THE ROYAL ARTILLERY INSTITUTION. 
165 
This asserted maximum is in itself very improbable, and M. Didion 1 2 
declares that there is none deducible from Hutton's experiments. Hutton's 
attempt to account for this supposed maximum, by reference to the velocity 
with which air rushes, into a vacuum, is extremely fanciful—because the 
after-pressure is not great to begin w r ith, it diminishes rapidly as the 
velocity is increased, but perhaps never entirely vanishes. 
Professor Wheatstone applied electricity to measure the velocities of shot 
in 1840. Afterwards, several changes were made in his instrument. 
Drawings were shewn in Paris, in May, 1841, and a copy was prepared for 
Colonel Konstantinoff; but he desired to have an instrument by which he 
could determine the velocity of a shot at different points of its path? 
M. Breguet afterwards constructed an instrument for this purpose, the 
performance of which will be further noticed hereafter. This led to a 
dispute between Professor Wheatstone and M. Breguet, respecting their 
claims to the invention of the chronograph. 3 Pouillet attempted to 
determine short intervals of time on the supposition that the deflection of a 
magnet needle is proportional to the strength of a galvanic current, and to 
the time it is acted upon by the current. Hipp objected to Professor 
Wheatstone's arrangement, and made use of a clock going uniformly to 
measure his time. It does not appear that any of these chronographs have 
come into use, or that they have given results of any importance. 
The electro-ballistic pendulum of Major Navez was invented about 1848, 
but was brought prominently into notice only in 1855. Yery various 
opinions have been expressed respecting the value of this instrument. The 
Americans tried it and rejected it on account of the irregularity of its 
indications* The Prench used it in 1856, 1857, and 1858, at Metz, to 
complete their researches on the resistance of the air. “ Les resultats n'ont 
pas ete formules, ils font voir qu'aux vitesses moyennes la valeur de p est 
egale a celle qui a deja ete donnee, mais que pour des vitesses plus pefcites 
la resistance diminuerait heaucoup plus rapidement que par la formule deja 
obtenue (Art. 52, eq. 7), et qu'elle decroitrait meme trop rapidement pour 
etre des maintenant admise". 4 Experiments with small arms were 
continued in 1857 and 1858, with new precautions, on which M. Didion 
observes: “ Elies ont presente, comme les precedentes, une diminution trop 
rapide dans les valeurs de p r , et les resultats n 9 out pas donne une formule 
qu 9 on puisse appliquer au tir avec une entiere confiance " 4 . Others who 
have used the instrument have expressed a very high opinion of its accuracy. 
It is undoubtedly a great improvement upon all instruments that preceded it 
for rough practical work, but it is wanting in that precision we are entitled 
to ask for when electricity is brought to our assistance. It may well be 
doubted whether anything has been contributed to our knowledge of the 
laws of the resistance of the air by Major Navez's electro-ballistic pendulum, 
or by the modifications of it by De Brettes, Yignotti, Leurs, &c. In 1861, 
it is plain that M. Didion gave the preference to the results of the old 
ballistic pendulum. 
1 Didion, Traite, p. 64,1861. 
2 Muller, Berichte, p. 856, 1848. 
3 Moigno, Traitd de t&egraphie dlectriqne. 
4 Didion, Traite, 1861, p. 71. 
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