378 



NATURE 



[Aug. 31, 1876 



naturally be asked, What is the cause of this falling-off in 

 the average production ? One reason, no doubt, is that 

 some estates are becoming old, and when an unfavour- 

 able season occurs their cultivation is temporarily un- 

 profitable. But the main cause is most certainly the 

 fungus {Hemileia vastatrix) on the leaves of the plant. 

 This appeared first in 1869, and in 1872 was recognised 

 as a firmly-established cofifee pest. It is generally ad- 

 mitted that the injury is caused through the weakening 

 of the tree by the absorption of the juices of the leaf, for 

 no plant has ever been known to be absolutely killed by 

 the attack or even by a succession of them. The first 

 symptom of the disease is a palish discoloration in spots 

 or patches, easily detected when the leaf is held up to 

 the light. These quickly assume a faint yellow colour, 

 and presently become covered with yellow dust, which 

 soon turns into a rich orange. These are the ripened 

 spores of the fungus aggregated in little clusters, and 

 attached to branching filaments, that have found their 

 way from the air-spaces within the leaf, where they have 

 been feeding on its juices and ruining its vitality. It is 

 estimated that there are sufficient of these spores on a 

 badly diseased leaf to infect 100,000 plants, and therefore 

 it is no wonder that the pest, when once it had come to 

 maturity under the favourable conditions of a coffee 

 estate, should spread in an incredibly short space of time 

 over the whole mountain zone, and that probably within 

 less than two years from its first appearance every coffee- 

 tree in the island had been more or less affected by it. The 

 injury in the first instance appears to be done solely to the 

 leaf, which, at a certain stage of the attack, dies of exhaus- 

 tion, and the tree being an evergreen has to throw out another 

 mass of foliage, which also in its turn becomes affected 

 and dies. Consequently the strength of the plant, which 

 ought to be spent in bearing fruit, is chiefly devoted to 

 putting out new flushes of leaves, whilst a certain per- 

 centage of the crop that is at last ripened is found to 

 have suffered from the general weakness of the tree. For 

 a disease of this kind it is impossible to suggest any 

 remedy, such as sulphuring the leaves. Imagine such 

 an operation as sulphuring more than 250,000,000 trees, 

 and then only obtaining a temporary relief ! Manure 

 gives a tree strength to bear fruit as well as leaves, and 

 therefore is the most approved of all the remedies tried 

 as yet. 



With regard to the origin of the disease, nothing is 

 known, except that it first appeared on a new estate in 

 Madulsima, a district in the south-east of the mountain 

 zone, and bordering on the low country. Mr. Thwaites, 

 the botanist, believes that it has been introduced into the 

 island in imported manure, which is a probable explana- 

 tion of its origin, so far as Ceylon is concerned. Against 

 this supposition, however, is to be set the fact, according 

 to the writer's belief, that Hemileia vastatrix is found in 

 no other country in the world except Southern India, and 

 on no other tree except the coffee-tree. It is, therefore, 

 possible that it may have existed in a modified form, and 

 without attaining any great development on some of the 

 trees in the low country jungle to the eastward, and from 

 them may have been carried by the wind to a neighbour- 

 ing coffee estate. Be this as it may, it is not now likely 

 that its origin will ever be known, unless future research 

 into the nature of fungi throws a light on the subject 

 which it is impossible to anticipate. As to the future of 

 the coffee enterprise in Ceylon, it is useless to predict. 

 Let us hope that the same Providence which has ordained 

 that masses of plants, animals, or men, may not be 

 unnaturally aggregated together without some disease 

 becoming epidemic among them, may also in this case 

 apply the same law for the destruction of the disease 

 itself, by developing among its countless myriads of 

 spores a principle of death, which may cause the plague 

 to disappear as suddenly and mysteriously as it came. 

 Since the above was written, the blossoming season 



has proved so favourable that it is estimated that the crop 

 for the year ending September, 1877, will exceed a million 

 cwts., but whether the plants have suffered so seriously 

 from the attacks of the " leaf disease " as to be unable to 

 bring this crop to maturity time alone can prove. 

 June, 1876 R. Abbay 



OUR ASTRONOMICAL COLUMN 



61 Cygni. — The following formulae for the difference of 

 right ascension and declination of the components of 

 61 Cygni are founded upon a comparison of Bessel's 

 measures with the Konigsberg Heliometer (mean epoch, 

 i835'47) and Baron Dembowski's between 1871 and 1875, 

 on forty-two nights : — 



Aa = + 22-I727 + [874448] [t — 1870) 

 A 5 = — 7-4928 — [9*27780] {t - 1870) 



If the angles of position and distances are calculated 

 from the differences of right ascension and declination 

 thus obtained for the epochs of the older observations, 

 collected by Bessel in his earlier memoir, it will be found 

 that there remains but a very doubtful deviation from 

 rectilinear motion. Bradley's observations, 1 753*8, exhi- 

 bit the largest difference, 3°'9, but having regard to the 

 discordance between the result from Piazzi's observations 

 for i8o6*3 and Bessel's for i8i2"9, both of which can 

 hardly be correct, this difference is not excessive. It 

 appears that the only suspicion of curvature of path must 

 depend upon these early and more uncertain data, as, 

 indeed, was inferred by Mr. Wilson, of Rugby, some time 

 since. 



Tuttle's Comet. — The calculations of Clausen and 

 Tischler have placed the theory of this comet upon a 

 very satisfactory foundation. Discovered in the first in- 

 stance by Mechain, at Paris, on January 9, 1790, it was 

 observed until February i ; a parabolic orbit was com- 

 puted by the discoverer, which subsequently figured in 

 all our catalogues, but there appears not to have been at 

 that time any suspicion of its comparatively short period ; 

 indeed, the short extent of observation might well pre- 

 vent this. On January 4, 1858, the comet was re-detected 

 by Mr. Tuttle, of the U.S. Navy, at the Observatory of 

 Harvard College ; the first elements calculated in this 

 year presented so great a resemblance to Mechain's for 

 the comet of 1790, that the identity of the bodies was 

 immediately inferred, and successive approximations to 

 the period of revolution by Pape and Bruhns, showed 

 that in the sixty-eight years' interval there must have 

 been performed several revolutions, the latter finally con- 

 cluding that the comet had returned to perihelion four 

 times since 1790, though on every occasion it passed un- 

 observed. Clausen (Dorpat Observations, vol. xvi.) cal- 

 culated the perturbations due to the attraction of Jupiter 

 between 1858 and 1790, and thus carrying back the 

 elements deduced from the observations of 1858 to 1790, 

 found but small differences from those obtained from 

 observation in the latter year, which difference was still 

 further reduced after he had included the effect of Saturn's 

 attraction from 1805, January 30, to 1816, August 24, and 

 from 1831, July 17, to 1843, October 22. Tischler's re- 

 sults are published in his " Inaugural Dissertation " — 

 Ueber die Bahn von Tuttl^s Cojiiet, Konigsberg, 1868. 

 In this able investigation of the young astronomer 

 (who unfortunately lost his life before Metz) elements 

 founded upon the observations of 1858 were used for the 

 calculation of the perturbations, on the -method adopted 

 by Bessel for the comet of 1807, from 1858 to 1844, in- 

 cluding the effect of Venus, the Earth, Mars, Jupiter, 

 Saturn, and Uranus, and for all the remainder of the 

 interval the effect of Jupiter and Saturn for every 100 

 days. With these perturbations of the first order, the 

 elements were found for every 6ooth day, and with these 



