THE EOYAL ARTILLERY INSTITUTION. 
223 
The means are generally of six records, and the mean error of a single 
observation varies between one division and three divisions, according to the 
observer. On the whole, it is about 1*66 divisions, or O'0015 second—a large 
quantity compared with the precision since attained; but we* are discussing 
the infancy of the subject, when it was regarded as very close observation. 
It would be foreign to the subject of the present paper to enter into any of 
the controversies to which the invention of the chronoscope gave rise. A 
single extract from a declaration of Lieut.-General Konstantinoff, dated 
July 11, 1847, may be given, to show that the genius of our countryman 
was not long in finding appreciation among scientific officers abroad :—- 
ct En 1842 M. Wheatstone me livra un appareil de son invention pour mesurer 
le temps du mouvement d’un. projectile entre deux points de la trajectoire. 
C’etait un appareil a echappement pouvant etre rendu dependant du mouvement 
d’un projectile par l’effet d’un electro-aimant faisant partie de l’appareil et de 
courants voltaiques. Ce fut le premier appareil base sur l’application des electro* 
aimants dont je me servis dans mes recherches balistiques que d’abord n’eurent 
pour but que la determination empirique de la loi de la resistance de l’air.’* 
The rest of the paper—which is a vindication of the priority of Sir 
C. Wheatstone against M. Breguet, of Paris, who had been subsequently 
employed by Konstantinoff to make him an apparatus—is scarcely connected 
with our subject, and I proceed with the experiments of the 36-inch mortar. 
29. The slow and majestic motion of these great globes through the air, 
suggested irresistably to all who witnessed it the possibility of laying down 
their trajectory in some graphical manner. Accordingly, on the 18th 
December, Mr. Cooke, Secretary to the London Photographic Society, 
attended with his camera, and made several attempts. The weather was 
most unfavourable for the purpose—the temperature low, the light dull; 
but he succeeded partially with one shell during a momentary gleam of 
bright sunlight, as it was passing across a patch of clear sky. The impres¬ 
sion was extremely faint, and of no practical value, but it encouraged a belief 
that, under more favourable circumstances and with apparatus specially 
prepared, the thing would be feasible. The same gentleman tried another 
method with better success. He divided the ground-glass plate of the camera 
into squares, and with the point of a fine pencil tried to follow the path of 
the shelb In this manner two foreshortened curves were obtained, nowhere 
(as was thought) more than two diameters of the shell in error. The camera 
was considerably behind the mortar, but if its place had been exactly central 
and perpendicular to the plane of the trajectory, it seems probable that real 
representations of it might have been obtained, although it would have 
required much greater quickness of eye and hand. These experiments were 
but preliminary, and are an example of the many highly interesting enquiries 
which were cut short by the decision of the Secretary of State not to repair 
the mortar.* 
30. On comparing the ranges in Table IV., where the charges are 
expressed in terms of the weight of the shell with those of the 13-inch land- 
* A sort of open-air screen of larger squares mounted on a stand, was also prepared, on Mr. 
Mallet’s suggestion, but I believe not tried. 
30 
