kw: history, historical linguistics, typography
In the original manuscript of the Bill of Rights, the word "Congress" is seemingly spelled "Congre⌠s" or even "Congrefs" to many eyes. That funny letter before the final "S" is the "Medial S" and was used everywhere except where S was the last letter, prior to about the year 1800. There are plenty of discussions of the medial S available, and that isn't my point here anyway. Rather, it is that with the help of the Google Labs Ngram tool, we can see the change take place.
As the Google Labs people explain in their "About Ngram" information, the medial S in older documents was OCR'd to an F, so that we need to be wise when searching older documents. Here is a search for both "wish" and "wifh":
You can actually see the change take place. You can also see that the medial S seems to have arisen about 1630 but become common only after 1660. Either Google is fixing older books' renderings, or only the common S was used in the oldest books.
By making a run with "wish,wifh,desire,defire" (not shown), I found that "desire" (+"defire") has a rather steady frequency going back to 1600, but, as we see here, "wish"+"wifh" grew from a low level early on prior to 1800. Since about 1800 the two words have very similar frequencies.
Does the downslope from 1850 to 2000 indicate a reduction in wishfulness? Further study may ferret that out.