
Fepruary 17, 1923] 
NATURE 
223 

The phenomenon was observed for about thirty 
minutes, when it was blotted out by heavy, dark 
clouds from the south-west. Within a short time 
the sky was darkly overcast and rain began to fall, 
lightly at first, accompanied by slight fog ; later rain 
fell very heavily, the raingauge giving a total of 1:97 
inches for the afternoon. 
The mirage was seen by practically all the residents 
at the station. 
The meteorological conditions do not point to 
anything extraordinary. The synoptic chart for 
7 A.M. shows an anticyclone centred westward of 
the mouth of the English Channel, with a very slight 
ridge of high pressure extending over Ireland and 
up the West Coast of Scotland. The temperatures 
at 7 A.M. were 48° at Wick and Stornoway, 51° at 
Castlebay, and 55° at Aberdeen. There was therefore 
a fairly sharp discontinuity of temperature along a 
line just south of Cape Wrath. The wind at 7 A.M. 
at Cape Wrath was from west by north. By I P.M. 
a secondary depression had advanced from the 
Atlantic, and was centred about 50 miles north of 
Stornoway, giving a south-westerly trend of isobars 
over the coast line from Cape Wrath to Dunnet 
Head. The temperature at Stornoway was now 52°, 
but only 47° at Wick, where the wind was still 
light. 
othe mirage was seen at 10.30 A.M., at the time 
when the wind was backing in front of the depression. 
The Deerness anemograph shows a slight backing of 
the wind from west by north at 10.30, and a further 
slight backing to west by south about 11 a.m. The 
wind blew steadily from west by south until 3.30 P.M., 
when it shifted to north in the rear of the 
secondary. 
It will be noted that the phenomenon occurred at 
a time when the warmer current in front of the 
secondary depression had not completely displaced: 
the colder air from the immediate vicinity of the 
coast line. There would remain a cold pocket of 
air under the cliffs, and other masses of cold air 
would probably be trapped by the hills near the 
coast. 
The only suggestion which I can offer as a basis 
of explanation for the phenomenon is that there was 
a sharp surface of discontinuity—approximately 
vertical—between the warm air over the sea and the 
cold air under the cliffs, and that some distance 
inland there was another nearly vertical surface of 
discontinuity between the cold air near the coast and 
warm air which had penetrated inland through a 
gap in the hills south of Cape Wrath. 
eflection of light at two such surfaces of dis- 
continuity would account for the phenomenon, the 
effect being that produced by two mirrors, one in 
front, and one behind, the observer. There should 
be a small amount of reflection at any sharp surface 
of discontinuity, perhaps sufficient to account for 
the phenomenon being visible through a telescope. 
The extremely small limit of the region from which 
the phenomenon was visible would place the inland 
discontinuity near to the observer. The effective 
surface of the mirror may have been quite small. 
Mr. Anderson records that there was a slight fog 
when the rain came. The fog would be produced 
by the mixing of the warm humid current with the 
colder air which had previously remained over the 
coast. 
The phenomenon has been called a mirage, but 
the mirage as ordinarily understood is either an effect 
of refraction in air stratified horizontally, or, in the 
case of inverted mirage, is an effect of reflection at 
a horizontal surfacé at which there is a rapid change 
NO. 2781, VOL. III] _ 

of density. But the admitted theory of formation 
of inverted images confirms the claim that there 
should be reflection at a surface of discontinuity of 
density. The phenomenon described above might 
perhaps be named a “ vertical-reflection mirage,”’ 
to distinguish it from the ordinary mirage due to 
refraction or reflection in air stratified horizontally. 
No other records of similar phenomena can be 
traced, probably on account of the fact that such 
mirages are never likely to be visible to the naked 
eye. The telescope is useful in such cases only in so 
far as it limits the amount of light reaching the 
observer’s eye. A plain tube without lenses would 
probably have shown the mirage more clearly than a 
telescope. 
Mr. Anderson has been keeping a watch for others, 
but so far without success. This particular observa- 
tion has been perhaps due in part to a series of happy 
accidents, in that the observer happened to be in 
the best position to note the effect, at the time when 
a wandering sheep roused his curiosity. Much credit 
is due to him for the trouble he has taken to draw 
the map and sketch, and to write a very detailed 
account of what he saw. 
D. Brunt. 
Meteorological Office, Air Ministry, 
January 26. 

The Sugar-Cane Mealy-Bug. 
I HAVE just received a very interesting paper on the 
sugar-cane mealy-bug (Pseudococcus sacchari Ckll.) 
from Mr. W. J. Hall, of the Ministry of Agriculture, 
Egypt. He describes the insect as being so injurious 
that ‘‘the whole future of the industry hangs in 
the balance.’’ When I was recently in Madeira I 
examined the sugar-canes wherever I went, and found 
only a sparing and local infestation by P. sacchari. 
I had no microscope with me, but the determination 
was confirmed by Mr. E. E. Green. The insects may 
be found on the canes near the cliffs below the new 
road, a short distance west of Funchal. It is certainly 
worth while to determine why the pest is so serious 
in Egypt, and scarcely noticeable in Madeira. It 
may be that there is more damage in Madeira than I 
thought, but probably some efficient parasite will be 
found there. By collecting a quantity of the white 
material and placing it in a box, the parasites might 
.be bred. That there is a parasite we know for certain, 
as my first sending from Funchal to Mr. Green could 
not be positively determined, consisting only of a 
mass of waxy secretion with fragments of the 
coccid, along with larve and pupe of a parasitic 
Dipteron. 
It is worth while to record at this time the occur- 
rence of a really dangerous pest in Madeira, the 
Aleurothrixus howardi (Quaintance), on citrus in Dr. 
Grabham’s garden in Funchal. It was determined 
for me by Dr. A. C. Baker of the U.S. Department of 
Agriculture. The infestation, while local, was very 
heavy, and if the insect spreads it may become a 
serious menace to the cultivation of oranges and 
related fruits. 
Another potential pest found in Madeira is the 
rose-weevil Pantomorus fulleri (Horn). A_ single 
specimen was given to me by Mr. A. C. de Noronha, 
who found it in the vicinity of Funchal. It was 
identified by Dr. G. A. K. Marshall. As no other 
specimens have been found, it has perhaps not 
succeeded in getting established. 
T. D. A. COCKERELL. 
University of Colorado, 
January 2. 
