574 
NATURE 
[OcroseR 12, 1899 
A close examination of the figure shows that, not only 
do we get types of simple bright flashes, but we obtain 
dark flashes with bright cores and bright flashes with 
dark boundaries. 
Now A (Fig. 6) is exactly similar in type to the dark 
flash in Fig. 4, A, while the two bright flashes in C corre- 
spond also to the bright flashes in Fig. 6. 
The peculiar flash at C (Fig. 4) is an exact counter- 
part of D in Fig. 5. 
This experiment leads me to conclude, therefore, that 
Mr. Clayden’s hypothesis is entirely corroborated, and 
explains very satisfactorily the types of flashes illustrated 
in the above reproductions from photographs. 
In studying Fig. 4 in the light of these results, we can 
form a good idea of the order of appearance of the flashes. 
That marked A was undoubtedly the first to occur (if the 
plate had been immediately developed, it would have 
come out bright); then the flash B made its appearance, 
and, being so intense, illuminated the neighbouring region 
round A that the image of A on the film was affected 
chemically. C was probably next in order of occurrence, 
but, being more distant and therefore fainter, did not 
have any effect on A or B. C, however, was affected by 
subsequent flashes, which were not bright enough to 
illuminate the field to alter the intense bright flash B in 
any way, but which were capable of adding dark borders 
toits sides, The above order of appearance is to a great 
extent corroborated by the apparent distances and in- 
tensities of the flashes. 
There seems very little doubt now that, by varying the 
intensities of the sparks and that of the illuminated 
background, one can produce any combination of bright 
and dark flashes. A glance again at Fig. 6 will show 
that the appearance of a flash depends simply on the 
magnitude and presence or absence of the core. The 
following table sums up the six chief types of flashes 
that probably can be obtained: the reader will notice 
that there is a complete cycle commencing and termin- 
ating with a dark flash. 
1. Dark flash, no core. 
Os »» 95 small bright core. 
{ens flash, broad bright core ; 
: or, 
\ Bright flash, narrow dark borders. 
Bright flash, 720 dark borders. 
small dark core. 
ye & 
This would represent an 
ordinary weak reversal. 
{ Bright flash, broad dark core; | This would represent an 
6. or, ordinary strong reversal. 
| Dark flash, narrow bright borders. 
Dark flash, 0 bright borders ; 
or, 
same as No. I above. 
” ” 
7. 
In the above list photographs have actually been 
obtained of all the types of flashes that came under the 
headings 1-5. I have examined all my zegatives to 
search for the type No. 6, with the result that I have not 
found a representation of this kind of flash. 
It may be remarked that the types 1-3 are produced 
as a direct consequence of the Clayden effect, and should 
therefore only appear on plates which contain more than 
one flash. The other types, which depend simply on the 
intensity of the flash, should be obtained when even only 
one flash appears on a plate.s 
We thus see that actual photographs of lightning bear 
out what we should expect from laboratory experiments, 
and we must therefore answer in the negative the ques- 
tion asked in the first line of this article. 
Dark lightning flashes therefore do not exist in nature, 
but their appearances on photographs are due to some 
chemical action which takes place in the gelatine film. 
In closing this article I wish to draw attention to the 
great interest which is attached to this most fascinating 
subject. Every one who has a camera can help in the 
NO. 1563, VOL. 60] 
elucidation of the several points to be studied, and most 
probably bring new facts to light. The photography of 
lightning flashes during the night is an easy subject, for 
one has simply to turn the camera towards the dark sky, 
and the lightning does all the exposing itself. Unfortu- 
nately it is not every one who is aware of this fact, and I 
know of two instances of amateurs who exposed plates 
during the same storm and at the same place where I 
obtained the above pictures, but they tried te catch the 
Jlashes by using instantaneous shutters. Whether they 
obtained any positive results I do not know, but one 
could make a very fair guess. 
_ Ifany readers of this article would be willing to exchange 
interesting unmounted lightning photographs obtained 
by them for copies of any of the above illustrations from 
the original negatives, the writer would esteem it a 
favour. (Address: 16 Penywern Road, South Kensing- 
ton, S.W.) This request suggests to me that it would be 
important for the furtherance and development of this 
subject, if there were some recognised ‘“ Central-Stelle” 
to which copies of all such photographs could be sent. 
Those studying the subject would not then be so much 
hampered in searching for references to accounts of 
original observations and reproductions, if a fairly com- 
plete collection of copies from original negatives were 
made accessible. WILLIAM J. S. LOCKYER. 
NOTES, 
Pror. A. GRAY, F.R.S., Professor of Physics in the Uni- 
versity College of North Wales, has been appointed to succeed 
Lord Kelvin in the chair of Natural Philosophy in the University 
of Glasgow, and will at once commence his new duties. 
THE Harveian Oration will be delivered at the Royal College 
of Physicians, London, on October 18, by Dr. G. Vivian Poore, 
and the Bradshaw Lecture on November 2, by Dr. A. Foxwell. 
Major RONALD Ross and other members of the Liverpool 
Malaria Expedition have returned to this country very well 
satisfied with their labours. On the advice of the expedition 
the authorities at Sierra Leone decided to use every means to 
exterminate the malaria-spreading mosquito. Major Ross is of 
opinion that the white population is not careful enough, and that 
the houses are badly constructed, and compare unfavourably with 
the residences of white people in India, which are constructed 
on plans that give the inhabitants every chance of health, despite 
the tropical climate. He attaches great importance to this 
question of the construction and situation of the houses. Dr. 
Fielding Ould, a member of the expedition, has remained behind - 
to consult with the medical officers on the coast respecting 
measures to be taken for the extermination of the malarial ~ 
mosquito in the neighbourhood of the principal towns. During 
the investigation one member of the expedition, Mr. Austin, 
suffered from malaria ; he became infected through sleeping one 
night without the protection of mosquito curtains. 
Drs. CALMETTE AND SALEMBENI, who were sent out by the 
Pasteur Institute as a commission to study and combat the 
plague in Oporto, have returned to Paris more than satisfied, it 
is said, with the success attending their efforts with the anti- 
plague serum. Dr. Calmette is of opinion that the Portuguese 
might easily free themselves from plague if they would rigor- 
ously carry out the measures which have been recommended to 
them, and in particular if they would inoculate all the in- 
habitants of suspected quarters. This, however, they appear 
unwilling to do. 
ACCORDING to the Civil and Military Gazette, Lahore, the 
Indian Government has under its consideration a somewhat com- 
prehensive scheme for the establishment of research laboratories 
