November 1, 1888.] 



KNOW^LEDGE ♦ 



Darwin, so that the older view that corals built upon these 

 cones was reasonable and probable. Tlie cone, if rising 

 above the surface, would soon be reduced by the action of 

 the waves to a suitable level, or if too low, might be raised 

 by organic deposits. Upon this the true reef-forming corals 

 would commence to build. The outer surface being always 

 in the most favourable position with regard to food supply, 

 the edge would tend to reach the surlVice first. 



Mr. Murray lays great stress upon the power of the sea- 

 water (always containing carbonic acid, especially at great 

 depths) in dissolving the coral which has ceased to grow, 

 and to this cause he attributes the deepening of the central 

 lagoon in an atoll, and the lagoon channel in a barrier reef. 

 " Thus growing .seawards on its outer face, and dissolving 

 away in the lagoon, the whole expands after the manner of 

 a fairy-ring, and the ribbon or reef of land can never in 

 consequence increase beyond half or three-quarters of a mile 

 in width " (" Journal of the Eoyal Institution," 1888). The 

 greater e.xtent of coast line in a small atoll, as compared 

 with its contained lagoon, is probably the reason why the 

 latter has been frequently filled up, fragments torn from the 

 outside being carried over the rim by waves, and piled in 

 the interior. 



The power of sea-water to dissolve coral structures has 

 been investigated, and proved by laboratory experiments, 

 but it is still a question whether the action upon small 

 detached pieces can be compared with that which would 

 take place with the massive coral limestone of the 

 reefs. There is also evidently a difficulty in understanding, 

 as Mr. Darwin justly observes in a letter dated September 

 1880, and published in "Nature," November 17, 1887, how 

 " there should be rapid dissolution of carbonate of lime at 

 gi-eat depths [where few calcareous remains are found] and 

 near the surface [in the deepening of lagoons] but not at 

 inteimediate depths where he [Mr. IMurray] places hLs 

 mountain peaks." Captain Wharton t has given several 

 inhtances of entirely submerged atolls in the China seas in 

 which the height of the rim above the lagoon is quite as 

 great as in atolls which have reached the surfixce. 



Murray's views with regard to the volcanic foundation of 

 coral reefs are strongly supported by Dr. Cuppy's observa- 

 tions.'* He observes : " These upraised reef masses in the 

 majority of the islands rest on a partially consolidated 

 de[iosit, which possesses the characters of the volcanic muds 

 that were found during the Challenger expedition to be at 

 present forming around volcanic islands." Dr. Guppy infers 

 that the depo.sit envelops anciently submerged volcanic 

 peaks. 



Mr. Bourne, in his interesting account of the atoll of 

 Diego Garcia (which has a channel laading into the lagoon) 

 in the Indian Ocean, previou.sly quoted, shows that the 

 reef is teing worn away by tidal scour on its Iwjoon side, 

 while the exterior is protected by the growing coral. 

 Within the lagoon the corals only exist in patches, their 

 gi'owth being checked by the deposit of sediment. The 

 Diego Garcia observations strongly support the view that 

 coral growth proceeds most rapidly in a Jiorizontal rather 

 than in a vertical direction, as required by Darwin's theory. 



Perhaps in the present state of our knowledge it will be 

 wisest, as Dr. Guppy has suggested,t to regard as pos.sible 

 all the various agencies which have been suggested as 

 ])roducing the various forms of reef. Outside thero are the 

 directing influence of currents, the increased food supply, 

 and the action of the lireakers. Witiiin the lagoon are the 

 repressive influences of sediment, the boring of the numerous 

 organisms that find a home on every reef, the solvent influ- 



* " The Solomon Islands." 

 t " Nature," vol. x.xxvii. 



ence of carbonic acid, and the tidal scour. In some places 

 also it is possible that subsidence may have played its part. 



The bird's-eye view of Caroline Wand has teen copied 

 from an excellent plate given in Professor Holden's Eeport 

 of the 1883 Eclipse Expedition. 



[We have been disappointed at the last moment in the 

 receipt of two other woodcuts which were expected to 

 illustrate this article. — Ed.1 



HENRY DRAPER MEMORIAL. 



11. HENRY DRAPER, of New Vork, who 



was the first to photograph a nebula, suc- 

 ceeded in 1872 in obtaining several photo- 

 graphs of the spectra of stars. His father 

 — nearly thirty years previously — had 

 obtained the first photograph of a human 

 being, as well as the first photograph of the 

 dark lines in the solar spectrum, both of these earlier photo- 

 graphs lieing taken on .silver plates. At the time of Dr. 

 Henry Draper's death in 1882, he was proposing to devote 

 himself for several years to the photography of stellar 

 spectra, making a catalogue of the spectra of all stars which 

 could be photographed with the means at his disposal. His 

 widow has raised a most suitable memorial to his memory, 

 and that of his father, by providing funds for the establish- 

 ment of a new department of Harvard College Observatory, 

 where, under the superintendence of Professor E. C. Picker- 

 ing — and with the aid of the 15-inch refractor and the 

 28 -inch reflector used by Dr. Henry Draper, and other 

 instruments which have since been devised by Professor 

 Pickering — a spectroscopic catalogue of the heavens is being 

 made, and photographs of the spectra of the brighter stars 

 are being taken on a scale commensurate with the photo- 

 graphs of the solar spectrum taken only a few years ago. 



Such large-scale photographs of the spectra of stars open 

 out great possibilities in the near future of astronomy, for 

 they will enable us to measure the velocities of stars in the 

 line of sight (to or from the observer) with a much less 

 percentage of error than the distances of the stars cjin be 

 determined from measures of parallax. The apparent proper 

 motion of stars (which can be determined very accurately 

 from measures of their positions taken at intervals of many 

 years) gives a guide to their velocities in directions at right 

 angles to the hue of sight, and with the motion in the line 

 of sight accurately known, we shall be able to form a much 

 juster notion of stellar distances and stellar motions than 

 has hitherto been attained to. 



THE EFFECTS OF COMPETITIVE 

 EXAMINATIONS. 



llOFESSOll DE MORGAN, who was certainly a 

 most successful teacher if we estimate success 

 by the number of distinguished mathema- 

 ticians who were educated under him, delivered 

 an introductory lecture, some forty years ago, 

 on the evil ettects of competitive examination, 

 in which he stated that he considered such 

 examinations to be among the crudities of an im])erfect 

 system, and to be as inoflectual in gaining the end either of 

 makimj the best scholar or showiiuj the best scholar, as its 

 moral tendency is bad. The lecture was printed at the 



