Mae'r llythyr hwn yn adrodd hanes tân ar fferm Nantmawr, ger Llanrwst, ym 1824. Cafodd y tân ei gynnau'n ddamweiniol gan un o'r morwynion a oedd yn cario cannwyll frwyn. Ymledodd y tân yn gyflym gan achosi difrod mawr i'r adeiladau a'r stoc: llosgwyd 21 o'r gwartheg a difrodwyd ymron y cyfan o'r barlys a'r gwellt. Ysgrifennwyd y llythyr hwn at y perchennog tir, Arglwydd Newborough, gan E. Owen, Melai, ar ran y tenant. Gofynnodd iddo ystyried sefyllfa ariannol y tenant yn ofalus a thrugarhau wrtho pan fyddai'r taliad rhent nesaf yn ddyledus. Adysgrif o'r llythyr:

'Dear Sir,
It is with much concern I inform you of the Afflicting event that happened at Nantmawr last Friday night after the family retired to bed except the two servant women, the youngest of them went to a bing[?] before the cattle with a rush candle in her hand to fetch a little straw to light fire the next morning and as I find by her holding the candle in a careless manner the straw took fire and entered into a great Quantity of straw which was above the cow houses - it is supposed that she tried to put it out - untill the other woman gave the alarm, by that time the fire raged so violently, that out of 22 head of cattle only 5 could be brought out and those very much burnt except one - the horses were in the adjoining stable they saved them with much difficulty but the gears[?] are all destroyed, the Barn comes next in which they had upwards of 20 hobbets of barley some in sacks and the rest unwinnowed only 3 or 4 sacks were saved. A large stack of hay at the back of the building was entirely consumed, and also two stacks of Barley supposed to be about 30 hobbets which was all the barley they had - They were very fearfull ...'