equipment which comprises a projector of about 90 em. diameter, mounted on a specially designed motor car chassis. The car carries five men in addition to the projector, generator, etc. The projector is mounted on small rubber-tired wheels and is carried on the rear platform of the car, which is driven by an 30-horsepower motor and can attain a speed of 15 miles per hour. It is said to be adapted for travelling across country, and to be superior in point of speed and compactness to any previous plant of this kind. One of these searchlight cars is illustrated in Fig. 1.

The Austrians have searchlight sections consisting of a 90 cm. projector mounted on a 4-horse truck, engine and generator on a 6-horse truck and a 4-horse supply wagon. The personnel of each section includes the light commander, 1 engineer with helper, 1 projector operator with helper, 1 observer, 3 telephone operators, 1 control operator, 1 wagon-master, and 7 drivers. They also have 35 cm. searchlight sections organized on similar lines.

The Spanish used field searchlights very effectively in the Melilla campaign of 1909 against the Moors. These lights were assigned to the balloon company and comprised three 90 cm. projectors with steam-engine driven generators, one 90 cm. projector with petrol motor, one 60 cm. and one 45 cm. projector with steam engines and twelve 40 cm. projectors of the oxy-acetylene type. General Don Jose Marva, of the Spanish engineers, says that on this, the first occasion on which searchlights were used in the field in the Spanish army, they met with brilliant success and that experience has justified their employment.

The Japanese equipment used in the Russo-Japanese War is described by Maj. J. E. Kuhn, Corps of Engineers, in his report on the siege of Port Arthur. They used two trucks, one carrying the 90 cm. electrically controlled projector, the other the oil-motor driven generator, switchboard, radiator, etc.

The Italians recognized at an early date the utility of field searchlights, and had regularly organized trains at least as early as 1900. They adopted steam as their motive power, and used 36-inch and 24-inch projectors in their heavy and light trains, respectively. Their vehicles were excessively heavy, the engine and generator wagon of the heavy train weighing about 9,000 pounds. In their 1909 maneuvers the Italians experimented with a motor car carrying a dynamo and hauling a 2-wheel limber carrying the projector. The projector was said to have a limiting range of 2,500 meters.

The Dutch outfit consists of a projector wagon and a self-pro

pelled dynamo vehicle with benzine motor. The projector is of the 60 cm. size and is hand controlled.

In this country the first portable searchlight outfit to be devised was the steam-engine operated plant which was purchased about 1900 and is now at Fort Leavenworth, Kans. This set was too cumbersome to be adapted for field work, but sufficient experience was had with it to indicate the desirability of an outfit which could be readily transported. Another steam set with an 18-inch projector was designed for the Signal Corps, but was too heavy for field transportation. More recently the Navy has purchased some

Fig. 1. French Automol ile Searchlight Equipment

sets, for use at advanced bases, which are more satisfactory. They have 30-inch projectors, the current for which is supplied by a 2-cylinder gasoline engine driving a 7-kilowatt D. C. generator. The generator truck, carrying engine, generator, switchboard, radiator, gasoline and water tanks, and projector rheostats, weighs 4,040 pounds with tanks empty. The gasoline tank has a capacity of 21 gallons and the water tank of 12 gallons. The searchlight truck carries a 30-inch hand-controlled projector, cable reel with 1,000 feet of twin conductor, 75,000 cm. ; tool box, spare parts, etc., and weighs 3,720 pounds.

The Coast Artillery has also experimented with portable equip

ments. Their plants were constructed along the same general lines as those of the Navy, but had a 3-cylinder instead of a 2-cylinder engine and a device for elevating the light. The generator truck weighed 5,930 pounds, and the searchlight truck 5,400 pounds.

The most recent portable outfits designed in this country are the auto searchlight truck and the Field Artillery set, both designed under the supervision of and purchased by the Engineer Department. The former is so different from anything which has been heretofore developed, either in this country or abroad, that a detailed description of its development will be of interest.

AUTO-SEARCHLIGHT CAR

In developing special apparatus for Army uses one must look toward the existing commercial apparatus for types and ideas. Such was the case in developing an automobile searchlight equipment for our Army. The field, to say the least, was very limited, and none of the touring car manufacturers wanted to undertake special apparatus in their overcrowded factories, and, furthermore, would not undertake the production of any car when cross-country, muddy road guarantees were demanded. The development therefore tended toward heavy trucks. Of these, the choice lay between electric and gasoline motors. Since the accepted type of highpower searchlight required the supply of direct current at constant voltage, it seemed simple enough to conclude that a gasoline-electric truck would do the work. In theory the answer was very simple indeed, but when it came to the point of manufacturing such an outfit it was very difficult to obtain any electric-truck manufacturer who would undertake the problem.

About this time (winter of 1907) the writer (Wheeler) happened to run across an article in one of the technical magazines describing a gasoline electric-truck which was built especially for the work of hauling large lenses to the Carnegie Solar Observatory in Cali

This truck was built by the Couple-Gear Freight-Wheel Company of Grand Rapids, Mich., and was a 4-wheel drive, 4-wheel steer "Couple-Gear" electric-truck depending on a gasoline engine (automobile type) generating set for its current. This, then, was a plan to work upon, as it was confidently believed that a truck that could cope with the severe conditions of load and roadbed described would be eminently satisfactory for field purposes in the Army. Roughly speaking, the tests of the present machine (autosearchlight) have proven that this belief was justified.

The auto-searchlight consists of two units, the automobile, hereafter called the car, and the searchlight trailer. This outfit is shown in train in Fig. 2. The car is a specially designed and built "Couple-Gear" truck upon which is mounted a 15-kilowatt gasoline-engine generating set, the engine being of the semi-automobile type. The searchlight trailer consists of a standard Field Artillery caisson upon which is mounted a spring-supported platform, three-point suspension, carrying a 30-inch General Electric white metal mirror, electric-control searchlight with 500 feet each of supply and controller cable. Its weight, complete, is 4,400 pounds.

THE CAR

The driving system consists of four "Couple-Gear" wheels, as shown in Figs. 3 and 4. Each wheel motor is of the direct-current series railway type, of 3 horsepower capacity, normal rating, and designed for normal operation on 85 volts, although they have satisfactorily operated without any perceptible sparking on 150 volts. The motor is of the pancake type and bi-polar. The back frame is a part of the inside support which is connected to the rigid axle through the steering knuckle. The motor armature has a shaft running through it, on each end of which is a bearing which is part of the motor casing, and a bevel pinion. One pinion engages in a circular bevel rack which is a part of the outer disk of the wheel. while the other pinion engages in a similar rack which forms part of the inner disk. This construction gives the wheel the name "Couple-Gear," since a couple of forces is acting to turn the wheel around the motor, the forces being applied practically at its rim. There is located in the armature shaft an evener," a device which allows the same amount of power to be transmitted to each pinion. This device is simply a compound knuckle coupling, and is believed to be responsible for the satisfactory operation of the wheel: first, because it removes practically all sliding friction on the gear teeth, thereby increasing greatly the life of the pinions, and, second, because it insures the transmission of equal amounts of power to each side of the wheel, thereby increasing the efficiency and maintaining a true couple.

The efficiency of the gear-drive is remarkable, there being less than 3 per cent loss in the "Couple-Gear" drive. In Appendix A, is submitted a report of the National Bureau of Standards' test on the right front wheel of this car.