NATURE 



{Sept. 26, 1889 



year by year, and also the greater tendency towards 

 accurate results, call for a book containing all the various 

 rules and tables relating to those parts of mathematical 

 and mechanical science whose application most 

 frequently occurs in the useful arts, and especially in 

 engineering and practical mechanics. In this volume of 

 moderate bulk, such a work has been provided. The use 

 of algebraical symbols has been avoided as much as 

 possible, excepting in those cases in which the rules 

 cannot be clearly expressed without them. 



The book is divided into ten parts. The first deals 

 with arithmetic and mensuration, including tables of 

 cubes, squares, logarithms, a summary of the rules in 

 trigonometry, with tables of arcs, sines, &c., concluding 

 with the measurement of areas of surfaces, volumes of 

 solids, and lengths of curves, &c. Part 2 treats of the 

 measures of different nations, with tables and rules 

 relating not only to measures of angles, time, length, sur- 

 face, &c., but to those of speed, heaviness, pressure, work 

 power, &c. Engineering geodesy, distributive forces and 

 mechanical centres, balance and stability of structures, and 

 strength of materials are included in the next four parts. 

 Part 7 relates to machines in general, and gives rules for 

 the comparison of the motions of different parts of a 

 machine, and for the designing of teeth of wheels, speed 

 cones, &c., with rules relating to work at uniform and 

 variable speed. Parts 8 and 9 treat of hydraulics and 

 heat, together with the steam-engine. The former in- 

 cludes rules for flow of water, pi'ime movers, propulsion 

 of vessels, &c. ; the latter consists of tables of elasticity, 

 volume, and specific heat of gases, factors of evaporation, 

 with rules relating to furnaces, boilers, expenditure of 

 heat in cylinders, efficiency of strain, &c. 



Part 10, written by Andrew Jamieson, has been revised 

 and considerably extended, and consists of electrical 

 rules, tables, and formute. The information has been 

 brought up to date as much as possible, and many points 

 of diflSculty, such as directions of currents, magnetic 

 force and motion, are made clear by means of illustra- 

 tions. Electrical engineering symbolsand units of measure- 

 ment, heat, and light are first given. These are followed 

 by various forms of Wheatstone bridges, apparatus for 

 testing electric light cables, the wire-testing batteries on 

 the General Post Office system, tables of resistance, 

 general data of the different submarine cables and 

 batteries. 



In the appendix there is a useful diagram of the 

 mechanical properties of steam, showing the absolute 

 pressure in pounds per square inch, and volumes in cubic 

 feet per pound of dry saturated steam, and the mean 

 absolute pressure, in decimal parts of absolute pressure 

 of admission. A complete index adds greatly to the 

 value of the work ; and we may say that the more one 

 looks through the pages of the book the more one is 

 struck by the large amount of useful information collected 

 together in these 456 pages. 



Colour. Bv C. T, Whitmell. (Cardiff: Wm. Lewis, 

 i88«.) ' 



This book is designed for the general reader, and is, 

 on the whole, well suited to this class of person. The 

 principal drawback it possesses is unquestionably the 

 want of a good index, while the division into short 

 numbered sections of in many cases a few lines only is very 

 inconvenient, and produces a sensation of discontinuity 

 of subject. Some parts are excellently done, notably the 

 illustrations given of irregular reflection by turbid media, 

 the description of colour produced by absorption, and the 

 part dealing with colour-blindness. In connection with 

 this last subject much extension of our knowledge would 

 no doubt result from systematic observation of the pro- 

 gressive development of colour-blindness in cases of 

 locomotor ataxy. 



It is to be regretted that the author did not supply 



coloured diagrams to at least some of the sections, or 

 failing this it would be more suggestive in the diagrams of 

 light transmitted through different specimens of coloured 

 glass to shade the part representing the absorbed and to 

 leave unshaded that representing the transmitted light. 

 Some preliminary description of the optical apparatus 

 employed would be also serviceable, e.g. in section 10 the 

 reader is told the properties of a spectrum produced by a 

 diffraction grating, no reference being made until much 

 later, and then a very incomplete one, as to the principle 

 involved in the formation of the spectrum. 



The book is fairly up to date, containing as it does 

 reference to Langley's bolometric observations and to 

 Konig's researches on the theory of colour vision. In- 

 teresting cases are given of errors due to ignorance of 

 scientific principles ; and in view of the frequency of 

 their occurrence— perhaps more noticeably from neglect 

 of the effects of refraction than of the principles of 

 colour — it is regrettable that manuals such as Church's, 

 Rood's, or this, are not more generally read by painters. 



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 of NATURE,. 

 No notice is taken of anony?nous communications. ] 



Sailing Flight of Large Birds over Land. 



It gave me great pleasure to see, by Lord Rayleigh's letter 

 in Nature of May 9 (p. 34), that the remarks made by me 

 some months ago on this subject were not made in vain. 



Ever since 1863, the sailing flight of large birds (which is 

 here very common) has been a subject of observation to me, and 

 odd notes have been sent home to the English Mechanic and 

 to the Aeronautical Society (see Sixteenth Report, 1881, pp. 

 10-17). 



Mr. A. Baines, in Nature of May 2 (p. 9), well describes 

 the sustained sailing of the albatross, indicating what I take to 

 be the vera causa, i.e. the rising, kite-like, when it sweeps round' 

 to meet the wind, the energy of motion being gained by de- 

 scending with it along an incline. But this problem, as seen 

 among the sea-birds, seems to be complicated by the possibility 

 of lifting action due to the waves ; and, in Mr. Baines's letter, 

 by different velocities of the air near the sea surface and at ele- 

 vations of 20 feet or so. Out here, these two features are not 

 only eliminated, but we see the bird doing more work. 



The sea-birds merely sustain for hours a given weight, say 

 twenty pounds, without flapping the w ings, whereas the land- 

 birds lift this twenty pounds, in two or three hours, to a height 

 of I or 2 miles vertically, as well. 



The adjutants {Leptotilus argala and nudifrons), the cyrus, 

 pelican, vultures of several kinds, and storks, habitually rise 

 here during fine weather, if there is a wind. At first they rise 

 by flapping the wings vigorously, and, when 200 or 300 feet up, 

 gradually begin to sail in huge right- or left-hand spirals, rising; 

 30 or 40 feet at each lap. When seen thus, the wings are rigidly 

 extended, and tail spread, the primary wing feathers distinctly 

 separated, and a loud musical tone is heard as the bird sweeps 

 round and round overhead. If low down, they can be closely 

 studied through a binocular, but if at a great height, I generally 

 use a telescope, 3" -5 O.G., and terrestrial eye-piece, power 40. 

 With this latter I can follow them, either in a group or singly, 

 until each is a mere speck, and the elevation can be fairly cal. 

 culated, when the spread of wing is often 8 or 9 feet x i^. 



Our prevailing north-east wind, and also our south-west mon- 

 soon, are particularly steady air-drifts of, say, 5 or 6 to 10 miles 

 per hour, and I should doubt very much, if, after 500 feet up, 

 there is any variation in the speed at diff'erent heights. The 

 lifting due to occasional waves should also here be out of the 

 question, and under these conditions I would ask Lord Rayleigh 

 where we could possibly obtain the " energy of position " if it 

 is not from the kite-like action ? In my former note, to which 

 he refers, I think a small diagram illustrated the slow drift to> 

 leeward as the bird rose by sailing in spirals. 



