Lowth amplified Dryden's anxiety over placing a preposition at the end of a sentence:

He is well aware that this is a normal English-speaking practice in informal usage. 

The 'strong inclination' can in fact be traced back to early Middle English. But doubtless the etymology of the word weighed heavily with him: if it is a preposition, it must go before, not after; and he concludes:

The last part of this sentence is accurate enough: it is indeed the case that the difference between the two constructions is one of formality. That's the bus I was travelling in is much more informal than That is the bus in which I was travelling. And if Lowth had gone on to recommend that both be used in their appropriate circumstances, informal and formal, there would be no quarrel today. 

But that is not what prescriptive grammarians are for. Their role is not to recognize and applaud variety, but to condemn and eliminate it. Lowth, as Murray after him, wants only the formal alternative to be used. The argument about perspicuity is totally beside the point: it is not the case that one version is any more or less clear than the other. The two sentences are synonymous. And the argument from gracefulness is irredeemably subjective: what Lowth might consider graceful another writer might consider graceless. 

Nor are prescriptive grammarians very good at avoiding the practices that they are in the process of condemning. In the above prescription, Lowth actually ends one of his sentences with a preposition: "... which our language is strongly inclined to." Murray, taking over the point wholesale, must have noticed, for in his Grammar he corrects it: "This is an idiom to which our language is strongly inclined." But even Murray lets his guard down from time to time: on p. 40 of his book we read "so convenient is it to have one acknowledged standard to recur to." 

Lowth then lists a number of bad examples, which ought to be avoided in an age of politeness. They include two Shakespearean instances: Who servest thou under? from Henry V, and Who do you speak to? from As You Like It. The implication is plain: if even Shakespeare can get it wrong, what chance do ordinary people have? But there is a solution: face can be saved by following the practices recommended by the grammarian. 

And good practice could be achieved only by practice. Here are two of the test sentences relating to end-placed prepositions in Lindley Murray's follow-up book: English Exercises, Adapted to the Grammar Lately Published, which appeared in 1797. Section 5 (p. 174) adumbrated: "A fifth rule for the strength of sentences, is to avoid concluding them with an adverb, a preposition, or an inconsiderable word." 

The Key at the back of the book tells us that the correct versions are upon which I am to proceed and of which many persons are very fond. The examples are plainly formal in character, and if we sense a stylistic inelegance, especially in the first sentence, it is due to the inconsistency of using both preposed and postposed prepositions in the same construction (by what ... proceed upon). The utterance is plainly part of a discourse of some intellectual content, requiring carefully articulated expression, and it is disturbing to see it change stylistic level halfway through. Such observations could form part of an instructive lesson on English style, in which the stylistic force of the alternative constructions would be compared and contrasted. 

But that is not how things went. Schoolchildren learned a black-and-white rule: one should never end a sentence with a preposition. As Winston Churchill was later to remark: that kind of English was something up with which he would not put.