July 1, 1898.] 



KNOWLEDGE. 



126 



mathematical accuracy. Baily, accordingly, in his 

 edition of Ulugh Beg's Catalogue (Mi'inoirs of tlw 

 Hoijal A.^trotutnticdl Socii'ty, Vol. xiii.) identities without 

 hesitation the cscliatns tou jiotnmoii with 9. This had 

 been done long before by Halley in his Cutalni/us 

 Stfllaniiii AiisfraliiiDi, and the wonder is how, with the 

 great weight of Halley on the other side, the idea should 

 ever have gained ground that a, Eridani is the (•.icImUis lnu 

 potaiiioti. 



We have also from the pen of Sufi (1104 a.d.) a very 

 clear description of the Last in the Kiver. He has been 

 describing the three closely-adjacent fourth magnitude 

 stars Lacaille 1108, 12-14, 1248 (often called respectively 

 /), / and // Eridani ■'), and goes on to say : — 



" The ::?4th star (in Eridanus) precedes these three, and 

 the distance between it and that one of the three which is 

 nearest to it " (i.e., Lacaille 1198 or li Eridani) " is about 

 4 cubits " (/.<'., about 9° 20' of arc ; Sufi's cubit = 2° 20' : 

 '■(>/(• page 92 of Schjellerup"s edition). " It is of the first 

 magnitude. This is the star marked on the southern 

 astrolabe and called Achernar. Preceding this bright 

 star there are two others, one to the south, the other 

 to the north. Ptolemy has not mentioned them. One 

 of these stars is of the fourth magnitude, the other of 

 the fifth. Following it, and at a distance of 2 cubits 

 from it " ( = 4° 40' of arc), " there is a star of the fourth 

 magnitude." 



It needs only a glance at the map to see what star is 

 meant by Sufi. The bright star that precedes h Eridani 

 (Lacaille 1198), and is distant from it about 9' 20' of 

 arc, can only be 5 Eridani. (The actual distance between 

 the two stars is 9° 11'.) The two stars preceding 5 — one 

 of the fourth magnitude lying southwards, and one of 

 the fifth magnitude lying northwards — are t Eridani and 

 V Fornacis respectively. The fourth magnitude star that 

 follows it is f Eridani (Lacaille 1060). 



That the star intended by Sufi cannot possibly be a 

 Eridani is evident from the fact that that star is distant 

 from /( Eridani, not four cubits but 27^° of arc, or more 

 than eleven cubits. It is much to be regretted that Prof. 

 Schjellerup, the able and industrious translator of Sufi, has 

 allowed this to escape his notice, and helped in the preface 

 and notes to his work to propagate the delusion that a. 

 Eridani is Ptolemy's Last in the River. It is, perhaps, 

 too late now to restore to 9 its ancient style and title of 

 Achernar, but a at least should be made to yield up its 

 usurped honours. 



What rank did 9 Eridani hold in the heavens in ancient 

 and mediajval times '? Sufi, in placing it among his first 

 magnitude stars, places it m an exceedingly select circle, 

 for he has only thirteen stars of undoubted first-class 

 rank, the other eleven, besides /3 Leonis and the Last in 

 the River, being Capella, Vega, Arcturus, Aldebaran, 

 Regulus, Procyon, Eigel, Sirius, Fomalhaut, Canopus 

 and a Centauri. He estimates Betelgeuse and Spica as 

 1 — 2, Altair and ji Centauri as 2 — 1, and Pollux and 

 Antares as only 2. 



One fact about ^ Eridani we shall probably never learn, 

 unless a certain contingency occurs. The fact to be 

 ascertained is, which of the two components of 9 has 

 faded '? The contingency is that the star may brighten up 

 again. In a few centuries it will be high enough above 

 the horizon to be visible in Britain. Will it then shine 

 upon our land in its pristine glory as Ptolemy saw it gleam 

 over the sands of the desert, and Sufi watched its image 

 dancing on the waters of the Tigris '? 



* Not k, g and i, as stated by Prof. Schjellerup in his edition 

 of Sufi. 



GALLS AND THEIR OCCUPANTS.-L 



By K. A. BuTLEK. 



IN the recent articles on " Caterpillars' Dwellings," we 

 have seen how certain insects use parts of plants 

 for the double purpose of board and lodging, twisting 

 the leaves into variously-shaped coverings, the in- 

 terior of which is then eaten away. In all such 

 cases the portion of the plant operated upon is a normal- 

 vegetable product, and our interest and admiration are 

 called forth solely by the ingenuity and architectural skill 

 with which the insect, always in its larval form, adapts 

 for its own purposes the materials it finds ready to hand. 

 We propose now to consider some far more remarkable 

 instances of association between insects and plants, 

 in which a suitable action on the part of the parent 

 insect results in the production of an nbnori/iaJ vegetable 

 growth, destined to provide its oflspring with both shelter 

 and food. These abnormal growths are of the most varied 

 forms, some of them appearing as mere swellings or 

 unsightly excrescences, others as highly ornamental addi- 

 tions, resembling leaves or fruit ; but whatever their form 

 and appearance, they are all included under the one name 

 " galls." By a gall, then, we are to understand any kind 

 of abnormal vegetable growth which results from the 

 puncture of a plant by an adult insect, and the insertion 

 of an egg in the puncture, the vegetable growth thus 

 formed nourishing and protecting the larva produced from 

 the egg, and sheltering the pupa resulting from this, till 

 the time of its emergence as a perfect insect. Some of 

 these galls are among the most familiar of " common 

 objects of the country," such e.ij. as oak-apples, oak- 

 spangles, and robins' cushions, while the gall-nuts of 

 commerce, used in the manufacture of ink, owe their origin 

 to a similar cause. In these cases, the presence of the 

 insect inhabitant, shut up as it is in the centre of the gall, 

 is very naturally often quite unsuspected, and the oak- 

 apple, for example, looks superficially as much like the 

 genuine fruit of the oak tree as the acorn itself. The 

 nature of the gall produced is no doubt to some extent 

 dependent upon the plant upon which it is found, but it 

 is much more largely dependent upon the species of insect 

 that produces it, for the same kind of insect always pro- 

 duces the same sort of gall, while different insects will 

 produce galls of totally different character, not only on 

 the same tree, but even side by side upon it, where the 

 vegetable conditions must be precisely similar. 



The insects which are resjionsible for the formation of 

 these monstrosities are usually sombre-coloured, fly-like, 

 insignificant creatures, which are commonly known as 

 gall-flies. They belong chiefly to two orders : the 

 Hymenoptera, or order of bees, wasps, and ants, and the 

 Diptera, or two-winged flies. The former order, however, 

 contains all the best known species. Some few galls are 

 produced by insects of other orders, but the consideration 

 of these we will defer for the present. Our first concern 

 will be with the hymenopterous gall-producers. These 

 will fall mainly into two families — the Cynipidm, or gall- 

 flies proper, and the Ti-nthredinidct, or saw-flies. All the 

 species of the former family are in some way or other 

 connected with galls, while in the latter group the habit 

 pertains to only a few. 



It will give greater definiteness to our thoughts if we 

 select one particular species of Cijnijjidtc as typical of the 

 group, and none could be found better suited for the pur- 

 pose than that which produces the so-called marble or 

 Devonshire galls of the oak tree, Cijnips KoUari. The 

 galls are no doubt familiar objects to anyone who has 



