94 



NA TURE 



[May 24, 1883 



It is now proposed to consider the effects of a change of 



magnetic latitude on the component parts of the deviation. 



Semicircular Deviation 



On semicircular deviation from fore and aft forces, time has 

 but little effect, and the greater part of it is due to permanent 

 magnetism in hard iron which may be reduced to zero for all 

 latitudes by a permanent magnet. 



A second hut small part of this semicircular deviation proceeds 

 from sub-permanent magnetism in hard iron. It is subject to 

 alterations slowly by time, from concussion, and from the ship 

 remaining in a constant position with respect to the magr.etic 

 meridian for several days, and is more intensely affected by a 

 combination of the two latter causes. 



Deviations from sub-permanent magneti -in which have tem- 

 porarily altered in value as described, return slowly to their 

 original value on removal of the inducing cause. 



The principal cause of change in the semicircular deviation on 

 change of magnetic latitude, in corrected compasses arises from 

 vertical induction in soft iron, which changes directly as the 

 tangent of the dip. 



In standard compasses judiciously placed with regard to sur- 

 rounding iron this element of change is sm.ill and similar in 

 value for similar classes of ships. 



With very few exceptions, nearly the whole of the semicircular 

 deviation from transverse forces is due to permanent magnetism 

 in hard iron subject to the same laws as that proceeding from 

 fore and aft forces. 



In the exceptional cases alluded to there is a small part due to 

 vertical induction in soft iron, changing directly as the tangent of 

 the dip. 



Quadtantal Deviation 



This deviation is caused by induction in horizontal soft iron 

 symmetrically placed, and it does not change with a change of 

 magnetic latitude. Time alone appears to cau-e a gradual 

 change in its value during the first two or three years after the 

 ship is launched, when it becomes nearly permanent. 



The diminution of the mean directive force of the needle which 

 is common to all modern vessels of war, improves slowly at first 

 by lapse of time, and finally assumes a permanent value. 



Relative Proportions of Hard and Soft Iron 

 It has been found that the relative proportions of the hard and 

 soft iron affecting the standard compasses of twenty-five vessels 

 examined differ considerably, even in ships of similar con- 

 struction. 



This difference may be accounted for by the compasses not 

 being placed in the same relative position in the ships, considered 

 as magnets of various forms and containing numerous iron bodies 

 introduced during equipment. 



General Conclusions 



The following general conclusions have special reference to 

 the standard compass positions in the six classes of vessels pre- 

 viously mentioned. 



1. A large proportion of the semicircular deviation is due to 

 permanent magnetism in hard iron. 



2. A large proportion of the semicircular deviation may be 

 reduced to zero, or corrected, for all magnetic latitudes, by fixing 

 a hard steel bar magnet or magnets in the compass pillar, in 

 opposition to, and of equal force to, the forces producing that 

 deviation. 



3. A very small proportion of the semicircular deviation is 

 due to sub- permanent magnetism, which diminishes slowly by 

 lapse of time. 



4. The sub-permanent magnetism produces deviation in the 

 same direction as the permanent magnetism in hard iron, except 

 when temporarily disturbed (i) by the ship's remaining in a 

 constant p isition with respect to the magnetic meridian for 

 several days, (2) by concussion, or (3) by both combined, when 

 the disturbance is intensified. 



5. To a-certain the full value of changes in the sub-permanent 

 magnetism, observations should be taken immediately on the 

 removal of the inducing cause. 



6. In the usual place of the standard compass the deviation 

 caused by transient vertical induction in soft iron is small, and of 

 the same value (nearly) for ships of similar construction. 



7. The preceding conclusions point to the conditions which 

 should govern the selection of a suitable position for the standard 

 ■compass with regard to surrounding iron in the ship. 



Anthropological Institute, April 24. — "Prof. W. H. Flower, 

 F.R.S., president, in the chair. — The election of Mr. C. Roberts, 

 F.R.C.S., was announced. —Mr. W. M. Flinders Petrie read a 

 paper on the mechanical methods of the Egyptians. The author 

 exhibited several specimens of ancient Egyptian work, and 

 described the methods by which he believed them to have been 

 produced. — Mr. F. C. J. Spurrell read a paper on some palaeo- 

 lithic knapping tools and modes of using them. 



May 8.— Prof. W. H. Flower, F.R.S., president, in the 

 chair. — Mr. Frederick Bonney read a paper on some customs of 

 the aborigines of the River Darling, New South Wales. The 

 tribes with which the author was most familiar are called 

 Bungy-arlee and Parkungi. They inhabit a district within lat. 

 29°-34°. S., long. I4i°-I46° E. The country in its natural state 

 was incapable of supporting a large population, being suiiject to 

 protracted droughts, during which both food and water were 

 scarce. There is a similarity in the typical features of all the 

 Australian aborigines, but to a close observer each tribe has its 

 own peculiarities. Though ugly and unprepossessing in appear- 

 ance, they are most kind, gentle, and of quite average in- 

 telligence and morality. The aborigines of Australia are often 

 spoken of as the lowest type of humanity, but the author con- 

 sidered this to be a libel on the whole of them, and was positive 

 it is so as regards the tribes he knows best. Mr. Bonney then 

 proceeded to i;ive a description of the life history of the above- 

 mentioned tribes. — Lieut. -Col. H. H. Godwin-Austen, K.R.S., 

 read a paper on the discovery of some worked flints, cores, and 

 flakes from Blackheath, near Chilworth and Bramley, Surrey. — 

 A paper by Admiral F. S. Tremlett, F.G.S., was read, on stone 

 circles in Brittany, in which the author described three circles 

 discovered by the late Mr. James Milne, in the commune of 

 Carnac ; they had presumably been places for cremating the 

 dead, and also for depositing the urns; the greater part of the 

 latter were found inclosed in cists of quartz covered over by a 

 slab of schist, neither of which are to be found in the district. — 

 Mr. W. Galloway exhibited a skull and a number of rubbed 

 bones and other implements from the i-lands of Oronsay and 

 Colonsay, firming part of a large collection exhibited by him in 

 the Great International Fisheries Exhibition. 



Physical Society, May 12.— Prof. Clifton in the chair. — 

 New Member, Mr. A. W. Soward. — Mr. Woodward described 

 an experiment illustrating motion produced by diffusion. A 

 porous reservoir of clay containing air was suspended from one 

 end of a weighted balance beam. A glass tube projected from 

 it below and dipped into a vessel of water. A jet of hydrogen 

 gas was allowed to play on the outside of the reservoir and the 

 balance beam began to oscillate. This is an adaptation of 

 Graham's well-known experiment, and is in fact a diffusion 

 engine. Prof. Adams explained the action by the variation of 

 pressure in the reservoir set up by diffu-ion. — Mr. W. Lant 

 Carpenter read a paper on some uses of a new projection lan- 

 tern. This lantern, of German make, is applied by Mr. Pater- 

 son, and is simple in construction, cheap, and gives a good 

 image visible to a large audience. It can be used with a three- 

 wick oil lamp or the limelight. Mr. Carpenter showed a 

 number of objects on the screen. Mr. Lecky and Mr. Wood- 

 ward offered some remarks, the latter deprecating a too frequent 

 use of projection with students. — Dr. C. R. Alder Wright read 

 a paper on the electromotive force of Clark's mercur»us sulphate 

 cell and the work done during electrolysis. He described the 

 best mode of constructing Clark's standard cell. Accord- 

 ing to numerous tests, these cells vary in E.M.F. about 

 0'2 per cent. + or - among themselves. A cell properly 

 made will keep its value for about two years. It is of 

 great importance that the cell should not be worked or 

 the current reversed through it, otherwise it may permanently 

 deteriorate. The extraction of air from the paste is not very 

 essential, and boiling it is unnecessary. It is more important 

 that the solutions of zinc sulphate should be saturated. Dr. 

 Wright descrilied a cell in vacuum which is a good standard. 

 He found the E.M.F. to vary 04 per cent, between 0° and loo" 

 C. With regard to the work done in a cell, among other 

 interesting deductions, he found that in a secondary buttery the 

 larger the plates the greater the economy. In the electrolysis of 

 water the greater the surface condrnsing power of the electrodes 

 for gas the less difference of potential is required to decompo-e 

 the water. Thus with platinum electrodes a lower E.M.F. 

 serves for the electrolysis than with gold electrodes.— Prof. 

 Foster then took the chair, and Prof. Clifton read a paper on a 

 complete determination of a double convex lens by lineal 



