P.S.--I may add that, with respect to these words "happy low lie down," from my habit of looking for solutions of difficulties in parallels and antitheses, I have arrived at a different conclusion from any that has yet been suggested. Finding "uneasy" used _adverbially_ in the last line, I see no reason why "happy" should not also be taken _adverbially_ in the preceding line: we should then have the same verb, "lie" and "lies," repeated antithetically in the same mood and tense.
The article _the_ before "low" has probably been omitted in the press, and may be either actually restored or elliptically understood:
"Then _happy_ [the] low lie down; _Uneasy_ lies the head that wears a crown."
Between the years 1803 and 1830, a gentleman resident of London, under the signature A. Z., presented from time to time to the Society of Antiquaries of Scotland, a collection of works respecting the Orkney and Shetland islands, copiously illustrated with manuscript notes and inserted prints, maps, &c. The internal evidence leaves no room to doubt that the donor of this valuable collection was a native of Kirkwall; and recent investigations lead to the conclusion that he was a Mr. John Munro, originally in the office of Mr. John Heddle, Town Clerk of Kirkwall. He appears to have gone to London about 1789, and to have passed the rest of his life there, down to May, 1830, when his last communication was made to the Scottish Antiquaries. A list of his donations is printed in the _Archæologia Scotica_, vol. iii. pp. 267-274. His copious manuscript notes, written in a very neat and legible hand, indicate not only a man of intelligence and research, but also of an exceedingly amiable and kindly disposition, and strongly influenced by the _amor patriæ_, which gave to his donations their exclusive character.
I am anxious to ascertain what was Mr. Munro's occupation in London, the date of his death, and any interesting or characteristic notes concerning him. Judging from his tastes, it seems highly probable that he may have been known to more than one of your metropolitan correspondents.
Perhaps you will not think such Queries undeserving of a corner in your useful vehicle of literary intercommunication, nor A. Z.'s _anonimity_ unworthy of an effort to rede the riddle.