376 



NATURE 



L.">».i IhMBER 8, 1923 



than hydrogen. The origin of this radiation ^3727, 

 therefore, seems to be one of the most interesting 

 and difficult problems which the astrophysicist has to 

 deal with at the present time. 



We will now pass on from the Orion Nebula, which 

 may be taken as a good example of the irregular 

 gaseous nebula; connected with ' B " type stars, to 

 the planetaries. Here we have to deal with involved 

 central stars which are of the " O " type, of a con- 

 siderably higher temperature. In the spectra of these 

 nebulae the doublet X(5oo7, 4959) is still usually 

 the strongest radiation, and hydrogen is invariably 

 present. On the other hand, X3727 is often compara- 

 tively faint or absent altogether, although X3869 is 

 still one of the strongest radiations in the spectrum. 

 Ionised helium at X4686 is also very conspicuous, but 

 ddes not extend far from the nucleus, showing that 

 ionisation only takes place in the neighbourhood of 

 the star itself. Another bright radiation at X3426, 

 found in the spectrum of Nova Cygni III, also makes 

 its appearance, but its extension from the nucleus is 

 small. 



A very remarkable feature in the high dispersion 

 spectra obtained with the three-prism spectrograph 

 of the Lick 36-in. refractor was the character of the 

 lines under magnification. When the slit of the 

 spectrograph was placed across the major diameter 

 of the planetary nebula disc, the resulting lines in 

 the doublet X(5oo7, 4959) were not parallel-sided, but 

 spread out in the centre, each end being slightly 

 curved in opposite directions. If we are to interpret 

 this phenomenon on the Doppler principle in the 

 usual way, this means that the gases are both receding 

 from us and advancing towards us in the line of 

 sight, coupled with a slight rotation of the gaseous 



spheroid as a whole. The only fe.i is 



that the gaseous shells forming - H 



expanding, and we are at once le<i to a (.omp..- -n 

 with novae such as Nova Aquilx III, which now iias 

 developed an expanding gaseous disc. 



The later spectroscopic stages of novae are con 

 parable in every detail with the planetary nebnli 

 the galactic distribution of both is similar, an<l li.t 

 evidence is now overwhelming that the planet.irj- 

 had their origin in novae, anci the gaseous shells « 

 the planetaries are the remains of past outbursts. ! 

 may be asked why the planetary' nebulae are con 

 paratively few in number, but it is evident that 

 the central star fell to a lower temperature th;' 

 " B " type, the radiation would be insuflficient ■ 

 to keep the gases in a state of equilibrium or \ 

 illuminate them, and the asp>ect of a planetary nebu! 

 would disappear. The same remarks apply to oi 

 like the (jrion Nebula connected with " B " 

 stars. Here the radiation energy is not so intense 

 the " O " stars, and we do not get an equal degT< 

 of ionisation : the strength of the radiation X3727 ; 

 also evidence of different physical conditions, but tl 



Orion and other irregular gaseous nebula; have ' 



appearance of being swept away from the in\ 

 stars, and they all probably indicate a former ouii-^i -^ 

 of several stars culminating in an " O " type of 

 spectrum and a high radiation pressure. 



The old idea that the gaseous nebulae were the 

 primitive forms of matter from which stars were 

 evolved must, it seems, be given up for the exact! 

 contrary hypothesis that they had their origin ; 

 stellar outbursts, where matter passed from com pi ( 

 to simpler forms by atomic* disintegration under th 

 stress of extreme temperature development. 



Plants in Relation to the Health of Man.^ 



/^INCHONA. the plant which yields quinine, 

 ^ known under the name of "Jesuits' Powder" 

 since 1655, was introduced into India about the years 

 1858 to 1862. Seedlings and seeds were brought to 

 Great Britain from the Andes of Bolivia during those 

 years, principally by Sir Clements Markham and Mr. 

 Richard Spruce, and the plants, which were raised at 

 the Royal Botanic Gardens, Kew, were taken to India 

 and Ceylon. The cultivation in India was mainly 

 established in the Nilgiri Hills and in Sikkim. The 

 three species of Cinchona which are particularly 

 valuable as sources of quinine are C. Calisaya, C. 

 Ledgeriana, and C. succirubra. 



The Dutch had also been experimenting with 

 Cinchona and established the plant in Java about the 

 same time as the English were introducing it to 

 India. So successful have the plantations been in 

 India, thanks to the labours of Dr. Thomas Anderson, 

 Sir George King, Messrs. Wood and Gammie and Sir 

 David Prain, that in every post office in India it is 

 now possible to procure doses of from seven to ten 

 grains of pure quinine for a pice, which is about equal 

 to a farthing. In this way, more than eight thousand 

 pounds avoirdupois of quinine are distributed yearly, 

 and in addition to this a large supply is furnished to 

 hospitals, etc. Efforts are now being made to extend 

 the cultivation of quinine in Malaya and Burma. 

 Substitutes for Cinchona as a source of quinine were 

 used in the Cameroons by the Germans during the War. 



Other interesting plants are Efwatakala grass, 

 Melinis minutiflora, which is reported to be obnoxious 

 to the tsetse fly ; citronella grass, the source of 

 lemon grass oil, which is repellent to mosquitoes ; and 

 Ocimum viride, the Basil plant, which at one time 



• From a Chadwick public lecture delivered by^Dr. A. W. Hill, F.R.S., 

 at the Chelsea Physic Garden, on June 13. 



was thought to be repellent to mosquitoes, but now is 

 known to be of no value for the purpose. 



In connexion with the preservation of the health 

 of man in temperate climates, the plants yielding 

 india-rubber are of first importance. The princip^ 

 source of india - rubber is Hevea brasiliensis (Para 

 rubber). This again is a native of South America. 

 Seeds and young plants have been distributed to the 

 various tropical colonies of the British Empire since 

 the year 1873, when it was brought over from South 

 America, mainly owing to the successful efforts of Sir 

 Henry Wickham. Other sources of rubber are the 

 Ceara rubber, Ficus elastica, Funtumia, and the 

 tropical African Landolphias. The rubber now used 

 commercially is mainly derived from plantations in 

 the East, to which region it was introduced through 

 the Royal Botanic Gardens, Kew. 



Another source of protection against damp and 

 cold is furnished by the various plants which yield 

 tannin, the preservative of leather. The principal 

 sources of this are oak galls and bark, mangrove 

 bark, Myrobalans, Quebracho, and Acacia decurrens. 

 Extensive plantations of the latter plant, which is a 

 native of Austialia, have been made in South Africa 

 and are a source of considerable wealth to Natal. 



Cinnamomum Camphora, which is a native of 

 Formosa, is the source of camphor, valuable as a 

 drug and also a preservative of clothing against moth. 

 Trade in camphor is a monopoly of the Japanese, but 

 seeds have been freely introduced to British colonies, 

 largely through the agency of Kew. It is now found 

 there are two forms of camphor, but only one of these 

 yields the solid camphor which is of value. 



Erythroxylon Coca is the source of cocaine, the 

 alkaloid which has so many useful as well as harmful 

 effects. 



NO. 2810, VOL. I 12] 



