wish to be assured that its price is a fair one. For, glancing across the range, we see that prices can be anything between £70 and considerably over £1000! In between, there may be a difference of as much as £100 between two models that superficially appear very similar, but are from different builders. What, the newcomer to steam may reason-ably ask, does one get for slapping down an extra hundred quid upon the counter? A few handrail knobs, a better performance, a longer life, or what, if anything? Lying upon the carpet beside me as I write are two most attractive and seductive packages of about the same size, their gleaming contents cra-dled in moulded polystyrene. One is the Mamod Steam Railway. The other is an assembly kit of the Isle of Man 0-6-OT 'Caledonia' by Lindale of Rochdale. Give them a quick shop-window glance and the reasons for the difference in price of well over £150 do not leap out and hit you in the eye. A glance does not reveal that the Lindale boiler was a lot more expensive to make, nor can it show the complicated insides of its cylinders... yet, as Stewart Browne pointed out to me, a Lindale, an Archangel, a Steam-craft, a Merlin or a Mamod can all be described equally in the terms used in the Mamod leaflet-'A design based on the styling of the old-time tank type locomotive. All metal and heavily built throughout... with solid brass fittings... Forward or reverse... variable speed control... twin double acting cylinders... safety valve... whistle operable from the cab. . .' Unless a description is thoroughly detailed, it does little to help a newcomer to decide which model will suit best both his needs and his purse.

And so the Editor thought it both wise and prudent to publish a buyers' guide to steam, the locomotives under review being very completely described in character and per-formance and refinement of construction as well as in appearance. To this end, manufac-turers and loco builders who want readers to get a full acquaintance with their products in advance are sending specimens to me for running trials on my Border Counties Railway. There we shall see how they perform with different loads in different weathers; how they handle and how much fuel they consume, with the advantages that all the tests will be conducted by the same person over the same stretch of line. An onerous duty, many would say, picturing me dren-ched by rain and baked by sun, smeared with oil and reeking of methylated spirit fuel, stumbling exhausted round the garden en-cumbered by notebook, stopwatch and other measuring devices. But in such a noble cause who would hesitate? Not I, for one, In fact, I have an idea that I shall thoroughly enjoy it.

The Principles of Steam

When I mentioned this project to my friend Dave Rowlands, he was quick to point out that many people who like and admire steam and wish to run it in their gardens nevertheless have somewhat sketchy ideas of the way it works, and possibly even sketchier notions of the contrivances used by model engineers to render it applicable to our small scales on Gauge O and Gauge l, and suggested that this preparatory article should include an anato-mical outline of the basic types of miniature steam engine. When I doubted the necessity of this, Dave, who enjoys a considerable correspondence with steam operators and would-be operators, gave sufficient instances to overcome my doubts, and clinched his argument by pointing out that with electric railways it is necessary for the model Press to go over such basic things as wiring every now and again; everything being new to some-body all the time. And a basic steam anatomy has not been published for some years. So here goes.

In general there are two main types of miniature steam loco; those fired externally and those fired internally. These differences refer to the boilers. The externally fired is the simplest kind of boiler, but it is not necessari-ly found only on simple models. It is applic-able to quite sophisticated machines and is capable when well designed of any amount of work.

It consists of a water drum, with steam connections to the cylinders) and possibly also to a lubricator. The fire is arranged outside it and below, burning methylated spirit at its own rate without the assistance of any forced draught from the exhaust. The heating surface is the lower half of the boiler within the length of the fire. The great advantage of the pot-boiler (as this type is often called) is that it generates steam at a uniform rate, standing or moving, so long as the fuel lasts, and requires no attention from a 'fireman'. The potboiler is the cheapest kind of boiler to build, but can be made quite elaborate with circulation pipes to increase the heating surface and a 'firebox' to enclose and protect the fire. Pot boilers are not normally fitted with water pumps, nor is water carried on the loco. They are refilled when the fire is out and the steam pressure gon e, either by pouring, or by vacuum through a cock on the boiler.

Internally fired boilers can be of three kinds-there are more, but we are dealing here with what is commonly met.

A type that has recently been re-introduced and achieved considerable popularity due to the easy availability of gas fuel, is the centre-flue. The centre-flue boiler has certain characteristics in common with the pot-boiler. It consists of a water drum having a fairly large diameter flue passing longitudin-ally down its lower half, just as on the very early engines on the Northumbrian colliery lines. For models, the best way to send heat along the flue is to station a gas jet at the cab end, and so we find centre-flues fired by vapourising paraffin, lighter fuel, or bottled Propane. As the gas is stored on the loco under pressure, the fire does not need forcing although it is completely enclosed. However, the heating surface of the flue is not great, and so the boilers are usually proportioned to generate steam at a low pressure from an ample evaporative surface, feeding large bore cylinders which give excellent slow running and strong haulage. Thus, the centre-flue's advantages are those of the pot-boiler, plus greater cleanliness and no unwanted heat transfer direct to the superstructure. The fire being quite out of reach, and the rate of steam production uniform, it is a very safe engine for children to operate.

The most widely used internally fired boiler is the Smithies, invented by Fred Smithies, a model engineer, in the early years of this century. It consists of an outer boiler shell having a firebox space at one end and an airtight smokebox at the other. Suspended longitudinally in the shell is a water drum, which leaves a crescent shaped section for the hot gases to pass along, from the firebox to the smokebox and chimney. The fire is a smallish one and there is insufficient space in the firebox for it to burn by' free' combustion as on a pot-boiler, so it is given forced ventilation. Initially the forcing is effected by an electric fan having a hollow spigot which inserts in the chimney. As soon as the forced draught gets to work on the fire it burns very fiercely, giving as much heat as a much bigger fire burning in the open, and steam is raised quite quickly. As soon as this is apparent, the fan is removed and a tiny steam jet called the blower and located in the smokebox directly below the chimney, is turned on. This continues the good work until the loco is set in motion, whereupon the blast of the exhaust takes over the job of urging the fire and the blower is turned off. As soon as the loco is stopped, however briefly, the blower must be brought again into action, for the fire will not burn without a forced draught; indeed, it may even dribble meths and try to burn it outside the engine. As the water drum is of relatively small capacity it is necessary to carry water on the engine, which is fitted with a pump so that the water level can be maintained; if the boiler goes dry the forced draught fails, and while this preserves

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