Sept. lo, 1874] 



NATURE 



389 



pofiticn of liinetic equilibrium of tbc conipaES at tbat instant is 

 the position in which it would rest under the magnetic forces and 

 a force of afpaiint gi-avily equal to the resultant of gw and a 

 force a w in the direction opposite to that of a. Now the weight 

 of the compass is so great, and its centre of gravity so low, that 

 the level of the card is scarcely aflecled sensibly by the greatest 

 magnetic couple experienced by the needles.* Hence, in kinetic 

 equilibrium the plane of the compass card is sensibly perpen- 

 dicular to the direction of the " apparent gravity" defined above; 

 and the magnetic axis of the needlts is the direction of the 

 resultant of the ccniponerts in this plane of the magnetic forces 

 of eaith and ship. Hence it is simply through the aj'parait iez'd 

 at the place in the ship occupied by the compafs diflerirg from 

 the true gravitation level that the problem of the kinetic equili- 

 brium position of the ccmpass in a rolling ship differs from 

 the problem of the heeling error referred to above. That we 

 may see the essential peculiarities of cur present problem, let 

 there be no magnetic force of the ship herself or cargo. The 

 kinetic equilibrium position of the magnetic axis of the compass 

 will be simply the line of the component of terrestrial magnetic 

 force in the plane of the apparent level. The author then 

 investigates, by a mathematical process, an expression for 

 "the kinetic equilibrium error," which is so named in order to 

 distinguish it from the error actually exhibited by the compass. 

 The kinetic equilibrium error is exactly the error which would 

 be shown by an ideal compass with infinitely short period of 

 vibration. A light quick needle (either with silk fibre suspen- 

 sion or supported on a point in the ordinary way), having a 

 period of not more than about two seconds, shows the rolling 

 error very beautifully, taking at every instant almost exactly the 

 position of kinetic equilibrium. Sir W. Thomson has thus found 

 it so great in a small wooden sailing vessel that it became very 

 difficult to make exact observations with the quick compass, 

 either in the Firth of Clyde or out at sea on the Atlantic, unless 

 when the sea was except ion.ally smooth. The kinetic theory of 

 forced oscillations is readily applied to calculate, whether for a 

 wooden or an iron .ship, the actual "rolling error" of the com- 

 pass from the " kinetic equilibrium error," but the author remarks 

 that it would extend the present communication too far to enter 

 on details of this solution. For the present it is enough to fay 

 that r.o admissible degree of viscous resistrnce can make the 

 rolling error small enough for practical convenience, unle.'-s also 

 the period of the compass is longer than that of any consideiabie 

 rolling to which the ship may be subjected. Probably a period 

 of from fifteen to twenty seconds (such as an ordinaiy compass 

 has) may be found necessary for general use at sea ; and it 

 bf comes an important practical question how this is best to be 

 obtained, consistently with the smallness of the compass needles 

 necessary for a thoroughly satisfactory application of the system 

 of magnetic correctors, by which the Astronomer Royal proposed 

 to cause the compass on an iron ship to point correct magnetic 

 courses on all points. 



On the Spiclrum of Coggia^s Comet, by Dr. Huggins. — The 

 new point noticed in this comn unication was that the bands 

 ot the comet were so far shifted as to indicate— supposing there 

 really was carbon in the comet — that the itlattvc motion of the 

 approach ol the comet to the earth was forty-six miles per second. 

 The comet really, however, approached tire earth at the rate of 

 twenty-four miles per second ; ai d it was therefore ur.ccrtain 

 whether the whole or part of the difference in this velocity was 

 due to the motion of matter within the comet. Tie brighter 

 portion of the head of the comet was due evidently to a larger 

 I'roportion of the matter giving a contirucus specirum. It 

 seemed probable, therefore, to tlie author that the nucleus was 

 solid, heated by the sun and throwing out matter which formed 

 the coma and tail ; and part of this was in a g.-se(us form, 

 giving the spectra of bright lines. The other portion (xisted 

 probably in small incanilescent panicles ; the polariscope show- 

 ing that certainly not more than one-fifth of the whole Jight was 

 reflected solar light. 



further Exferiincitts on Lig^Jit ic/,/; eirciilar/y itiled fiaUs of 

 glass, by Phihp Braham, F.C.S. 



Interposing plates of ciicularly ruled glass in the beam of 

 light from aheliostat, the rings of colour are in the same order by 

 retlection and refraction, the red in both ca.ses being outward. 



Observing the rings of reflected colour when the univiled sur- 

 face of the glass is away (rcmr the he'iostat, daik bands make 

 their appear;:nce concentric with the coloured lings, if tlie surface 



* Generally no adjusling counteri»oise tor tlie compass i* required when a 

 ship goes from extreme north to extreme south magnetic latitudes, 1 



of the rulings is at right angles to the direction of the beam, and 

 on altering the angle of the ruled plate the dark bands expand 

 until they intersect the coloured circles, and also appear con- 

 siderably beyond them. 



Placing a polished plate of speculum metal in contact with the 

 ruled surface of the glass increases the intensity of the dark 

 bands, and by adjustment shows that according to the distance 

 of the reflecting surface from the ruled, the number and thick- 

 ness of the daik batrds are increased or diminished. 



A description was given of the heliostat used, the reflector 

 being a rectangular glass prism. 



SECTION B— Chemical Science 

 The Chemical Comfosi/iou of Jute Fibre, by Prof. Hodges. — 



The jute plant belongs to the family Tiliaceas. The Corchorus 



eapsiilaris and C. olitorius are both cultivated. 



The structure of the filjre is different from that of other textile 



fibres, the central space being very irregular, varying from the 



thickness of a line to a considerable width. 



Ey the action of anihne sulphate, jute fibre becomes of a golden 



yellow colour, whereby it is distinguished from hemp and flax. 



The following is the analysis of jute fibre ; — 



Wax and fatty matter soluble in ether ... ... o'235 



Tannic acid and colouring matter soluble in alcohol I'I35 



Sugar, pectine, &c 2-427 



Soluble nitiogenised matters ... 0512 



Insoluble ,, ,, ... ... ... ... 2'433 



Inorganic matter combined with fibre loio 



Cellular fibn 



92-24 



Ni'rogen in original fibre ... ... ... ... 0-291 



Nitiogen in fibre after treatment with solvents ... 0-210 



Milhyl-theline, by Prof. Ctum Brown ard Dr. E. A. Letts. — 



Ey the acion of bromacetic acid en methyl-sulphide, miclhyl- 



thetine hydrobromate is produced. By the action of moist 



siher oxide on this hjdrobiomate, silver bromide is found, and 



by the further cautious addition of the hydrobromate, the silver 



ri maining in solution is removed. By evaporation, ciyslals of the 



basemethyl-ihetineaie foinred with one molecule of water. This 



crys'allised base might I e represented by the structuial fuimula : — 



S(CH3), , 



'I 

 H-C-COO }+ H,,0. 



I'l i " 



Ey the decomposition of the tulphate of methyl-tlietnre by 

 mians of barium carbonate, the base may also be prepared. 



This substance, methyl-thetine, has both a basic and an acid 

 character ; with hydrochloric acid it forms a hydrochloride, from 

 which the double platinum chloride has been prepared. A 

 double lead compound containing 2PbBr2 has also been prepared. 



The action ef iodacetic acid on methyl-sulphide does rot give 

 rise to the formation of methyl-thetine hydriodate, as might have 

 leen expected ; but various substances are foi.med, among which 

 js trimethyl-sulphine iodide. 



Exfct imctits on Iii'^h Pressures, by Dr. Andrews, F. R. S. 



The author entered into full details of the methods of preparing 

 and us^ng his well-known tubes for the production of high pres- 

 sures. If a mixture of nitrogen and carbonic acid be subjected 

 ^o high pressures (to 290 atmospheres), no trace of liquid is 

 produced. 



On the Latent Heat of Liqnefied Gases, by J. Dewar, F.R.S.E. 

 — The author has deduced a formula for calculating the latent 

 heat of a gas from the known tension of that gas. The results of 

 this investigation have already been communicated to Section A, 



On Spontaneous Generation from a Chemical Point of Vino, 

 by Dr. Debus, F.R.S. — To the question, "Has Nature ever pro- 

 duced organic substances from strictly inorganic materials?" 

 Chemistry (.according to the author) arrswers, "No ! " 



On the Estimation of Fhosphoric Acid in Pyrophosphate oj 

 Magnesia, \,y Mr. Ogilvie.— 1 he author's experiments lead him 

 to conclude that this process cannot be relied upon unless taken 

 in conjunction with some other, such as the Molybdate process. 

 The influence of ,1 great excess of magnesia, of ammonic oxalate. 



