204 



NATURE 



[October 21, 19 15 



objectives described in these tables are not given 

 the forms determined by the astronomical tele- 

 scope conditions — freedom from colour, central 

 spherical aberration, and coma — but one of these 

 is deliberately sacrificed to enable the crown and 

 flint components to be cemented together. This 

 leads to the consideration of six forms of objec- 

 tive, three of which have the crown lens before 

 the flint and three with these lenses in the reverse 

 order, two forms of each set of three being free 

 from colour and from central spherical aberration, 

 and one free from colour and from coma. Each 

 of these forms is described in a separate group of 

 tables. 



With most of the glass combinations one of 

 the forms with the crown lens placed before the 

 flint has the two surfaces of the crown lens of 

 nearly equal curvature, and a set of tables is 

 included devoted to lenses in which these curva- 

 tures are exactly equal. Such lenses offer the 

 very considerable advantage when rapid output 

 and low cost is of importance, of requiring only 

 two sets of tools for their production, one set 

 corresponding to the equal curvatures of the 

 crown lens and the surface of the flint lens which 

 will be cemented to a face of the crown com- 

 ponent, the other set being, of course, for the 

 second surface of the flint lens. 



To each group of tables giving the construc- 

 tional details of its own particular type of 

 lens is added a table showing the amount 

 of the aberration — coma or spherical aberration, 

 as the case may be — which has unavoidably 

 been retained in consequence of the re- 

 straint imposed by the condition that the two 

 components are to be cemented to one another, 

 A glance at these tables shows which form of 

 objective and what combinations of glasses are 

 the most suitable to employ in various cir- 

 cumstances. The physical interpretation to be 

 placed on these quantities is explained in a note 

 which prefaces the tables. For convenience 

 in reference all the tables relating to one form 

 of objective are placed on a single opening of the 

 pamphlet. 



The fundamental tables relate to lenses in 

 which the thicknesses are negligible. A second 

 set of tables is added, showing the alterations in 

 focal length produced by standard thicknesses, 

 which are taken to be i/4oth of the focal length 

 for the crown component and i/8oth of the focal 

 length for the flint lens, and also the corrections 

 to the curvatures which are necessary to give the 

 thick lenses the same focal length as those of 

 negligible thickness. For convenience in making 

 such corrections the principal set of tables give 

 the curvatures of each lens surface in addition to 

 their radii of curvature. The foregoing par- 

 ticulars suffice to show that the pamphlet should 

 not only be of immediate use to those for whom 

 it has more especially been prepared, but should 

 prove of permanent value to all who are engaged 

 in the construction of small objectives. It may 

 be obtained from the publishers, Messrs. Harrison 

 and Sons, 45 St. Martin's Lane, London, W.C. ; 

 price 2s. 6d., plus postage. 

 NO. 2399, VOL. 96] 



The laboratory authorities state that it is hoped 

 later to supplement this publication by a further 

 paper dealing with the corrections which may be 

 necessary for object glasses of somewhat larger 

 size. They may also undertake further optical 

 calculations needed to perfect instruments re- 

 quired by the naval and military authorities if it 

 seems to them desirable. 



T. Smith. 



R. W. Cheshire. 



JEAN -HENRI FAB RE. 



IT is more than half a century since Darwin 

 quoted Fabre in his " Origin of Species " and 

 called him "that inimitable observer." Yet he 

 has been with us and working till the other day — 

 a resolute veteran, in spite of his extraordinarily 

 hard and strenuous life, from which he wrung 

 out the joys of discovery and devotion. In this 

 sense he lived a successful life, and he had other 

 rewards — the appreciative esteem of expert en- 

 tomologists ; the admiration of those who have 

 enjoyed his intimate descriptions of the life and 

 work of insects and his singularly vivid style ; 

 the encouragement of good friends, such as John 

 Stuart Mill and Mistral ; but one cannot escape 

 the regret that, through imperfections in con- 

 temporary social organisation, his genius, which 

 was marked by a unique blend of observing power 

 and sympathetic insight, was through a large part 

 of his life unduly distracted and inhibited by the 

 cares of keeping up the supply of daily bread. 

 Perhaps on his own side he carried the spirit of 

 independence to an extreme. In any case there 

 is a pathetic ring in his own words, a short time 

 ago, about his life, that it "had not been exempt 

 from many cares, nor very fruitful in incidents 

 or great vicissitudes, since it had been passed 

 very largely, especially during the last thirty 

 years, in the most absolute retirement and the 

 completest silence." The ten volumes of the 

 "Souvenirs Entomologiques," many of the best 

 chapters of which have been translated into 

 English, remain as Fabre's lasting monument. 

 They show us an observer of insects, second only 

 to R(^aumur, who was able, in a way all his own, 

 "instinct pursuing instinct," as has been well 

 said, to get at the insect's point of view. 



After a somewhat disappointing early struggle 

 as a professor at Ajaccio and Avignon, Fabre re- 

 coiled from conventionalities and settled down on 

 a little desert corner near Orange, in the lower 

 Rhone, and subsequently at Serignan, and gave 

 himself up to entomology. His studies were occa- 

 sionally anatomical and physiological, and he 

 watched many life-histories ; but he was pre- 

 eminently the student of animal behaviour. 

 His work is marked by strong vitalistic 

 convictions, organism to him transcending 

 all mechanism ; by a belief in instinct as 

 a big underivable fact, quite different from 

 intelligence; and by a strong prejudice against 

 Darwinism, even against evolutionism. "The 

 facts that I observe," he said, "are of such a kind 

 that they force me to dissent from Darwin's 



