “The hand is fitted to lay hold of objects.”—­RAY:  ib. “My soul took hold on thee.”—­ADDISON:  ib. “To lay hold of this safe, this only method of cure.”—­ATTERBURY:  ib. “And give fortune no more hold of him.”—­DRYDEN:  ib. “And his laws take the surest hold of us.”—­TILLOTSON:  ib. “It will then be impossible you can have any hold upon him.”—­SWIFT:  ib. “The court of Rome gladly laid hold on all the opportunities.”—­Murray’s Key, ii, p. 198.  “Then did the officer lay hold of him and execute him.”—­Ib., ii, 219.  “When one can lay hold upon some noted fact.”—­Blair’s Rhet., p. 311.  “But when we would lay firm hold of them.”—­Ib., p. 28.  “An advantage which every one is glad to lay hold of.”—­Ib., p. 75.  “To have laid fast hold of it in his mind.”—­Ib., p. 94.  “I would advise them to lay aside their common-places, and to think closely of their subject.”—­Ib., p. 317.  “Did they not take hold of your fathers?”—­Zech., i, 6.  “Ten men shall take hold of the skirt of one that is a Jew.”—­Ib., viii, 23.  “It is wrong to say, either ’to lay hold of a thing,’ or ‘to take hold on it.’”—­Blair’s Gram., p. 101.  In the following couplet, on seems to have been preferred only for a rhyme: