There is a stained-glass window in the Guildhall at Plymouth depicting the inauguration of the building by the Prince of Wales in 1874; and this is the only window I have seen in which a chimney-pot hat is represented in stained glass. The hat has come out well--the stained glass gives it all the lustre of hot-ironing. Designers of commemorative windows might brighten up their works by putting in a few such hats; and artistically this chimney-pot is every bit as good as the rectangular haloes of a thousand years before. Charlemagne had a rectangular halo in a mosaic in the Lateran: Theodora and Pope Paschal still have rectangular haloes in the mosaics in saint Praxed’s church at Rome; and the Prince of Wales would have had a rectangular halo, had he been living then. Saints and angels had round haloes, but other people had to be content with square or oblong haloes while they were alive. I do not know why this was so, or what a halo really was--whether it was a thing like a rainbow which always faces you, or whether it was a flat and rigid thing which you saw obliquely when the wearer turned aside: the Old Masters have depicted it both ways. For want of higher authority I draw my own conclusions from such things as Toto Maidalchini says: namely, that saint Cassian, being puzzled, scratched his head, and thereby put his halo all awry; or that saints Pancras and Sebastian went bathing in one of the rivers of Paradise, and then sat upon the river bank while their haloes were drying in the sun. The rectangular halo is very useful for determining dates: it shows that the fresco or mosaic was executed in the lifetime of the personage who has the halo. But mosaics often need repairing--the little glass cubes get loose and come away--and after centuries of small repairs there may not be much of the original left, even if it has not all been taken down at various times in order to repair the wall behind it. When I was in Rome in 1876 the mosaics in the apse of the Lateran were lying on the floor. One of the Canons explained to me that they were just taking down the apse and rebuilding it a little further back, as the choir did not give them space enough for ceremonial. (I thought the Canons might have been content with what had satisfied the greatest Popes; and I tried to tell him so.) When the apse had been rebuilt, the mosaics were put back in it: a creditable bit of Nineteenth Century work, but still described as Thirteenth in the guides.