305 



LONGITUDE AND LATITUDE. 



LORD ADVOCATE OF SCOTLAND. 



366 



metrically, which ought not to be neglected. It is well known that 

 two observers will sometimes differ several tenths of a second from 

 each other in getting the time at the same place and with the same 

 instrument. Now this personal equation, if it exist between the 

 Observers at the two places, will affect the longitude by exactly its 

 amount : hence the observers should be reversed for half the time of 

 the experiment, if possible, or their relative personal equation found by 

 comparison with each other, or at least with a third person. The 

 accuracy of a chronometrical longitude depends on the distance in time 

 between the places compared and the smoothness of the conveyance. 

 It is decidedly the best mode where the distances do not exceed 

 three or four days' journey, and where there are good carriage- 

 roads or 'steam-boats. At sea, for voyages of moderate length, the 

 Greenwich time may be taken almost entirely from chronometers; 

 and if the number be considerable, and the watches good, there is 

 little occasion for lunar distances, except for the greater caution, and 

 to be assured against any accident affecting all the timekeepers the 

 same way. 



Determination of Differences of Longitude by Rocketi. Another mode 

 of ascertaining differences of longitude is that of conveying the time 

 from one point to another by fire-signals or rockets. Thus, if a rocket 

 ia fired from a station between two observatories, and the explosion 

 noted in the lime proper to each place, the difference between the times 

 will be the difference of longitude. A chain of such signals may be 

 extended a considerable distance thus : Let the two points to be con- 

 nected be A and B, and let an observer with a chronometer be placed 

 at a, and others with rockets at a, , thus : A, a, a, 0, B. Then the 

 observers at A and B note the rockets from a and in times of their 

 respective observatories. The person stationed at a notes by his chro- 

 nometer the rockets at a and /3 (suppose J3 at 10 minutes after o), aud 

 as he observes a at the same physical moment with A, A would see 0, if 

 it were visible, just 10 minutes later than he does actually see a, and 

 therefore the explosion of $ is known in time proper to A'S observatory ; 

 but it is also seen by B at the same moment in his time, and therefore 

 the difference of longitude is obtained. In like manner, any number of 

 intermediate stations of observers and rockets may be interpolated 

 between two distant points, A and B. The relative personal eqwi 

 Hie observer at A and B must be taken into account [EQUATION, PER- 

 SONAL] both as astronomers and observers oi signals ; but the personal 

 : ' m of the intermediate .observer does not affect] the observation. 

 In this way the longitude of Paris from Greenwich was, determined. 

 (' Phil. Trans.') 



fmination of Differences of Longitude by Galvanit Signals. The 

 best method hitherto devised for determining differences of longitude, 

 is founded on the transmission of signals by galvanic electricity. This 

 method was first successfully practised in the United States of America. 

 The most obvious mode of its application consists in despatching from 

 one of the two stations to the other, a definite number of signals by 

 the telegraphic wire, the observer at the one station recording the 

 times of transmission of the signals, and the observer at the other 

 station recording the times when they are received. The opera- 

 tion is then repeated by the transmission of signals from the second 

 station to the first. The velocity of the electric fluid being supposed 

 to be sensibly instantaneous, a comparison of the local times at 

 the two stations will indicate their difference of longitude. The 

 application of this method, which has been found to give the best 

 results, consists in receiving the signals upon Saxton's recording 

 apparatus. 



Finally, the longitude and latitude of'one place from another may 

 be determined by measurements on the earth's surface, if the figure of 

 the earth be sufficiently well known. The geodesical latitudes and 

 longitudes are in many cases found not to agree with those found 

 ;itronomically, owing, an it is supposed, to some variations in the 

 density of the earth in the neighbourhood of the place of observation. 

 It ia however a convenient way of finding the latitude and longitude of 

 points near a well-established observatory, and connected by trigono- 

 metrical survey. 



Let the distance p o in feet and the bearing K o p of the point P from 

 the observatory o be known by survey, and a N be an arc of the 

 m-ridian. Then drawing P K a perpendicular to o >, r K = p o x sin of 



POK and OK=PGX cos P6K,when PK and OK are known, in feet. 

 Find the value of KG in seconds of latitude approximately by 

 supposing l"to be = 100'8 feet, aud add or subtract this, as the case 

 may be, to the latitude of a, which will give the latitude of M, the 

 middle point; call this A. Then the value in English feet of a degree 

 of latitude at M ia 



3627477 + number the logarithm of which= j 3 + 5 f/ ^ ;n x and ^ 

 value of a degree of longitude at the same parallel in English feet= 



rS'56'5161 1 [3-OS63668 



number, log= | +J " coa A | + number, log= < +log cos A. 



L -i- ^ log sin A 



With these values of a degree of latitude and longitude the distances 

 o K and p K are readily converted into arcs of latitude and longitude. 



On this subject the reader may consult the article GEODESY, and 

 the ' Encyclopedia Metropoliatana,' art. ' Figure of the Earth.' 



The solution of the problems assumed to be known in the foregoing 

 article may be found in all treatises on astronomy and in most col- 

 lections of tables of navigation. We have recommended Thomson's 

 ' Tables ' as very convenient, and sufficiently accurate for the traveller 

 and navigator, but any tables and methods which a man has become 

 accustomed to will do. It would require too much space to give reasons 

 and explanations for the opinions here advanced, but we will give two 

 or three recommendations which few observers will regret to have 

 followed. The first is to make, when practicable, large masses of 

 careful and unhurried observations, and especially to observe the rules 

 given above for nullifying instrumental error, by making such observa- 

 tions that a given error will have contrary effects in the result. 

 Secondly, to be very careful in selecting their instruments and their 

 timekeepers, which should come from good makers, and be carefully 

 tried before starting, especially at such temperatures as the traveller 

 may expect to meet with. A chronometer which is excellent for a polar 

 expedition may be an indifferent watch on the Tigris or in the interior 

 of Africa, and vice versa. For any overland expedition three pocket 

 chronometers should at least be taken, and the number must be 

 increased according to the length, the difficulty, and the importance of 

 the journey, and a liberal allowance made for stoppages, changes of 

 rate, accidents, &c. : a belt of half a dozen chronometers would scarcely 

 be felt to be an inconvenience. Lastly, if the traveller's object be 

 chiefly that of determining exact positions, he should ba careful to 

 determine the longitudes of all his principal points by solar eclipses or 

 occultations of fixed stars by the moon, if he cannot carry and fix a 

 transit. At these points he should determine the rates of his chrono- 

 meters for a new departure, and determine as much of the country as 

 circumstances will allow by journeys of ten days or a fortnight, 

 returning to the same place. When the principal points are well fixed 

 (we speak of longitudes, for good latitudes may be got with almost any 

 instrument, or by any person), the chronometers will fix every halting- 

 place where the time is observed, and this may be got in a few minutes 

 any fine night or morning or afternoon ; and then the itineraries, 

 compass bearings, marches, &c.,and all the loose information on which 

 too much of our geography is founded, will furnish valuable details in 

 the proper place. The necessary apparatus is not very expensive or 

 cumbrous, and with a little practice can be managed by a moderately 

 intelligent and methodical person. 



LOOM. [WEAVING.] 



LOPHINE (C.^H^N,) is one of the bases derived from the oil of 

 bitter almonds. It is formed when benzoline is distilled. Ammonia 

 is given off, and lophine is left undissolved. It is soluble in alcohol 

 with acids, aud precipitated again by ammonia. It occurs in the form 

 of fine silky crystals, and forms salts with acids, which are however 

 not very stable. 



LORD ADVOCATE OF SCOTLAND. This is the peculiar 

 appellation of the senior standing counsel for the crown in Scotland. 

 The regular series of such officers cannot be carried to an earlier 

 date than the end of the 15th century. Previous to that time, in- 

 dictments seem to have been under the superintendence of the 

 clerk of court, or justice clerk [JUSTICE CLERK]; and for pro- 

 secutions before the parliament, we find sometimes the chancellor, 

 sometimes the clerk-register, and at other times a special counsel for 

 the crown. 



The earliest standing " Advocate," and with whom the series pro- 

 perly begins, was Sir John de Ros of Mountgreenan, in the county of 

 Ayr, an individual well known both in the politics and literature of his 

 time, and one of the poets commemorated by Dunbar. When the 

 Court of Session was erected, Sir Adam Otterbuni of Auldhame was 

 king's advocate, and was not only privileged to plead within the bar, 

 but actually nominated one of the judges of the court. It was from 

 this circumstance he acquired the style of Lord Advocate (Pitcairn's 

 Criminal Trials, Stat. 1587, c. 115.). In 1610, he had the additional 

 style of " Right Honourable." (Act of Sederunt, 17th Nov., 1610.) It 

 was, however, in the time of Sir Thomas Hope (founder of the noble 

 family of Hopetoun, and others) that the office acquired the vast politi- 

 cal importance which has in modern times belonged to it. This arose not 

 less from the subtle and ambitious character of that famous person, 

 than from the circumstance of the king's removal to the throne of 



