March 3, 1921] 



NATURE 



II 



of which is 29-31 mm. This is the race cimensis of 

 Wollaston. About the landing-place, on the east side, is 

 another race, smaller than usual (maximum diameter 

 22-25 iTirn-)» i^ot dark, but well and conspicuously 

 banded, and with the spire greatly depressed. It may 

 be called race evoluta; it has possibly become dis- 

 tinctly segregated since Wollaston 's time, since it 

 combines the characters of the other forms, and is 

 the sort of thing which might doubtless be obtained 

 from them by careful breeding under artificial condi- 

 tions. At the same time these races cimensis and 

 evoluta exist to-day as pure types, very distinct and 

 easily recognised, occupying different stations on the 

 Ilheo de Cima. 



In some ways the Ilheo de No'-deste, the most 

 remote of the islets about Porto Santo, is even more 

 interesting. It is a mere rock in the ocean, about 

 500 metres long and 300 metres high, somewhat less 

 than 3 km. from the main island. With the aid of 

 our boat's crew of strong Portuguese sailors, my wife 

 and I were able to land and climb about the exces- 

 sively rocky surface. The vegetation is scanty, but 

 includes the beautiful stock, Matthiola inaderensis, 

 Lowe, and the orange-flowered Lotus. Ants and 

 millipedes seemed to be entirely absent. On this 

 lonely rock, and nowhere else, lives the beautiful snail 

 Cryptaxis forensis, Wollaston, with dark, keeled shell 

 and pink lip and apex. Here, and not elsewhere, 

 is found (in great abundance) the small, button-like 

 Dlscula polymorpha race gomesiana, Paiva. But here 

 also is the invading Helix pisana and the native Plebe- 

 cida punctulata, Sowerby, which abounds on the 

 main island. 



The curious little Geomitra pauperctda, Lowe, 

 abounds under rocks in dry places at Porto Santo 

 and on the adjacent islets. It is unique in the group 

 for its wide distribution, being found also in Madeira 

 and all three Desertas, and in the Azores and Canaries. 

 It sticks very tightly to the rocks or to any other 

 convenient object. I once saw a beetle (Helops) walk- 

 ing along with one of these snails on Its back. It is 

 probable that at different tim.es these snails have 

 attached themselves to the feet of birds, and thus 

 got carried across the sea. 



The soundings taken many years ago by H.M.S. 

 Styx (Capt. Vidal) show that Porto Santo rests on 

 an elevated bank, indicating a former island perhaps 

 six or seven times as large. The margins of this 

 bank appear to be clifT-like, almost vertical, the 

 depths suddenly increasing from, e.g., 45 to 200 

 fathoms. This might be taken to indicate the cliffs 

 of the former island, perhaps dating from the 

 Mesozolc. The oldest deposits on the island contain- 

 ing fossils are Miocene, and are marine. At Calheta 

 Point one may see this Miocene material, with large 

 shells and corals, mixed with dark volcanic rock, 

 which seems to have been thrust up from beneath. 

 The suggestion is obvious that the island dates only 

 from the Miocene, but, apart from the Styx soundings, 

 it seems improbable that the remarkable snail fauna 

 has wholly evolved from some immigrant or immi- 

 grants since that time. The sandv fossil beds con- 

 taining land shells must be considered Pleistocene. 

 Wollaston calls these shells subfossil, but they are 

 quite comparable with Pleistocene fossils elsewhere, 

 and show about as much difference from the living 

 fauna as might be expected. At the base of this 

 series, in the Campo do Baixo, is a dense stratum of 

 marine Pleistocene, which has been studied and will, 

 I hope, be fully described by my friend Senhor A. C. 

 de Noronha, a verv keen and able naturalist who was 

 born in the island. 



The insect fauna of Porto Santo is scanty, but the 

 collections obtained will doubtless prove to be of ex- 



NO. 2679, VOL. 107] 



ceptional interest when studied. Three species of 

 butterflies are common, Colias edtisa, Vanessa cardui, 

 and V. callirhoe, the last breeding abundantly on the 

 nettle Urtica membranacea, Poir. Wollaston con- 

 sidered that specimens of the Porto Santo V. cal- 

 lirhoe were smaller than those of Madeira, but I 

 could not see any difference. We found only two 

 species of bees, both Andrena. No fossorial 

 wasps could be found, though the sandy country 

 seemed exactly suited to them. The numerous 

 spiders appear to have no Pompilidae to attack 

 them. At the back of the town rises the tall 

 Pico do Castello, and on its summit may be seen a 

 building in which the inhabitants used to take refuge 

 from the Moorish pirates. A cannon remains on the 

 side of the mountain, half-buried in the earth. To-day 

 the lowlands of Porto Santo are overrun, like those 

 of Madeira, by the obnoxious little ant Iridomyrrnex 

 hurmilis, which has exterminated the once-abundant 

 house-ant, Pheidole megacephala. But on the top of 

 the Pico do Castello we found the Pheidole still hold- 

 ing out, with numerous strong nests. 



The flora is scanty, and was not specially studied 

 by us. We were interested to find the orchid Gennaria 

 diphylla, Lk., on the Pico do Castello and Pico 

 d'Anna Ferreira. The Pico do Castello has been 

 extensively planted with trees in recent years, and I 

 thought the orchid might have been introduced with 

 soil, but this seems unlikely in the case of the Pico 

 d'Anna Ferreira, which remains in its original 

 condition. 



The people of Porto Santo are a hardy and indus- 

 trious race who win a scanty living from the sea and 

 soil. We found them exceedingly friendly and cheer- 

 ful, and left them with strong feelings of regard. 

 We were specially indebted to our guide, Senhor Juan 

 do Pico, who knew every path and bywav. 



T. D. A. COCKERELL. 



Hotel Bella Vista, Funchal, Madeira, 

 February 3. 



The Energy of Cyclones. 



In the recent discussion in Nature on the energy 

 of cyclones no mention has been made of tropical 

 cyclones, although these are the most remarkable 

 phenomena of their kind. 



It is impossible to apply to these cyclones the 

 theories which ascribe the energy of the rotating wind 

 system to the re-adjustment of equilibrium of warm 

 and cold masses of air within that system, since in 

 the cyclones of the tropical zone temperature and 

 humidity are symmetricallv distributed. In these 

 cyclones warm and cold sectors do not exist. The 

 Indian meteorologists Henry Blanford, Sir John Eliot. 

 Fr. Chambers, and W. T. Willson have published 

 papers on the cyclones of the Bay of Bengal and the 

 Arabian Sea, giving a full explanation of their origin 

 and development. These very important works no 

 longer receive the attention thev deserve. They also 

 throw much light upon the source of energy in these 

 cyclones. I endeavoured to make a rough calculation 

 of the energy contained within one of these whirls, 

 taking into account the preceding pressure distribu- 

 tion over the hurricane region, and the results were 

 in good agreement with the observed wind forces. I 

 should therefore like to direct attention to this work. 



The calculation was based upon observations of the 

 Backergange cyclone. It is given in my " Lehrbuch 

 der Meteorologie " (1901 edition, p. 579, footnote), as 

 well as in a paper, *' Remarks on the Origin of 

 (Tropical) Cyclones " (Meteorologische Zeitschrift, 

 1877, August, p. 311). My calculation has no ap- 



