July II, 1889] 



NATURE 



245 



astigmatism, and chromatic aberration, and their reme- 

 dies, are all fully considered. A useful bibliography is 

 also appended to each chapter. 



Les Levers Photographiqiies, et la Photographie en 

 Voyage. By Dr.' Gustave Le Bon. Part I. (Paris : 

 Gauthier-Villars et Fils, 1889.) 



This work treats of methods of obtaining by means of 

 photography elevations and plans of monuments, build- 

 ings, &:c., the intention being to render unnecessary the 

 laborious tasks and long calculations which up to the 

 present time have been unavoidable. 



The modifications a camera has to undergo before 

 operations are begun consist of the addition, first, of an 

 india-rubber support fitted between the camera and the 

 tripod, and, secondly, of a graduated ground glass in the 

 place of a plain one. The india-rubber support is to enable 

 the camera always to assume a horizontal position in what- 

 ever position the tripod may be ; the ground glass thus 

 being parallel to the face of the building which is about 

 to be photographed. There is also an arrangement by 

 which the camera can be rotated. By means of the 

 ground glass the dimensions of objects can be easily 

 measured, and horizontal and vertical angles can be 

 read off. 



The first few chapters relate to methods of graduating 

 this glass, and its employment in the measurement of 

 angular distances, also the mode of determining the focal 

 lengths of the lenses employed, and the measurement of 

 the sizes of objects after they have been photographed. 

 Chapter v. treats of the general principles of photographic 

 perspective, followed by the applications of those prin- 

 ciples to the solutions of various problems, such as, "To 

 determine the height of an inaccessible tower by a single 

 photograph ; " " To obtain without any measurement on 

 the object itself its various dimensions,'' &c. Lastly, 

 Chapter vi. deals with photographic triangulation and 

 methods of measuring large base lines. 



The Itdernational Annual of Anfhotiys Photographic 

 Bulletin. Edited by W. J. Harrison, F.G.S., and 

 A. H. Elliot, Ph.D., F.C.S. (London: Illiffe and 

 Son, 1889.) 



This is the second issue of an interesting and use- 

 ful work. The number of articles has been con- 

 siderably increased, and there is also an increase in 

 the number of tables at the end, which will be of ser- 

 vice both to professional and to amateur photographers. 

 Various methods of printing are displayed in the illus- 

 trations. Two pretty views are given, one of which is 

 taken with Dallmeyer's long-focus rapid landscape lens, 

 and the other with his wide-angle landscape lens, 

 showing well the effect of these different focus lenses. 

 No pains seem to have been spared to make this issue 

 surpass the first one, and the editors are to be congratulated 

 on the results of their labours. 



Industrial Education. By Sir Philip Magnus. (London : 

 Kegan Paul, Trench, and Co.) 



The articles and addresses brought together in this 

 volume form a valuable contribution to the study of one 

 of the most important and interesting questions of the 

 present day. Sir Philip Magnus has not attempted to 

 exhaust his subject, or to deal with it systematically. He 

 merely presents it from various points of view, offering 

 suggestions as to the urgent need for a proper technical 

 training, and as to the methods which may be most fitly 

 used for the attainment of the ends in view. Every page 

 bears witness not only to the writer's general knowledge 

 and ability, but to his practical familiarity with all the 

 aspects of the problems he discusses. One of the best 

 papers in the book is that in which he gives an account 



of the school system of Bavaria, whose educational ar- 

 rangements are not so well understood in this country as 

 those of Prussia, No one who reads this paper, and 

 takes into account all that has been done for education in 

 the other States of Germany, will find much difficulty in 

 explaining the fact that in industry and trade the Ger- 

 mans have become our most formidable competitors. 

 Another excellent paper is on mercantile training, arid 

 there is also a good paper on technical instruction in 

 elementary schools. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents . Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part ^^Nature. 

 No notice is taken of anonymous communications. ] 



An Index to Science. 



I AM glad to see that Mr. Taylor Kay has again brought for- 

 ward the question of a subject index to scientific periodicals. I 

 say again, because the proposal to make such an index was 

 suggested by me in a short letter in Nature, vol. xviii. p. 251, 

 and more fully at the first meeting of the Library Association 

 at Oxford, in October 1878 (Transactions of Library Asso- 

 ciation, 1878, p. 85). Dr. Garnett also read a paper before 

 the same Association on this subject in 1879, which was fully 

 printed in Nature, vol. xx. p. 554. In my original letter 

 I suggested making the index from the papers themselves, and 

 not Irom the Royal Society's Catalogue ; my reason for this 

 was the difficulty that must be experienced in indexing many 

 papers, should the indexer have nothing but the title in front of 

 him. Reference' to the paper is absolutely necessary in many 

 instances, especially when the title does not fully set forth its 

 contents. Dr. Garnett, however, pointed out that much labour 

 might be saved if the Royal Society would give two copies of 

 its Catalogue of Scientific Papers, which might be cut up to 

 form the copy of the subject-index. There can be no doubt 

 that Dr. Garnett is right, because, by his plan, however many 

 papers it might be necessary to refer to, the amount of labour 

 as regards manuscript would be very materially diminished. 

 The greatest difficulty of all is the money. Mr. Taylor Kay 

 takes comfort in a Treasury Minute of November 1864, and 

 hopes, from that, that help might be obtained from the Govern- 

 ment. I am afraid, however, it will damp his ardour to be told 

 that the Government have refused to bear the cost of printing 

 the Catalogue for the decade 1874-83, although the matter is 

 all ready for the press. It seems to me that, as suggested in my 

 original paper, the co-operation of the learned Societies is the 

 only way in which the necessary funds can be obtained. 



I gather from Mr. Taylor Kay's paper that he rather suggests 

 a "classified" list of papers. If that be so, I would like to 

 protest against such an undertaking, feeling sure that it will, 

 like all its predecessors, be doomed to failure. What is wanted 

 is an index pure and simple, in which information can be turned 

 up without consideration as to what "class" or "classes" the 

 indexer has thought fit to enter the subject under. Anyone 

 who has used the admirable catalogue of Dr. Billings will at 

 once admit its superiority to any "classified" arrangement, 

 whether it be that of Comte or of any other philosopher. 



The question of this index has been hanging fire too long, 

 and I should be delighted if Mr. Taylor Kay's paper were the 

 means of some active steps being taken to start the work. 

 Poole's Index is a standing answer to those who say it cannot 

 be done. All that we want are willing hands and a long purse : 

 if the scientific Societies or an enterprising publisher will find 

 the latter, I cannot believe the former will be wanting. 



James Blake Bailey. 



Royal College of Surgeons, July 5. 



A Cordial Recognition. 



I HAVE just witnessed a curious case of bird instinct which 

 seems worth recordmg. A gardener living at Zukaleria, three 

 miles from here, caught in his garden a young but fully fledged 

 sparrow, which he brought to the house of a friend with whom 



