For some investigations, readily distinguishable in the plates, "_portable_" backgrounds are used, consisting of frames 3 metres wide by 4 metres high,--about 10 feet by 13 feet 4 inches,--over some of which black cloth and over others white cloth is stretched, all being divided by vertical and horizontal lines into square spaces of the same description as those of the lateral background. These portable backgrounds are used when photographing birds and horses, and also wild animals when possible to do so. L. A lateral battery of 24 automatic electro-photographic cameras, arranged parallel with the line of progressive motion, and usually placed therefrom about 15 metres or 49 feet. Slow movements are usually photographed with lenses of 3 inches diameter and 15 inches equivalent focus; the centres of the lenses being 15 centimetres, or about 6 inches, apart. Rapid movements are usually photographed with a _portable_ battery of cameras and smaller lenses. The centre, between lenses 6 and 7, is opposite the centre of the track T. For illustrations comprising both "Laterals" and "Foreshortenings," cameras 1 to 12 only are used. When "Laterals" alone are required, cameras 13 to 24 are connected with the system and used in their regular sequence. R. A portable battery of 12 automatic electro-photographic cameras, the lenses of which are 1¼ inches diameter and 5 inches equivalent focus; the lenses are arranged 7½ centimetres, or about 3 inches, from their centres. When the battery is used vertically, lens 6 is usually on the same horizontal plane as the lenses of the lateral battery. In the diagram this battery is arranged _vertically_ for a series of "Rear Foreshortenings," the points of view being at an angle of 90 degrees from the lateral battery. F. A battery of 12 automatic electro-photographic cameras, similar to that placed at R, arranged horizontally for "Front Foreshortenings," the points of view averaging an angle of 60 degrees from the lateral battery. O. The position of the operator; the electric batteries; the chronograph for recording the intervals of time between each successive exposure; the motor for completing the successive electric circuits, and other apparatus connected with the investigation. T T. The track parallel with the lateral battery and covered with corrugated rubber flooring. M. The model, approaching the point number "1" on the track where the series of photographic illustrations will commence.