APPENDIX. THE STROBOSCOPIC METHOD.* By means of this method all kinds of motion which exactly repeat themselves can, whatever their rapidity of occurrence, be rendered visible, as if taking place slowly. Suppose any object to be illumined by flashes of light: owing to the power which the retina possesses of retaining sensation, if these flashes recur within a certain fraction of a second of each other, the body appears continuously visible; this will be the case even if it moves in the interval, and, if its movement has been a complete vibration, it will appear stationary; if, however, it happens not to have returned quite to its original position, or to have returned and commenced another excursion, by the time the next flash of light occurs, it will appear to have moved from its first position to another, and so on; indeed the body may make any number of vibrations between the successive flashes of light, and yet only appear to have moved that small distance which consists of the difference of its positions under the consecutive flashes. Since the same holds good at any part of the course of the body, it is evident that it will be seen to go through its whole vibration, but less quickly than it actually does, and, moreover, that by a suitable adjustment of the times of the flashes, any * "Die Spectrale und Strobscopische Untersuchung Tonenden Korper. E. Mach. Prag.," 1873. Abstract by Lucae, in "Archiv für Ohrenheilkunde," 1873. degree of apparent slowness may be attained-limited only by the inability of the retina to retain sensations of light for more than 5 of a second; for if the next flash does not occur before the effect of the first becomes faint, the object will seem to be flickering, or to start up in different positions. Let us take the case in which there are ten flashes of light to eleven vibrations of the body: at each successive flash the body is seen one-tenth of its whole vibration further on. In this way at the first flash the body is one-tenth of its way on its vibration, at the second, two-tenths, and so by the tenth a whole vibration has been displayed. Brenner, Dr., 251 Brown-Séquard, 19, 70 Bubbles on the membrane, 35 Bulging of membrane, 151 CATARRH of tympanum, 127 Children, disease of ear in, 49 Cochlea, 17 Cold, effect of, 136 Colours perceived from sound, 21 Consonants, 11 Convulsions, 68 Cough, 76 DALBY, Mr., 244 Deaf-mutism, 230, 276, 230 Down, Dr., 231 EARACHE in children, 221, 269 Eczema of meatus, 76 Electricity, 250 Emphysema of pharynx, 110 Epidermis, collections of, 80 Epilepsy, connection of deafness with, 280 epidermis in, 33 Hart, E., 19 Hearing in a noise, 21 improved after hemiplegia, 20 shortly before death, 20 returning suddenly, 980 Helmholz, 6, 15 foreign bodies in, 72 form of, 23 gout of, 93 inflammation of, 90 --affecting bone, 233 Membrana tympani, adherent to tympanic wall, 203 appearance of, 25 bright spot, 25 collapse of, 37 cretaceous deposit in, 120 curvature of, 29 injuries of, 121 perforation of, 173 thinner spots of, 34 with effect of quinine, 288 Mucus, accumulation of, 138 causing irritation, 142, 158, 162 Mucous membrane of tympanum, proliferous inflammation (scle- SCARS of the membrane, 179 moving with respiration, 31 appearances due to, 31 Stroboscopic method, 303 Suppuration in tympanum, 127 |