108 ANNUAL OF SCIENTIFIC DISCOVERY. 



second. The shell, at this part of its course, is supposed to be flying at the 

 rate of 500 feet per second (the diameter of the shell is believed to be about 

 two and a half feet), when the now applied brake gradually retards its 

 flight, and finally succeeds in stopping the shell after it has gone four diame- 

 ters, or ten feet, from the first application of the brake. The commence- 

 ment of the shell's track on the side of the mortar, it will be perceived, is 

 misty and ill-defined ; while, on the contrary, the termination is sharp, and 

 gives a tolerably clear idea, of the sort of snail that has been leaving its trail 

 behind. This difference between the beginning and end of this photo- 

 graphed section of the projectile's parabola is thus accounted for: The 

 vulcanite " spring shutters " admitted to the sensitized collodionized plate, 

 through a pair of lenses, a yiew of the shell the instant it emerged from the 

 mortar's smoke, by being made to revolve on their axis ninety degrees, at 

 which point they have exposed the full aperture of the lenses, and at this 

 point the 100th part of a second has elapsed. Meanwhile the shell, flying 

 at the rate of 500 feet per second, has just interposed its trail on the collo- 

 dionized plate, the length of two of its diameters (one-eighth inch), and suc- 

 ceeds in trailing two others while the shutters are having their action 

 reversed and returned to their original light-excluding position, behind the 

 lenses. Now, as the first part of the shell's track (one-sixteenth of an inch 

 wide) has been exposed to the full action of light from "the commencement 

 of the shutters' opening to their final closing, this part of it has consequently 

 been undergoing a gradual effacement during the whole period of the fiftieth 

 part of a second; while, on the contrary, the terminus of the track photo- 

 graphed at the final closing of the shutters, must, in the shortness of its 

 exposure to the action of light, bear a moring analogy to the rapidity of 

 light itself, known to travel more than one million of times quicker than a 

 cannon ball. And hence the ball's apparent stoppage in the air malgre the 

 tremendous physical force argument seen in the act of urging it forward. 



BALLOONS AND PHOTOGRAPHY APPLIED TO MILITARY PURPOSES. 



It is well known that among the many novelties introduced into the service 

 of war by the French Emperor, is that of the use of balloons; by means of 

 which, " wherever the general goes, he has at his command a tower of great 

 altitude, whence to contemplate all the surrounding country." This employ- 

 ment of balloons was often talked of even in the time of Napoleon I., but it 

 was left to Napoleon III. to render it a reality. In order that the project 

 might be fairly tested, the Emperor summoned to Italy M. Goddard, the 

 most eminent of the French aeronautists, and the consequence has been a 

 marked success. The balloon ascends to the height of screral hundred 

 metres, and is held down by cords whilst an officer makes his observations. 

 Very important information respecting the disposition of the Austrian army 

 is said to have been so obtained prior to the battle of Solferino. But we now 

 learn from the Photographic News that the Emperor is anxious to employ 

 photography in these balloon observations. Some months ago, M. Nadar, a 

 distinguished photographer, made an ascent from the Hippodrome at Paris, 

 in order to make experiments in taking photographs at different altitudes. 



We also learn, from the same source, that M. Porro, who has invented an 

 apparatus, by means of which it is possible " to take a panorama rigorously 

 exact of the whole horizon, in three proofs, by an operation that can be ac- 

 complished in a few minutes," has been taken into the service of the Pied- 



