may be quite sufficient to perform these two operations consecutively. The conditions would have to be very adverse to make it impossible for the tractor when running without load to secure sufficient adhesion; and the method thus helps to solve this difficult problem.

The main development in Germany prior to the war was in the direction of substantial self-contained ploughs. Some of these were of admirable design and thoroughly well built, but the general tendency was to attempt too much, which led to undue complication, and to the necessity of employing skilled mechanics in place of ordinary ploughmen.

In Great Britain, a few attempts had been made, more or less on the lines of the French cultivating method referred to above. They have not, however, been sufficiently successful to lead to anything permanent. Steady development has gone on in the direction of producing moderately light tractors for direct haulage of ploughs or other implements; and simultaneously there has been developed an essentially British type of machine which may be described as a two-furrow plough with a motor in place of a team of horses. The implement is balanced about a single pair of driving wheels, one of which runs in the furrow, and is adjustable so that the implement can cut a furrow to any desired depth and yet remain upon an even keel. These little ploughs are very handy for work in small fields and in orchards and hop gardens. They are easy to manoeuvre, and can be turned upon an exceptionally short headland. They possess natural limitations, inasmuch as, aiming at lightness so as not to compress the soil unduly, their enginepower does not suffice to work a full-sized threshing machine. In this, and also in respect of adaptability to the haulage of produce on the road, they are inferior to the independent tractor. On hilly and greasy land, they are, however, often able to operate under conditions which would make the wheels of a tractor skid and render the ploughing combination temporarily useless. This fact was well demonstrated during trials held late in 1915 by the Highland Agricultural Society, when a little self-contained plough of 10 h.p. worked well on freshly manured land involving heavy gradients, whereas in the same field comparatively heavy and

powerful tractors were unable to make any headway at all.

Other attempts to secure adhesion without undue weight are based upon the employment of endless chaintracks in place of driving wheels. This is what is sometimes known as the Caterpillar' method of propulsion. Where conditions are fairly favourable, it is probable that the chain-track method will prove less popular than the more normal type of machine, as certain complications follow inevitably upon its introduction. On the other hand, the 'Caterpillar' type can travel absolutely anywhere, and can haul a substantial load over the greasiest and roughest country. It is this method which is employed in the now notorious Tanks.'

Manufacturers of the straightforward types of agricultural tractor will, of course, point out that, to secure adhesion under adverse conditions, spikes or strakes are provided which can be attached to the driving wheels at short notice. In some instances, fittings of this kind have been devised which are no doubt fairly, if not entirely, effective. Nothing of the sort can, however, quite overcome the tendency towards skidding upon grease or upon freshly manured surfaces, which often serve to clog the strakes or spikes, so that in a few moments they become inoperative. Consequently, many farmers still regard the agricultural tractor as a dryweather machine. However, even if we admit this to be a more or less permanent limitation, it is not nearly so serious as may appear at first sight. The superior speed and power of a tractor allow the farmer to choose his time for performing various operations. In fact, one of the principal arguments for mechanical haulage upon the land is that the various jobs can be done with great rapidity when weather conditions are just right, and the yield of the land is thereby improved. This is one of the main advantages of mechanical haulage upon the land; and another allied to it is the capacity for cultivating to a greater depth than is often possible by means of horses.

Reverting to the provisions made for securing adhesion on soft ground, it is evident that spikes, strakes, or other devices likely to be effective for such a purpose would be pretty certain to damage the surface of comparatively

hard roads, and at the same time to cause injury to the tractor wheels while the machine is travelling over macadam or setts. Such fittings are of course illegal upon the public roads of this country; and it is therefore important that they should be so designed as to allow for their being removed or put into place at very short notice. It is a serious matter if, after completing the work in one small field, two or three hours have to be wasted before the tractor can cover a few hundred yards of public road with a view to entering another field. Some manufacturers have watched this point carefully; others appear to have ignored it entirely.

Agricultural tractors of the independent type ought of course to be useful not only upon the land, but also for the haulage of produce and supplies between the farm and the market or railway station. In general, they are not, however, so well suited to this class of duty as is a tractor designed primarily for road work. The efforts, quite rightly made, to keep down weight so as to avoid packing the soil often lead to the fitting of wheels which are too light to stand the vibration inseparable from road work. Moreover, springs are, in some examples, absent altogether, and in others more or less inefficient. As a result, the mechanism is subjected to severe vibration when rough and hard roads are being traversed. An agricultural tractor ought to be, so far as possible, suitable to be handled by a man with little or no mechanical knowledge or ability. It is doubtful, however, whether it is possible to design one which, while due regard is paid to the conditions of field work, will not be exposed to the risk of injury when driven at high speed upon hard roads.

As regards future development in the use of farm tractors in Great Britain, it is beyond question that the movement will increase materially even if dependence is placed solely on individual enterprise. There are, however, two ways by which it could be substantially assisted. One of these is by the more whole-hearted adoption of the cooperative principle. British farmers have been slow to accept this principle; and the best progress has been made among the small holders in Ireland. The methods adopted with the assistance of the Irish Agricultural Organisation Society are perfectly

sound. A Cooperative Society grows naturally from small beginnings, and depends for its financial success on the fact that modern methods are comparatively speaking economical. Thus, an implement owned by a Cooperative Society can be hired out to members at a rate which shows a good profit to the Society, and an appreciable saving to the members as against the cost of working with more primitive appliances. The funds of the Society thus accumulate, until it is in a position to purchase even the most expensive implements, including agricultural tractors and motor ploughs.

A second means of accelerating progress has already been briefly indicated. It consists in making arrangements for the conduct of comprehensive and conclusive experimental work at our scientific agricultural centres. This is a matter directly for the Board of Agriculture, and indirectly for the consideration of the Departments upon which that Board depends for the necessary pecuniary assistance. The Board is no doubt fully alive to the importance of popularising motor power upon farms. The Departmental Committee appointed in 1915 to consider the question of home production of food recommended that special consideration and assistance should be given to the manufacturers of agricultural motors. Moreover, at the instigation of the Board, numerous small trials were held in various parts of the country. These were of undoubted assistance in enabling farmers to form an opinion as to whether some of the machines that are now being imported are reasonably suited to their requirements. In the Oversea Dominions and Colonies there are enormous potential markets; but at the present moment, pending the appearance of some more complete programme for safeguarding the future of British industry, it is impossible to say how far our manufacturers can assume that they would be justified in producing on such a scale as to cater effectively for these markets as well as for our comparatively small, but rapidly increasing, home demand.

HORACE WYATT.

Art. 12.-AIRCRAFT POLITICS IN WAR TIME.

1. First and Final Reports of the Committee on the Administration and Command of the Royal Flying Corps, etc. Wyman, 1916.

2. Aircraft in Warfare. By F. W. Lanchester. Constable,

1916.

3. Aircraft in War and Peace. By W. A. Robson. Macmillan, 1916.

·

THE plain man is as much inclined to think aircraft politics beneath his notice as he is to consider aircraft technics above his head. He wants plenty of good aircraft and is willing to pay for it; he is reluctant to study the new-fangled troubles with which the fulfilment of this very simple desire seems to be beset. He probably recollects vaguely that his good friend Lord Derby looked in upon the arena, asked advice from Harrods' Stores,* left and was silent; that Lord Montagu also looked in and left, but was not so silent; that Lord Northcliffe offered so much advice that he thought himself obliged to disclaim the ambition of becoming First Lord of the Air.' If the plain man was little moved by these doings, he was still less impressed by the arrows of Mr Billing and the slings of Mr Joynson Hicks. It was only persons in that very narrow coterie which calls itself, and is, the aeronautical world,' who noted that these two gentlemen had the approval of Mr C. G. Grey, editor of 'The Aeroplane,' a Trade journal; and it is generally known that, outside of the Services, which have no politics, there is no aeronautical world but the Tradei.e. those who profit by the sale of aircraft and aircraft sundries or are engaged in their production or design.

About July 1916 Mr Billing and a few others were busy whistling for a wind; it was difficult to know with what exact object, but they got a hearing by timing the waves of their tumult to the various Zeppelin raids. In this way we come to the charges of using 'murderous' aeroplanes. It appears that, some time before the war,

* The Burbidge Enquiry Commission, appointed by Lord Derby in April 1916, which reported subsequently to the Air Board when under Lord Curzon.