Feb. 21, 1878] 



NATURE 



331 



in the western suburbs of London, and perhaps also in other 

 parts. Two remedies are recommended for warding off the 

 insects ; one by scattering amongst the plants some pulverised 

 gas-lime, and the other by watering with the liquid from pig- 

 sties. The clouded yellow butterfly {C alias edtisa) was, it seems, 

 "the great appearance of the year," and was first seen near 

 Dumfries early in June, and across the south of England it was 

 generally observable from June till October. The frequent death 

 of the larvae when feeding on various clovers and trefoils is men- 

 tioned as a point of interest relatively to its permanent settlement, 

 as also the great difference in the quantity of the sexes noticed 

 at various stations which may be followed ,by coincident variety 

 of appearance next year. The report is published by Mr. T. P. 

 Newman, Botolph Lane, Eastcheap, from whom we believe 

 copies may be obtained. Every information on the subject will 

 also be supplied on application to the Rev. T, A. Preston, The 

 Green, Marlborough, Wilts, E. A. Fitch, Esq., Maldon, Essex, 

 or Miss E. A. Ormerod, Dunster Lodge, Spring Grove, Isle- 

 worth. 



The St. Petersburg University has addressed a note to the 

 Ministry of Public Instruction requesting that the necessary steps 

 be taken for the preservation of any valuable manuscripts which 

 rnay be found in the Turkish towns occupied by Russian troops. 

 Valuable manuscripts were preserved in this way from destruction 

 in the War of 1829, and important manuscripts have already 

 been discovered in the mosques of Tirnova. 



A SMALL Japanese " blue" book comes to us in the shape of 

 a report by the department of Public Hygiene on some of the 

 mineral waters of the country and the uses to which they may be 

 put. Japan seems to contain a great variety of such waters. 



At the meeting of the Musical Association on February 4 a 

 paper was read by Mr. D. J. Blaikley, * ' respecting a Point in 

 the Theory of Brass Instruments." The necessary difference in 

 form between such instruments and conical tubes was pointed 

 out, and a new experimental method for determining the posi- 

 tions of the nodal points in tubes, especially applicable to such 

 as are of varying section, was shown. As an instance may be 

 given a conical tube open at both ends and of the pitch C 512 

 vib. The node is nearer the small than the large end of the 

 tube, and by sinking one end in water and holding a fork of the 

 pitch of the tube over the other, the exact position of the node is 

 shown by the level of the water when the tube is giving its maxi- 

 mum resonance. 



The additions to the Zoological Society's Gardens during the 

 past week include two Macaque Monkeys {Macacus cynomolgus) 

 from India, presented by Lieut-Col. Fielden ; a Grivet Monkey 

 {Cercopithecus griseo-viridis) from North- east] Africa, presented by 

 Mr, E. H. Lockley ; a Garden's Night Heron {Nycticorax 

 gar dent) from South America, presented by Mr. Henry Bottrell ; 

 three Chimpanzees {Troglodytes niger) from West Africa, 

 deposited ; a Black-faced Spider Monkey {Ateles ater) from East 

 Peru, a Collared Peccary {Dicotyles tajafu) from South America, 

 a Globose Curassow [Crax globicera) from Central America, a 

 Black-footed Penguin (Sphertiscus demersus) from West Africa, 

 a Hey's Partridge {Caccabis heyi) from Arabia, purchased. 



ON COMPASS ADJUSTMENT IN IRON SHIPS 1 



I. — New Form of Marine Azimuth and Steering Compass with 

 Adjuncts for the complete Application of the Astronomer- Roy aV s 

 Principles of Correction for Iron Ships. 



'T^HIRTY-EIGHT years ago the Astronomer-Royal showed 

 •^ how the errors of the compass, depending on the influence 

 experienced from the iron of the ship, may be perfectly corrected 



> Report of paper read to the Royal United Service Institution, February 

 4, by Sir Wm. Thomson, LL.D., F.R.S., P.R.S.E., Professor of Natural 

 Philosophy in the University of Glasgow, and Fellow of St. Peter's College, 

 Cambridge. Revised by the Author. IThe Council of the U.S.I, have kindly 

 permitted us to publish Sir W. Thomson's paperin advance, and have gr-.nted 

 us the use of the illustrations. — Ed. J 



by magnets and soft iron placed in the neighbourhood of the bin- 

 nacle. Partial applications of his method came into immediate use 

 in merchant steamers, and within the last ten years have become 

 universal not only in the merchant service, but in the navies of 

 this and other countries. The compass and the binnacles before 

 you are designed to thoroughly carry out in practical navigation 

 the Astronomer-Royal's principles. The general drawback to 

 the complete and accurate realisation of plans for carrying out 

 these principles heretofore, has been the great size of the needles 

 in the ordinary compass which renders one important part of the 

 correction, the correction of the quadrantal error for all latitudes 

 by masses of soft iron placed on the two sides of the binnacle, 

 practically unattainable ; and which limits, and sometimes par- 

 tially vitiates, the other chief part of the correction, or that 

 which is performed by means of magnets placed in the neigh- 

 bourhood of the compass. Five years ago my attention was 

 forced to this subject through my having been called upon by 

 the Royal Society to write a biographical sketch of the late 

 Archibald Smith, with an account of his scientific work on the 

 mariner's compass and ships'. magnetism, and I therefore com- 

 menced to make trial compasses with much smaller needles 

 than any previously in use ; but it was only after three years of 

 very varied trials, in the laboratory and workshop, and at sea, 

 that I succeeded in producing a mariner's compass with the 

 qualities necessary for thoroughly satisfactory working in all 

 weathers and all seas, and in every class of ship, and (""yet 

 with small enough needles for the perfect application of 

 the Astronomer-Royal's method of correction for iron ships. 

 One result at which I arrived, partly by lengthened trials at 

 sea in my own yacht, and partly by dynamical theory analogous 

 to that of Froude with reference to the rolling of ships, was that 

 steadiness of the compass at sea was to be obtained not by 

 heaviness of needles or of compass-card, or of added weights, but 

 by longness of vibrational period * of the compass, however this 

 longness is obtained. Thus, if the addition of weight to the 

 compass-card improves it in respect to steadiness at sea, it is not 

 because of the additional friction on the bearing-point that this 

 improvement is obtained ; on the contrary, duhiess of the 

 bearing-point, or too much weight upon it, renders the compass 

 less steady at sea, and, at the same time, less decided in showing 

 changes of the ship's head, than it would be were the point 

 perfectly fine and frictionless, supposing for the moment this to 

 be possible. It is by increasing the vibrational period that the 

 addition of weight gives steadiness to the compass ; while, on the 

 other hand, the increase of friction on the bearing-point is both 

 injurious in respect to steadiness, and detrimental in blunting it 

 or breaking it down, and boring into the cap, and so producing 

 sluggishness, after a short time of use, at sea. If weight were 

 to be added to produce steadiness, the place to add it would be 

 at the very circumference of the card. My conclusion was that 

 no weight is in any case to be added, beyond that which is 

 necessary for supporting the card ; and that, with small enough 

 needles to admit of the complete application of the Astronomer- 

 Royal's principles of correction, the length of period required for 

 steadiness at sea is to be obtained, without sacrificing freedom 

 from frictional error, by giving a large diameter to the compass- 

 card, and by throwing to its outer edge as nearly as possible the 

 whole mass of rigid material which it must have to support it. 



In the compass before you (Fig. i), these qualities are given by 

 supporting the outer edge of a card on a thin rim of aluminium, 

 and its inner parts on thirty-two silk threads or fine copper wires 

 stretched from the rim to a small central boss of aluminium, 

 thirty-two spokes, as it were, of the wheel. The card itself is of 

 thin strong paper, and all the central parts of it are cut away, 

 leaving only enough of it to show conveniently the points and 

 degree-divisions of the compass. The central boss consists of a 

 thin disc of aluminium, with a hole in its centre, which rests on 

 the projecting lip of a small aluminium inverted cup mounted 

 with a sapphire cap, which rests on a fixed iridium point 

 (Figs. 2 and 3). 



Eight small needles from 3^ inches to 2 inches long, made of 

 thin steel wire, and weighing in all fifty-four grains, are fixed 

 like the steps of a rope ladder on two parallel silk thread?, 

 and slung from the aluminium rim by four silk threads or fine 

 copper wires through eyes in the four ends of the outer pair of 

 needles. 



The weight of the central boss, aluminium cup, and sapphire 



» The x'ibrational period, or the period (as it may be called for brevity)of a 

 compass, is the time it lakes to perform a complete vibration, to and fro, 

 when dellecled horizontally lliruiigh any angle not e.xcceding 30" or 40", anil 

 left to itself to vibrate freely. 



