PROFESSOR IT. B. DTXOX OX THE .MOYEMEXTS 
;U8 
stretched Ijy weights and rendered Inminons hy an electric current. If a second wire 
is l)rought to touch the first so as to divide the current, the portion of the wire which 
carries the whole current is more luminous than the other portion, and the photo¬ 
graphs make it appear of far greater diameter. Fig. 73 is a j)hotograph taken in 
this way, with the same camera and films as were employed for the explosions. If 
the effect in tire explosions is due to halation, we ought never to see the bright line 
displaced so much as not to overlap the duller line on hoth sides. Xone of our 
photographs show such a displacement, the effect might therefore he caused by 
halation alone. 
We may thus summarise the evidence against the existence of Le Chateliee’s 
“ inrusible wave ” :— 
1 . Its supposed effect is onl}^ seen when the contrasts are strong, and not on 
photographs of the same phenomena in which the contrasts are not brought out. 
2 . It can he imitated in various ways by means of contrasts. 
3. The same effect is seen in the collision of two detonation-waves, but Le Chateliee' 
does not suppose that the “ invisible wave ” can precede the detonation. 
2 . Repetition of x. (dEXTiXGEX and v. Geexet's Experiments. 
The very short time required for the explosion in electrolytic gas to raise the 
Welshach oxides to incandescence (as shown in figs. 70 and 71) was strong evidence 
against the view held by v. Oettixgex and v. Geexet, viz. : that the detonation of 
electrolytic gas is invisible, and that the salts jDresent in their experiments only 
became luminous after the combustion had been for some time complete. Our 
previous experiments had also shown conclusively that the detonation is not set up 
at once, but only after the flame has run some distance, which varies with the nature 
of the mixture and the position of the spark. But to place the matter beyond 
all doubt we have repeated their experiments, using a tube of the same size and 
construction as theirs, filled with electrolytic gas, but without the addition of any 
salts. By careful development, the course of the fiame can be seen on the negatives 
from the firing wire. In all cases the explosion begins slowly, and has slight 
luminosity until the retonatioir-waves are started hy reflexion from the ends of the 
tidae. 
In fig. 74 the explosion was started in the centre of the tube (400 millims. long). 
Just as in v. Oettix’GEx’s “ fig. 8 ” (our fig. 5, Plate 10 ), a line of light joins the spark to 
the more luminous portion of the explosion ; but instead of a detonation-wave travelling 
three and a half times the length of the tube before the first visible compression-wave 
descends from the top of the tube (as in tlieir explanation), the flame is seen to travel 
slowlv right and left until it meets with the return sound-wave from the end of the 
tube. The flame is checked while these two sound-waves cross the ignited ga.ses, 
