32G 
PROFESSOR H. B. DIXON ON THE MOVEMENTS 
wave. The curious stratification of the light-giving particles behind the detonation- 
wave (observed in many of the photographs) allows this movement to be followed, and 
indicates the length of the excursion made by each layer of gas.^ When the 
detonation-wave hits the closed end of the tube it is reflected back in a distinctly 
marked luminous-wave. What is most remarkable about this reflected wave is its 
great luminosity. As the reflected wave starts back from the end wall it has at first 
to meet the gas moving bodily forward in the wake of the detonation-wave. As it 
continues backwards the gas it meets has less and less forward motion, and at a 
certain point (usually some 400 to 500 millims. from tlie reflecting end) the gas it 
travels in is stationary. From this point the motions of the reflected wave and ot 
tlie mas it travels in are in the same direction. It follows therefore that the velocitv 
O */ 
of the reflected wave is at first retarded and afterwards increased by the motion of 
tlie medium. This is probably tbe reason why the reflected wave sometimes appears 
to travel faster as it proceeds backwards along the tube, as in figs. 10, 11, and 15, and 
sometimes appears to travel at a nearly uniform velocity, as in figs. 7,8, and 9, in spite 
of the cooling by radiation and conduction going on. The elfect of these movements of 
the gas appears again in the j^hotographs taken in repeating the experiments of 
Oettixgen and Geenet (p. 348). 
The reflexion-waves can be readily photograpbed in the brighter explosions as far 
l)ack as 120 centims. (4 feet) from the reflecting end, and when the gases are fired in 
short tubes, waves that have been reflected from the ends eighteen to twenty times 
can still be pliotographed. 
Three views may l^e held in regard to these reflexion-waves :— 
(1) The combustion continues for a considerable time after the detonation-wave 
has gone by, and the returning compression-wave may owe part of its luminosity to 
increased chemical combination taking place in its path; 
(2) Tlie combustion is practically completed in a short time, and the reflected wave 
travels in the burnt gases as an intense compression-wave of the same nature as a 
sound-wave of large amplitude ; 
(3) The reflexion-wave travels as in (2) through the still combining gases without 
materially aftecting the chemical changes proceeding. 
According to the first view the continuation of the combustion may be due either 
to dissociation, which permits the gradual formation of compounds (e.ff., CO^) only as 
the gases cool down, or to the time retpiired for the natural completion of the reaction 
* In some of the photographs this stratification ajipears almost too regular to he accidental; can it he 
due to vibrations in the gas causing the dust to arrange itself in transverse streaks along a ventral 
segment, as the lycopodium arranges itself in Kuxdt’s tul>es when the length of the tube is not an exact 
multiple of the wave-length 1 - 
