334 



NATURE 



[Fed. 2 1, 1878 



different methods given by the Astronomer-Royal for correcting 

 the semi-circular part of the error; one, the square one, for 

 correcting, by two sets of magnets, fore-and-aft and thwart-ship 

 respectively ; the other, the round one, for correcting by a single 

 magnet, or group of bars equivalent to a single magnet, placed 

 under the centre of the compass with its magnetic axis in the 

 proper direction to balance the whole disturbing force on the 

 compass due to that part of the ship's magnetism which is un- 

 changed when she is put on different courses in the same 

 magnetic latitude. The two sets of instructions, in the two 

 printed pamphlets before you, explain sufficiently, for the two 

 binnacles, the arrangements of the magnetic correctors in the two 

 cases, and how to use them in practice. 



The principle in each case is easily understood. In the 

 system employed in the square binnacle the whole constant force, 

 due to the part of the ship's magnetism which remains constant 

 when the ship is put on different courses, is regarded as being 

 replaced by three constant " component" forces in the direction 

 of three lines, at right angles to one another — one fore-and-af^t, 

 one thwart-ship, and the third perpendicular to the deck. The 

 fore-and-aft component is balanced by the fore-and-aft correcting 

 magnets, the thwart-ship component by the thwart-ship magnets, 

 and the component perpendicular to the deck by the heeling cor- 

 rector, which is a bar-magnet, adjustable to the proper height, 

 in a line perpendicular to the deck, through the centre of the 

 compass and of the binnacle. 



In the round binnacle the component perpendicular to the 

 deck is balanced by a heeling corrector, just as in the square 

 one ; but, instead of considering separately two components 

 parallel to the deck, their resultant or the single component 

 parallel to the deck, which, with the component perpendicular 

 to the deck, constitutes the whole force, is balanced by a single 

 magnetic force parallel to the deck. This force is obtained by 

 turning the revolving corrector round the central axis of the bin- 

 nacle, and raising it or lowering it until the proper direction'and 

 proper magnitude of force are produced. 



One novel feature in the last binnacle is the way in which, by 

 aid of the guide-ring graduated to logarithmic cosecants, and 

 the vertical scale graduated to equal proportionate differences of 

 force, the adjustment to correct the compass on one course may 

 be performed without disturbing its accuracy on another coarse 

 on which it has been previously adjusted. The principle of 

 this arrangement is most easily explained by aid of the mathe- 

 matical notation of trigonometry, in connection with the annexed 

 diagram (Fig. 4), in which O represents the compass-card, A, a 

 point of the ship which was in the direction of the correct magnetic 

 north, N, at the time of the first supposed adjustment, ns, the 

 position of the axis of the revolving corrector set to correct the 

 compass on that course, H the ship's head. We have (according 

 to the notation of the instructions) — 

 HOA = II, 

 wOH - C ; 

 therefore, wOA = H -F C. 



Now the correction on the first supposed course, if it did not 

 annul the force due to the magnetism of the ship and cor- 

 rectors, reduced it to a force in the line OA, Hence the com- 

 ponent perpendicular to OA due to the corrector must be kept 

 unchanged in subsequent correction, so as not to disturb the 

 adjustment for that first course. Let F be the magnitude of the 

 force due to the revolving corrector. Its direction being O;/, 

 its component perpendicular to OA is equal to F sin mOA. 

 Hence, if F be increased by raising, or diminished by lowering, 

 the corrector, the angle «0A must be altered so that sin «0A 



shall vary inversely as F, or cosec ;/0A directly as ¥. In other 

 ■p 



words, v^ . must be kept constant, and, therefore, the 



cosec «OA 

 difference between log F and log cosec nOA must be kept con- 

 stant. When the guide-ring is placed according to Rule 2, Sec- 

 tion 4, of the Instructions, the reading upon it is the value of 

 log-cosec (H -f C). The reading on the vertical scale is always 

 proportional to the logarithm of F. Hence Rule 3 secures that 

 the change of magnitude and direction of the correcting force 

 does not vitiate the correction on the course H. 

 {To be continued.) 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 

 Oxford. — An examination for the Burdett-Coutts Scholarship 

 will be held in the University Museum, on Monday, March 11, 



and three following days, at 10 a.m., for the purpose of electing 

 a scholar on that foundation. Candidates are requested to call 

 on the Professor of Geology at 34, Broad Street, with certifi- 

 cates of their standing, and the consent of the head or vice- 

 regent of their College or Hall, on Friday, March 8, between 4 

 and 5 P.M. 



Cambridge. — The exhibition offered by the Clothworkers' 

 Company, to non-collegiate students of the University, for 

 proficiency in physical science, has been awarded to J. G. 

 M'Cubbin, who was educated at the Manchester Grammar 

 School. The exhibition is of the annual value of 50/., and is 

 tenable for three years. The next examination for a similar 

 exhibition open to non-collegiate students who have not resided 

 more than one term, or who have not commenced residence, will 

 be held on July 15 and 17, in connection with the examination 

 conducted by the Oxford and Cambridge Schools Examination 

 Board. Intending candidates can obtain full information on 

 application to the Rev. R. B. Somerset, censor of non- collegiate 

 students, Cambridge. 



Gilchrist Educational Trust.— A course of six Gilchrist 

 Science Lectures for the People, will be delivered in the Bristol 

 Athenceum, by members of the Council and Staff of University 

 College, Bristol, as follows : — February 22, The Action of Heat, 

 by S. P. Thompson, B.Sc. B.A. ; March 5, Heat and the 

 Steam Engine, by J. F. Main, B.A. Camb., D.Sc. Lond ; 

 March 12, The Ocean a Carrier of Heat, by W. L. Carpenter, 

 B.A., B.Sc. ; March 19, Heat within the Safety Lamp, by S. P. 

 Thompson, B.Sc, B.A. ; March 26, the Sun's Heat, by J. F. 

 Main, B.A. Camb., D.Sc. Lond. ; April 2, the Chemistry ot 

 Burning, by W. W. J. Nicol, M.A. The same course is to be 

 given at Bath, Bridgwater, Trowbridge, and Newport (Mon- 

 mouthshire). 



The Birkbeck Institution. — The Lord Mayor has pro- 

 mised to preside at a meeting, to be held at the Mansion House 

 on Wednesday afternoon, the 27th inst., at three o'clock, for the 

 purpose of inaugurating a fund to provide the Birkbeck Institu- 

 tion with a building suitable to its large and important opera- 

 tions, and to enable it to take advantage of the many oppor- 

 tunities for further usefulness which are from time to time 

 presented. As the Institution is doing such an important 

 educational work amongst the young men and women of the 

 metropolis, it is hoped that the friends of education will liberally 

 assist the movement to accomplish so desirable an object. The 

 number of students has been steadily increasing for some years 

 past, and, notwithstanding alterations and extensions of the 

 lauilding, it is impossible any longer to accommodate those 

 attending the Institution. Some indication of the work will be 

 gained from the fact that 3,304 persons joined the Institution 

 during the past term. 



St. Petersburg. — The professors of the High School of 

 Medicine for Ladies at St. Petersburg, among whom are many 

 names well known in science, have addressed a petition to the 

 Minister of Public Instruction, in which they cUiim for ladies 

 who have completed their studies at the high schools, the same 

 degrees as for men. They support their request by pointing out 

 that the five years' theoretical and practical study at the ladies' 

 school are quite as extensive as those pursued by male students, 

 and rather more extensive in the department of female diseases ; 

 that the monthly and yearly examinations have always proved 

 that the ladies possess a very thorough knowledge of their 

 subjects, and finally, that during their service with the army in 

 Roumania and Bulgaria, the ladies have given numerous and 

 sufficient proofs of their high capacity for acting as surgeons. 



Freiburg.— The university is attended at present by 334 

 students, including 41 in the theological faculty, 70 in the 

 philosophicil, 76 in the legal, and 147 in the medicil. It pos- 

 sesses a library of 300,000 volumes, and well-equipped scieniific 

 laboratories and collections, but fails of late years to rank among 

 the influential German universities, partly on account of the 

 rivalry of its neighbours, Tiibingen, Heidelberg, and Strasburg. 



WuRZBURG. — The corps of instructors numbers at present 40 

 ordinary professors, 5 extraordinary professors, and 17 privat 

 docenten. The number of students, 947, shows a decrease of 

 about 50 on the past half year. On January 2 the 296th anni- 

 versary of the foundation of the university was celebrated, and 

 an address delivered by the rector. Prof. Risch, on the national 

 importance of the German universities and their relations to the 

 empire. In the course of the address the Imperial Government 

 was sharply criticised for having, with the exception of the 



