lO 



NA TURE 



[May 2, 1889 



so that there is a dcarga'n, which may be expended in flight 

 until the speed is so much reduced that it is necessary to increase 

 it by another ascent. 



The reason is clear why, when following a steamer against the 

 wind, the birds are compelled to repeat at short intervals the 

 movements by which speed through the air is gained, and why, 

 when the wind is favourable, the intervals are longer. The 

 great 1< ngth of there intervals just mentioned seems to me the 

 difficult point in the theory. It cannot be proved that the speed 

 acquired by the movements described is sufficient for such long 

 flights between the ascents as are sometimes seen, under conditions 

 where there is no suspicion of upward ci rrents near the surface. 

 Our knowledge of the resistance of the air to such complex 

 surfaces as the wings of birds is, I believe, almost nothing ; and 

 even if we knew, without doubt, the true explanation of the 

 manner in which the energy lost by resistance is renewed, we 

 might find it hard to apply it to all cases, unless we had some 

 real knowledge cf the supporting power of the air, and the 

 horizontal resistance at different velocities. 



I have sometimes seen a number of albatrosses sailing in a 

 peculiar manner, the wind being at right angles to the course of 

 the steamer. They ascend against and descend with the wind, 

 turning alternately right and left, so as to describe an undulating 

 line, not far behind the stern. A number of them sometimes 

 do this for hours, whi'e others are sailing in various directions 

 farther off. It is curious that the common sea-gulls of New 

 Zealand {Larus doniinicamis), which have become (o a great 

 extent 'and-birds since the country was colonized, may be 

 sometimes seen iraking their way over flat country in the same 

 manner as the albatrosses just described — that i=, at right angles 

 to the wind, and turning alternately right and left, and nearly 

 touching the ground at each descent. Their success in doing 

 the sailing flight is, however, imperfect, as they seem compelled 

 to flap their wings a few times during the se( ond half of each 

 ascent. Perhaps future generations of gulls may improve. No 

 doubt !^ome muscular exertion is saved by this mode of progres- 

 sion. The foregoing theory of the sailing flight of the albatross 

 shows, I think, the action of a vera causa, which, as far as I 

 know, has not been noticed before. A. C. Baines. 



Christchurch, New Zealand. 



Note on Ragadia crisia. 



Mr. W. L. Distant, in his admirable " Rhopalocera 

 Malayana," calls attention to the recent appearance of Kagadia 

 crisia in the Malay peninsula. As I have had opportunities of 

 studying the habits of the species in what seems to be one of its 

 head-quarters, it may be desirable to record the facts. 



Mr. Distant writes as follows : — "One of the most peculiar 

 facts in relation to this butterfly seems to be its almost recent 

 appearance in the Malay peninsula, or at all events its first 

 capture there by collectors. I did not meet with it myself when 

 collecting at Province Wellesley, nor did I subsequently receive 

 it in numerous collections derived from the peninsula. In 1883, 

 however, the species seems to have been common from Penang 

 to Singapore. I first received two specimens captured on 

 Penang Hill, and sent to me as a new species; others shortly 

 follov\ed from Province Wellesley, with the remark of an ex- 

 perienced collector that the species was quite new to the locality ; 

 and almost simultaneously the Indian mail brought me more 

 examples from Sungti Ujong, Malacca, and Singapore. My 

 friend Mr. Logan also sent me an example with the comment, 

 'a very rare butterfly not known to collectors here.' 



" Capt. Godfrey, who also captured the species at Sungei 

 Ujong, described it as being found in low undergrowth in the 

 forest, where, especially in the early morning, I several times 

 met with it. Its flight is weak and feeble, but it cleverly 

 eludes pursuit by threading its way through tangled brushwood " 

 (" Rhop. Mai.," p. 421). 



Mr. W. B. Pryer, in his joint paper with Mr. Distant ("Rhop. 

 Northern Borneo," Ann. Mag. Nat. Hist., January 1887. 

 p. 49), describes it as "rare, under almost thick forest shade." 

 In ten years' collecting in North Borneo he has only met with a 

 few specimens, not more than a dozen, nearly all of which he 

 saw at Silam, on the coast of the district I write about. 



I find it to be the very commonest butterfly in the dense forest 

 of the centre of Darvel Bay Peninsula, on the east coast of 

 British North Borneo. 



I first saw the insect in the deep forest between Lamag on the 

 River Kinabatangan and Itok Batu on the River Segama, about 



120 miles in'and. It was not common, but I always saw one or 

 two daily. Since then Mr. Pryer has taken it higher up the 

 River Kinabatangan, some 250 miles up stream. The butterfly 

 is still quite rare on the coast, the only specimens having fallen 

 to Mr. Pryer's net. 



Last year I made an exploration through the forest from the 

 River Tinkyo in Darvel Bay to the head-waters of the River 

 Sfgama. Within four miles of the coast, in the alluvial flat of 

 the River Tinl<yo, the species was seen daily, but was far from 

 common. As soon as we touched the mountain country it began 

 to grow common, and from 600 feet to 2500 feet above sea-level 

 it was the commonest butterfly in the deep forest. 



Capt. Godfrey's description of its hal i;s agrees with mine, 

 except in one particular. He found it most plentiful in early 

 morning. I was always in the jungle from soon after dawn to- 

 near dusk, and found it appeared about 9 o'clock in the morning, 

 and was on the wing till about 4 o'clock in the afternoon. 



It has the feeblest (and wickedest) flight of any butterfly 

 known to me. I never saw it rise six feet above the ground, 

 and it flaps slowly along, apparently with eff rt, its wings not 

 stiff but bending with each stroke. It looks a certain capture ; 

 but this, as Capt. Godfrey found, is delusive and elusive. It 

 keeps just above the low bushes from two to three feet high, and; 

 sneaks in among them most exasperatingly. It seems to do this 

 deliberately, and will rather circuit round an opening made by a 

 fallen tree than cress the small opening. It is often seen flying 

 in rain. 



As a rule it is quite solitary, it being rare to see two at once, 

 and it is not at all bold or pugnacious. 



Its wings are so soft that it often crumples in the wet, and it 

 is almost impossible to set it during the rainy season, the wings^ 

 relaxing in a few hours, though it may have been a week on- 

 the setting- board. 



From February to October it was equally common. I then 

 came out of the forest. It probably flies all the year round. 



It is one of the few true forest species, and avoids the sunshine. 



I do not know whether the insect is common elsewhere, and 

 can offer no suggestion as to why it should be spreading from 

 this part, though it is undoubtedly creeping coastwards. The 

 eastern part of North Borneo is untouched primaeval forest, the 

 cnly clearings being on the coast and river-l anks, and these are 

 small. The country where Kagadia abounds is quite uninhabited, 

 and it is difficult to see how the food-plant (unknown) could 

 have been taken thence to the Straits Settlements. Then too, 

 in Borneo at any rate, it would avoid clearings. 



Leaving this question for future observers to solve, we now 

 know that in one part of the interior of North Borneo Kagadia- 

 crisia is very common, and it is extending its area. 



Sydney B. J. Skertchi.y. 



Spherical Eggs. 



Prof. Aldis will find references to the history of this ancient 

 question in an article by Mr. W. Walton in the Quarterly 

 Journal of Mathematics, vol. ix. p. 79, where it appears as 

 Leslie Ellis's problem of the thirsty crow, "A thirsty crow 

 flew to a pitcher and found there was water in it, but so near 

 the bottom he could not reach it. Seeing, however, plenty of 

 small, equal spherical pebbles near the place, he cast them one 

 by one into the pitcher, and thus by degrees raised the water up 

 to the very brim and satisfied his thirst. Prove that the volume 

 of water must have been to that of the pitcher in a ratio not less 

 than 3 fjz - ■"■ : 3 sj^.''^ References are supplied in the article by 

 the Rev. Dr. Luard to Pliny's "Natural History," book x. 

 chapter 43, "De Corvorum Intelligenlia" ; Plutarch, " De 

 Solertia Animalium ; and .-Elian, " De Natuva Animalium." 

 Consult also Tail's " Properties oi^ Matter." 



Thus in an aggregation of closely- packed equal spherules the 

 unoccupied space is i - j7r^/2 of the whole volume. 



We may verify this experimentally by comparing the weight 

 of a given volume of small lead shot with the weight of an 

 equal volume of lead ; theoretically the densities should be as ir, 

 to 3 ^2. 



On a larger scale, the question may be studied in the piles of 

 spherical shot form.erly to be seen in our forts and arsenals. 

 Whether we begin piling the shot in horizontal layers, in tri- 

 angular order, or in square order, the internal molecular arrange- 

 ment of the spheres is the same ; but the square order in the 

 horizontal layers is preferred, as it is then possible to build the 

 pile on a rectangular ba=-e, fini^hing off at the top with a ridge 



