The Editor has previously described the principles of this system in the 'Gardener'(see p. 245), and I now allude to the question after having seen the system at work on the 4th inst., under peculiar disadvantages, on the Marquis of Salisbury's estate at Hatfield. Mr Bennet, who now has the extensive and increasing gardening establishment under his charge, had resolved to adopt this system on principles of economy, and invited a party of gentlemen interested in Horticulture to visit the apparatus on its being started into work. The result of the trial was as successful as could be expected, although this at Hatfield partook somewhat of the nature of an experiment, owing to chalk being used along with the anthracite coal instead of limestone, which latter Mr Cowan finds the best for his purpose. This is the first time chalk has been employed with Cowan's apparatus, and we must compliment the inventor on the satisfactory result obtained. The kiln at Hatfield is about 12 feet wide, and from 12 to 14 feet high, the interior being egg-shaped, and containing a solid mass of fuel 10 feet high by 6 feet in diameter in the centre or widest part.

Over this glowing mass of chalk and coal an improved saddle-boiler, designed by Mr Cowan, and manufactured by Messrs Hartley & Sugden of Halifax, is placed. The characteristics of this boiler are its increased water-way, flatter span, and consequently more heating surface than is possessed by the ordinary forms of saddle-boilers now in use. All appears to be eminently fitted to the peculiar requirements of lime-kiln heating, and at Hatfield is connected with 7000 feet of 4-inch piping, nearly all of which was fully exposed to the external atmosphere at the time of the trial. In addition to heating this quantity of piping, it is expected to reduce the cost of fuel by producing lime for use on the estate. We took occasion to examine some of the lime produced from the chalk at Hatfield, and found it to be of excellent quality and quite free from cinders, ashes, or other refuse of combustion, which some imagined would deteriorate from its value. The pipes at Hatfield are on two levels, and the upper portions naturally monopolise much of the heat at the outset; still we think, when the kiln gets thoroughly into working order, there will be no difficulty worth naming, or that would not have attended the introduction of a boiler heated by any other system.

It is a question whether 6-inch mains from the boiler would not have been better than the 4-inch pipes now used; but this may safely be left in the hands of Messrs Jas. Boyd & Sons, heating engineers, of Paisley, near Glasgow, who have supplied and fixed the pipes, and in addition have erected two new forcing-houses in a thoroughly substantial manner. Every new system is open to good-natured comment and straightforward criticism, and this we believe does more good than harm. The system appears to have special advantages, and we may briefly recapitulate these as being economy in the cost of fuel and labour, since the fire may safely be left for 12 hours without any attendance, when in fair working order. One difficulty is the length of time required to get up the heat if once the fire is allowed to get too low, but this is easily avoided if ordinary precautions are exercised. The management of the apparatus being essentially different to that of others, it follows, that any one who uses this system for the first time has many little wrinkles to learn in order to work it successfully: these once overcome, the affair appears simple enough, so far as our experience of the matter derived from our seeing the Hatfield boiler in operation extends.

In concluding this short notice we wish the system and its inventor all the success they deserve. F. W. Burbridge.