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ON PHOTOGRAPHIC METEOROLOGY. 23% 
been possible with such systematic observations, but some particularly 
good examples of rare types of cloud have been photographed, and some 
valuable studies of lightning have been secured. So far as these latter 
have been examined they fully confirm the conclusions of this Committee 
as expressed in the reports for 1891, 1892, and 1893, which may be briefly 
summarised thus :— 
1. The reality of the narrow ribbon structure. ~ 
2. The existence of visible multiple discharges. 
3. The compound nature of many discharges. 
4, The long duration of many discharges. 
During a storm which passed over Exeter on July 22, about sunset,, 
a phenomenon was many times observed which seems to deserve further 
study. 
This was a narrow ribbon flash of somewhat long duration (1°5 to 
2°5 seconds) which broke up into a long train of sparks like the trail of a 
rocket. These sparks faded away gradually, some of them lasting for a 
second or two. 
The phenomenon does not seem to have been recorded photographically, 
but is doubtless the explanation of the beads of extra bright light shown 
on some photographs of lightning. 
It is worthy of note that the beaded discharges referred to accom- 
panied exceptionally heavy rain. This suggests that the explanation may 
be the dissociation of water and recombination of the liberated gases. 
The appreciable duration of the combustion may be due to the greater 
diffusibility of the hydrogen carrying some of it beyond the oxygen and 
thereby slackening the velocity of combination. ach dissociated drop: 
would give a ball of mixed gases in proportions exact at the centre, but 
departing more and more from exactness towards the margin, where the 
time of combustion would be correspondingly prolonged. 
The relation between the thunder-cloud and lightning has been very 
clearly visible on several occasions. The cloud has always a peculiar 
structure, which may be described as a lower cumulus disc uprising as a 
thick column in the middle, which spreads out again at perhaps twice as 
great an altitude in a more or less cirriform disc. Insuch a storm, which 
is typical, the majority of the discharges pass between the margins of the 
upper and lower discs, or from one side to the other of either disc. Such 
flashes seem to be generally of a comparatively simple type. They may 
branch or twist about or resemble the ordinary discharge of an induction 
coil or Wimshurst machine. 
These flashes are often accompanied by, or immediately followed by 
more brilliant discharges between the lower disc and the earth. This is 
the ‘impulsive rush’ of Dr. Lodge, and it is in such discharges that the 
phenomena of multiple and beaded structures are presented. They are 
analogous to the discharges between the knobs of two oppositely charged 
Leyden jars whose outer coatings are imperfectly connected. 
- No grant is asked for; but the work of the Committee cannot be 
regarded as complete until a much larger number of measurements of 
altitude have been made, and they therefore ask for reappointment. 
