66 
PROF. H. A. WILSON ON THE ELECTRICAL CONDUCTIVITY AND 
above. A brass tube, TT 7 , about 3 cm. in diameter and 15 cm. long was soldered 
to a base plate, B. At D and D' brass disks were fitted tightly into the tube, TT'. 
Each of these disks had seven holes bored in it as shown in fig. 2, and seven 
parallel brass tubes connected the holes in the lower disk, D', with the holes in 
the upper disk, D. The mixture of gas and air entered through the side tube, G. 
The flame had seven sharply defined inner cones. The upper part of the burner 
was surrounded by a brass tube, A A 7 , about 4'5 cm. in diameter, supported by 
three small brass blocks not shown in the figure. 
A grating formed of ten platinum wires was fixed across the tube, AA 7 . about 
one millimetre from its upper end. This grating 
was heated bright red hot by the flame and 
formed one of the electrodes. A mixture of air 
and spray of a salt solution entered the burner 
through a second side tube, H, which led into the 
space between the seven tubes. This mixture 
entered the flame through a small hole, S, in 
the upper disk, 1), and produced a streak of salt 
vapour extending from S to the top of the flame. 
The air and spray entered H through a stop-cock 
which was rapidly opened and closed by means 
of an electric motor. The streak of vapour was 
therefore not continuous, but consisted of a series 
of puffs of vapour moving up the flame. The 
amount of salt in each puff could be varied by 
adjusting the pressure of the supply of air and 
spray. It could be diminished till the puffs were 
only just visible or increased till they were 
intensely luminous. 
The shaft of the motor carried a disk having 
four equidistant openings near its circumference. 
The stop-cock was opened four times during each 
revolution of the motor. The flame could be 
observed through the rotating disk so that it was then seen as many times per 
second as the stop-cock was opened. The puffs of salt vapour were then seen in 
the flame apparently stationary in a series of nearly equidistant positions one above 
the other. Fig. 3 shows the apparatus used. B is the burner and FF 7 the flame. 
S is the stop-cock through which the air and spray entered, and DD 7 the rotating 
disk carried by the motor shaft, M. AA 7 is a wooden base covered with a sheet 
of asbestos, TT 7 . GG 7 is a glass cylinder resting on the wooden base. The top of 
the cylinder is covered by a brass plate in the centre of which is fixed a vertical 
brass tube. C, which, with a tube, C 7 , formed a chimney up which the gases from 
M 
