168 
MINUTES OF PROCEEDINGS OF 
velocity. Hutton did the same. Turn to Didion’s Treatise, and there it is 
found that Chapter I. is devoted to the consideration of projectiles moving 
in a vacuum, but in Chapter II., when he comes to the consideration of a 
practical case, he is met by the old difficulty of the amount and law of the 
resistance of the air. He also requires to know in what way, and to what 
extent, the resistance of the air is affected by the form and size of the 
moving body. Now it is remarkable that the electro-ballistic pendulum 
should have been in such general use for more than ten years, and that no 
satisfactory attempt should have been made to confirm, or otherwise, the 
laws determined by the old ballistic pendulum for round shot, and to extend 
them to cylindrical bolts with variously-formed heads. So far as the 
comparison of the two pendulums is known to have been attempted, we 
have seen, on the authority of M. Didion, that they give a different law, and 
that he considers the results of the old ballistic pendulum the more 
satisfactory of the two. And I am the more inclined to believe that 
nothing had been attempted with success up to last year from the 
remarks made by Major Navez in his “ Considerations sur les Experiences 
de Balistique en ce qui concerne la Mesure du Temps f 1865. In that tract, 
he explains in general terms the method to be pursued in order to determine 
the resistance of the air. He recommends that the screens should be placed 
as much as 100 metres apart. He finds that M. Boulenge's chronograph 
cannot measure an interval of time exceeding 0 "'!; that of Colonel Leurs 
cannot exceed 0"’227964. He thinks it would be advantageous to have a 
superior limit of 0"*32, but contents himself with 0"*2. Major Navez 
remarks in his introduction : “ Nous avons souvent entendu, nous entendons 
encore chaque jour, des officiers d'artillerie regretter que Ton ne connaisse 
pas, d'une maniere plus precise, la veritable expression de la resistance de 
Pair quant a sa forme analytique et a sa valeur.” 1 And again, “ Jus- 
qu’a present on connait peu de chose sur la loi de la resistance que Fair 
oppose aux projectiles allonges; plus tard, lorsque des experiences com¬ 
pletes auront fait decouvrir la veritable loi de cette resistance, on trouvera 
probablement le procede dhnterpolation par arc de cercle bien imparfait. 
C’est pourquoi nous tenons a etablir quhl s'agit seulement ici d’approxi- 
mations, grossieres peut-etre, mais suffisamment approchees de la verite 
pour eclairer nos investigations.” 2 And the following remark is worthy 
of particular attention : “ Quand on examine en masse les resultats obtenus 
dans les experiences sur les vitesses conservees par nos projectiles allon¬ 
ges, a differentes distances de tir, on doit se trouver fort satisfait, en ce 
sens, que de ces resultats ressort, a ^evidence, la bonne conservation de la 
force vive, Mais si on se livre a un examen plus minutieux, on voit que ces 
resultats ne sont pas , en general , assez reguliers pour qu’on puisse les em¬ 
ployer a etahlir la loi de la resistance que Vair oppose aux nouveaux 
projectiles .” 3 The perusal of the “ Considerations ” may be strongly 
recommended to any one who wishes to understand the true state of the 
case and the difficulties that have to be overcome. I have always held, and 
still hold, that as nothing really good has been effected by the ordinary 
chronographs, so nothing can be done by them. Bather than attempt to 
1 Considerations, p. 4. 
2 Ibid. p. 17. 
3 Ibid. p. 34. 
