276 Retrospective Criticism, 



birds built in the same tree, of their own choice. It was a large beech, and 

 in a cleft near its top the rooks had accumulated a quantity of nests, while 

 several jackdaws had taken possession of the lower part, and there reared 

 their young. This double colony on the same tree had a most singular ap- 

 pearance. Mr. Waterton says that, perhaps, there is no instance on record 

 of the jackdaw ever building its nest, hke the rook, in the open air. I knew, 

 however, of such an instance, which occurred in the place already mentioned. 

 The Earl of Leven had some work done at his mansion, which drove the 

 jackdaws to build their nests in rabbits' burrows, and on spruce fir trees. 

 The jackdaw showed but little sagacity or contrivance, when reduced to build 

 on these trees ; but, as in the house, piled up a vast quantity of materials very 

 loosely together. The trees where the Jackdaws built grew in a thick |)lant- 

 ation, and I well remember the joy I felt with other boys of my age, when we 

 discovered jackdaws instead of rooks. — John Wigliton. Cossei/ Hall Gardens, 

 Feb. 12. 1840. 



Joyce's Stove is made up of two concentric cylinders, the inner one being 

 the furnace part ; it gives out more heat from a given quantity of fuel than 

 any other stove with which I am acquainted. From this stove I borrowed 

 the idea which led me into the error which is kindly corrected by W. of 

 Darlington at page 227. Mr. Rogers also pointed out to me, in a private 

 letter, Ihe error into which I had fallen. I am obliged to both gentlemen for 

 their leniency, and I consider that I was fortunate in falling into such respect- 

 able hands. 



I wish Mr. Rogers had given as full directions for mixing and using the 

 cement with which the joints of the pipes are made, as he has given for 

 putting up and managing his boiler. This would enable every gardener in 

 the country to put up the apparatus with the assistance of a blacksmith. 

 I ought to know all this, having superintended the making of very many 

 joints for the last ten years ; but I quite forget the proportions now, and I 

 mix all my cement by guess. 



In fixing the pipes for any close boiler, the first length, and sometimes the 

 first two lengths, of the top pipe are placed higher than the boiler, in order 

 to prevent a vacuum in the top of the boiler, where steam would soon gene- 

 rate. In the old close boilers of large dimensions, I used to rest satisfied if 

 the top pipe were a few inches above the boiler ; but, as the highest part of the 

 pipes in all cases may be considered in effect to be the top of the boiler, 

 perhaps the higher the pipes are placed above the conical boiler they may 

 give a proportionate capacity to it, and thus account for the disproportionate 

 height of the pipes recommended by Mr. Rogers. 



A small iron pipe, 5 or 6 inches long, and an inch or half an inch in dia- 

 meter, fixed upright in the highest part of the top pipe, is more simple than 

 an air-cock, and answers just as well for letting the air out of the pipes, and 

 allowing the water to expand. From this point the top pipe should dip 

 towards the farthest end, if only 1 in. in 50 ft., and the under pipe should 

 incline back all the way to the bottom of the boiler. I dishke elbow turns 

 at the end of the pipes for many reasons ; and I should always have a cistern 

 there when practicable, if ever so small, with a close lid to it. This cistern 

 is the proper place to supply the pipes with cold water when the boiler is 

 at work, and if a small pipe could be conveyed to it from a rain-water butt 

 or cistern, with a ball-cock, it would be the handiest thing in the world. 

 I never like to add cold water to a boiler at work, and I do not think it 

 is right to do so. During the growing season of plants, I should keep the 

 cistern open to discharge its vapour into the house or pit, and when it was 

 desirable to have a dry atmosphere for ripening off grapes, pines, and other 

 fruits, the lid should be kept constantly on. 



If Mr. Penn would use small cisterns in his system, and have them so 

 arranged, that one cistern would come in at the centre of each of his air 

 drains, it would be a considerable improvement ; there would not be any 

 necessity then for chilling the air of the house by throwing down cold water 



