May 24, 1883] 



NA TURE 



79 



and made a collection both of its plants and of its animal life. 

 With the exception of my birds and a few of the insects, my 

 collections were destroyed by sea water, so that it is now im- 

 possible for me to give a definite list, but I may note that rats 

 were in such numbers as to have become almost a plague. A 

 goodly herd of introduced fiusas, a cross between the Sumatran 

 (C. eguinus) and Javan (C. Hippelaphits) specie*, were in ex- 

 cellent condition, and were living wild on Direction Island, 

 where also pigs were living in the same state. Among birds, 

 the Gnllus bangkiva (introduced) was inconsiderable numbers ; I 

 saw also the nest of the Phcats hypexaiithus, which comes, not 

 every year, but very often to breed there, but the progeny seems 

 either to die or to return to Java (?). I did not see the snipe, 

 but of the Rallus philippinu s I got several specimens. Egrets, 

 blue and white, abounded and rested on the high trees on some 

 of the islands. Lizards of several species are now found on most 

 of the islands in large numbers. Of insects the number of 

 species is very considerable. Coleoptera were represented by 

 Mtlolonthidii, Cttoniida, Carabid.e, Elater'niic, ChrysonuIicUe, but 

 as I have not my journals of that date by me, I cannot recall other 

 families nor state the number of genera represented. Of Hemip- 

 tera I caught a good many species, mostly of small size. Many 

 species of ants were observed. Neuroptera are represented, un- 

 fortunately, by the termite, introduced some years ago in 

 furniture, it is said, but it occurs now on every islet of the group 

 in myriads. I am told that during the cyclone of a few years 

 ago, the whole surface of the sea was covered wiih the mangled 

 bodies of dragon-flies for miles out to sea, but that sine: then very 

 few have been seen. Of Lepidoptera I caught many species both 

 diurnal and nocturnal, some very handsome, of which I sent a 

 small collection to London in 1879. The Atlas Moth is rather 

 common. Orthoptera were represented by the ubiquitous cock- 

 roach, and a few Acridiidcz. 



Mr. Ross told me that on several occasions the large fruit bat, 

 called the flying fox, has reached the Hands, and once a pair 

 arrived together, but died, from exhaustion apparently, soon 

 after arrival. Under favourable circumstances, as in the case of 

 an unusually strong pair, the-e may yet become inhabitants of 

 the islets. 



There are, I believe, considerable additions to the flora since 

 Mr. Darwin's visit. It is only within recent years that the 

 islands have become so greatly covered with cocoanut plants. 

 Their original vegetation consisted principally of "iron wood" 

 (sideroxylon ?) and other trees, and of low shrubs. These were 

 nearly all burned out by accidental fires, one of which burned 

 for three months. Henry O. Forbes 



Fatunaba, Timor Dilly, January 21 



" Festooned " or " Pocky " Clouds (Mammato-Cumulus) 



Under one of these names letters have appeared at different 

 times in NATURE, notably on October 19, 1871. These were 

 followed by a paper read before the Mete >r. j1 gical Society by 

 Mr. R. H. Scott in February, 1872, in which he collects all the 

 observations which had then been recorded, and the theories 

 which bad been propounded to explain them. 



For several years I have been watching this kind of cloud, 

 and I think that its formation is capable of a very simple ex- 

 planation, partially in agreement with that suggested by Mr. 

 Jevons in the earliest notice of these clouds (Phil. Mag., July, 

 1857). The name is applied to a peculiar festooned appearance 

 sometimes seen below cumulus and stratus clouds. In Orkney 

 Mr. Clouston has found that it is usually followed by a severe 

 gale: but in Lancashire, where the festoons are called "rain- 

 balls." it is only considered a sign of rain. Other o I servers in 

 the tropics have also seen it with thunderstorms, and not neces- 

 sarily with wind. In this country I have observed it both in 

 heavy L:ales and also in an ordinary summer thunderstorm. The 

 method by which I have endeavoured to discover its origin has 

 been to try and trace its life-history ; that is 10 say, to follow its 

 growth from other forms of cloud and to watch the forms into 

 which it develops. 



On one point almost all observers are agreed, that the festoons 

 are frequently seen just before a cloud begins to break up. The 

 first time that I was fairly able to trace the formation of the 

 cloud was one summer evening in London, when towards sunset 

 a flat-based cumulus, like that marked a I in the figure, sud- 

 denly became festo ined at the base and diminished on the top, 

 as marked a 2 in the figure. A few minutes afterwards the 

 whole cloud evaporated. The succeeding night was fine. The 



explanation which immediately suggested itself was that the 

 ascentional current which had formed the flat-based cumulus had 

 suddenly failed, and that the festoons were simply the masses of 

 vapour falling downwards for want of support. 



Another very striking case is marked b in the figure, and was 

 observed before a shower. Here a detached cumulus was ob- 

 served to form first festoons, and then they in turn degenerated 

 into raggy cloud, the whole disappearing very shortly, but was 

 quickly followed by fresh rain-bearing clouds. The impression 

 which the whole conveyed to me was that the festoons were 

 formed by a sudden drop of the cloud, and that the "rag " was 

 produced w hen the drop was less sudden. The appearance of 

 the "rag" is not very well rendered in the diagram, but it is 

 very difficult to delineate clouds by any engraving. 



These are two typical cases of many which I have observed, 

 and always with the same result — that the constant condition 

 necessary for the formation of festoons was the sudden failure of 

 an ascentional current of air. If so, the explanation of its prog- 

 nostic value is very simple. Before many squalls or showers w e are 

 all familiar with the short, abortive gusts which so frequently 

 precede them. Now we have only to assume that the ascen- 

 tional uptake in front of the main body of the shower is as 

 unsteady as the surface wind, and we have at once all the condi- 

 tions of the formation of festoons. Almost all observers agree 

 that they are usually formed at the edges of cloud masses. In 

 the case of rain or thunder they ordinarily appear just before or 

 alter the rain ; but in the case of a gale following some time 

 afterwards, as observed by Mr. Clouston, the festoon must have 

 been formed by some local squall or shower which bore some 



(1.2. 



relation to the disturbed weather which produced the gale. I 

 once saw festoons in the west of Scotland during the hardest 

 gale I have ever seen in this country. They were formed on the 

 outskirts of a north-westerly squall. 



Allied to festooned cumulus we may mention festooned stratus 

 and festooned cirrus. The former is quite common in London 

 during the summer, associated with showers or thunderstorms, 

 while the latter is rare. In both the same idea seems to hold 

 good as for cumulus, that they are formed by the sudden failure 

 of the current, whatever it may be, that forms the stratus or 

 cinus. 



It might appear, at first sight, that a uniform stratus could not 

 fall in lumps ; but however uniform it may seem, viewed from 

 below, there is probably no such thing as a uniform stratum of 

 cloud. Some portions are always denser, or composed of larger 

 drops, and these, falling first, give the "pocky" appearance. 

 In many simple cases, which I have been able to follow, there 

 often seems to be a rough correspondence between bosses on the 

 upper surface and festoons on the lower. In a 2 there is an 

 unsuccessful attempt to depict such a case, which is drawn from 

 nature. 



The name of " festooned cloud " has been objected to as sug- 

 gesting a lengthways arrangement of vapour, like the cloud 

 called "rolled cumulus," with which it has probably nothing in 

 common. Mr. Clement Ley has proposed the name of "tubercled 

 cloud " as more applicable. Prof. Poey, who has also studied 

 this cloud, has proposed the name of " globo-cumulus." 



The general conclusion then, is that festoons are caused by a 

 sudden failure of an ascentional current associated with show ers 

 or squalls, but whether they portend rain or wind depends on 

 the circumstances under which they are observed. 



21, Chapel street, S.W., April 27 Ralph Abercromby 



The Sacred Tree of Kum-bum 



Perhaps the following statement may throw a little light on 

 what was the tree seen by the Abbe Hue : — 



On his voyage home from China the Abbe touched at Ceylon. 

 This must have been in 1852 or 1853, as far as I can recollect. 

 I was invited to meet him at breakfast, at the house of my kind 



