In the photo-electric chronograph devised by G.J. Burch, F.R.S. (Journ. of Physiology, 18, p. 125; Electrician, 37, p.436), the rapid movements of the column of mercury in a capillary electrometer used in physiological research are recorded on a sensitive Burch. plate moving at a uniform angular velocity. The trace of the vibrating prongs of a tuning-fork of known period is also recorded on the plate, the light used being that of the electric arc. The images of the meniscus of the mercury column and of the moving fork are focused on the plate by a lens. Excellent results have been obtained with this instrument.
An important development of a branch of chronography is due to E.J. Marey (Comptes rendus, 7. août 1882, and Le Mouvement, par E.J. Marey, Paris, 1894), who employed a photographic plate for receiving successive pictures of moving objects, Marey. at definite times, when investigating the movements of animals, birds, fishes, insects, and also microscopic objects such as vorticellae. The instrument in one of its forms consisted of a camera and lens. In front of the sensitive plate and close to it a disk, pierced with radial slits, revolved at a given angular velocity, and each time a slit passed by the plate was exposed. But since, in the time of passage of the space between the slits, the object had moved by a certain amount across the field of view, a fresh impression was produced at each exposure. The object, well illuminated by sunlight, moved in front of a black background. Since the angular velocity of the disk was known, and the number of slits, the time between the successive positions of the object was also known.
Marey (La Méthode graphique, pp. 133, 142, 456), by means of pneumatic signals and a rotating cylinder covered with smoked glazed paper, measured the time of the movements of the limbs of animals. The instrument consists of a recording cylinder rotated at a uniform angular velocity by clockwork controlled by a fan governor, and pneumatic signal, constructed thus. One end of a closed shallow cylinder, about 4 cm. dia., is furnished with a stretched rubber membrane. A light lever, moving about an axis near the edge of the cylinder, is attached to the centre of the membrane by a short rod, its free end moving as the membrane is distended. The cylinder is connected by a flexible tube with a similar cylinder and membrane, but without a lever, which is attached to that part of the body of the animal the movement of which is under investigation. The system is full of air, so that when the membrane attached to the animal is compressed, the membrane which moves the lever is distended and the lever moved. Its end, which carries a scribing point, marks the smoked paper on the rotating cylinder. The pneumatic signal is called by Marey “tambour à levier.”
References to Chronographic Methods:—(1) Chronographs used in Physiology: Helmholtz, “On Methods of measuring very small Portions of Time,” Phil. Mag. (1853), 6; Id., Verhandlungen der physikalisch-medicinischen Gesellschaft in Würzburg (1872); Harless, “Das Attwood’sche Myographion,” Abhandlungen der k. bayerischen Akademie der Wissenschaften (1862); Id., Fall-Myographion aufgestellt in der Wiener Weltausstellung in der Abteilung für das Unterrichtswesen von Ungarn (Budapest, 1873); Hensen, “Myographion mit vibratorischer Bewegung,” Arbeiten aus dem Kieler physiol. Instit. (1868); Brücke, Sitzungsber. d Wien. Acad. (1877); Pflüger, “Myographion ohne Bewegung,” Untersuchungen über die Physiologie des Electrotonus (1859); Pouillet, Compt. rend. (1844); I. Munk, Physiologie des Menschen (for Pflüger’s cylinder governed by conical pendulum); J.G. M’Kendrick, Life in Motion (1892) (for early form of cylinder chronograph by Thomas Young); Stirling, Outlines of Practical Physiology (for reaction-time chronographs of F. Galton and Exner). (2) Chronographs used in gun work and for other purposes: Sabine, Phil. Mag. (1876); Moisson, Notice sur la chronographie système Schultz (Paris, 1875); Paul la Cour, La Roue phonique (Copenhagen, 1878); Mach, “Collected Papers on Chronographs,” Nature, 42, p. 250; C.V. Boys, “Bullets photographed in Flight,” Nature, 47, p. 415; Pneumatic Tube Co., Paris, “Chronograph,” Nature, 9, p. 105; G.C. Foster, “Laboratory Chronograph,” Nature, 13, p. 139; E.S. Holden, “Astronomical Chronograph,” Nature, 26, p. 368; D’Arsonval, La Lumière électrique (1887); Dunn, “The Photo-retardograph,” Journal United States Artillery, 8, p. 29; E.J. Marey, La Méthode graphique (for Deprez accélérographe); Werner Siemens, “Electric Spark Chronograph,” Wied. Ann. (1845), 66.
(F. J. J. -S.)
[1] The velocity of the projectile is found thus. Let V be the velocity of the bob, due to the impact of the projectile, v the velocity of the projectile, h the height through which the bob is raised vertically, then
| h = | V² | , and V = √2gh. |
| 2g |
If W be the weight of the bob, and w the weight of the projectile, then
| wv = (W + w)V, and v = ( | W | + 1) √2gh. |
| w |