NATURAL PHILOSOPHY. 167 



it in the ordinary way, and exposed to sunlight, a beautiful black positivo 

 picture will be produced on the copper, in the course of ten minutes or a 

 quarter of an hour. 



Photograph of Bursting Shells. Mr. Skaife, an English photographist, has 

 recently succeeded in taking a stereoscopic photograph of a bursting shell, 

 during the practice firing at Woolwich. The results of the experiment he 

 thus describes, in a letter to the London Times : 



A 13-inch shell, weighing two hundred pounds, was ten seconds in travers- 

 ing the air, and fell at a distance of six hundred yards from the battery. A 

 photo-stereo was taken as the shell emerged above the smoke, showing 

 three-eighths of an inch of the projectile's track, commencing at a distance 

 of eighteen times the shell's diameter above the mortar, and Ij-inch visual 

 distance above the head of the superintending officer in front. 



But though this is, I believe, the first time a mortar shell has ever been 

 photographed in its ascending flight sufficiently intense to print from, it is 

 not that " What next ?" to which I wish to call particular attention, but the 

 likeness of the human head, which so distinctly dominates in the smoke. 

 Tliis phantom does not appear to be the result of chance, for, on repeating 

 the experiment, it is invariably reproduced at a certain phase of the smoke's 

 expansion. Further, the apparition is not^nor can it, I believe, be seen by 

 the human eye, excepting through the medium of photography, which, in its 

 highest instantaneity, appears to eternize time, by giving, at the photog- 

 rapher's will, a series of pictures of things, which have their birth, marked 

 phases of existence, and extinction, in a moment (from the 20th to the 

 20,0l)0th part of a second), much too fleeting to be noted by the naked 

 human eye. 



Subsequently, Mr. Skaife took a photo-stereograph of a 36-inch shell in 

 the course of its flight, together with a phase of the mortar's explosion, 

 which is confirmatory of what he intimates in the above letter, viz., that 

 epochs of time, inappreciable to our natural unaided organs of vision, could 

 be made evident 'to our senses by a photographic camera, as decidedly as 

 the presence of animalcule in blood or water is by a microscope. 



A gentleman well acquainted with the action of shot and shell, to whom 

 the track of the projectile and its terminus in the stereo were pointed out, 

 exclaimed, " But what stopped the ball ?" To this Mr. Skaife replies : A 

 peculiarly rapid motion given to two small (each two inches square) thin 

 pieces of baked India-rubber, by means of a trigger movement, an optical 

 illusion is produced on the transit of a projectile, which may be likened to 

 the stopping of a railway carriage by a brake. 



The first application of this optical brake is perceived in the commence- 

 ment of the shell's track on the side of the mortar. The shell then appears 

 to have gradually decreased in speed, until it has gone the length of four of 

 its diameters after the brake has been applied, when it appears finally to 

 have stopped, and that for an interval sufficiently long to admit of its por- 

 trait being photographed accurately enough to give a tolerable idea of its size 

 and shape. After which (it is assumed) the shell proceeded on its rapid 

 course for one mile and a half further, arriving at its goal not one measur- 

 able iota of time less for its having lagged by the way to coquet with the 

 photographer. And thus Mr. Skaife accounts for this seeming paradox : 

 The whole operation of putting on the optical brake to the flying projectile, 

 stopping its course, and photographing its portrait, according to data sup- 

 plied by this stereo, appears to have been done in the fiftieth part of a 



