Dec. 5, 1884.] 



♦ KNOWLEDGE ♦ 



461 



I 



In what, then, it may be asked, does the importance of 

 the recent change consist i The astronomer and the geo- 

 grapher do not need to ask the question, knowing as they 

 do the multitudinous inconveniences which arise from the 

 use, in the astronomical computations, and the geographical 

 charts made in different countries, of tlio longitudes of 

 Greenwich, Vienna, Berlin, Paris, Washington, and so 

 forth. I take up, for example, in the old time of the con- 

 troversy about the transit of Venus, a treatise or paper 

 written by Puiseux at Paris, or by Newcomb at Washing- 

 ion, and I find that before I can compai-e properly the 

 results deduced or discussed by the French or American 

 astronomer with my own, or with others dealt with by 

 English astronomers, I must translate the French or 

 American longitudes and times into Greenwich longitudes 

 and times. Even iu the case of a single treatise, the time 

 thus wasted (there is no other word for it) is considerable ; 

 but when a great number of such works, on different 

 astronomical subjects, pass through an astronomer's hands 

 weekly or monthly, as is the case with nie, the nuisance 

 becomes quite serious ; and when we remember that this 

 is so in the case of one person alone, we see how large the 

 total waste of time and trouble thus arising must neces- 

 sarily be. 



The geographer is similarly annoyed. In comparing 

 French, German, or American maps with English maps, or 

 geographical statements by geographers of other countries 

 with similar ones made in England, the geographer finds 

 that every detail depending on longitude has to be corrected 

 or translated before the full significance of the foreign 

 charts or statements can be appreciated. 



In fact, this question of a meridian of reference may be 

 regarded as affecting our view of the earth from without, 

 as it were, more importantly than the view we take of the 

 earth as residents in this or that part of her surface. It is 

 the earth as a rotating planet which has now been definitely 

 marked for reference, so that all astronomers and all geo- 

 graphers measure from one and the same mark, not each 

 8et from a mark of their own. Just as astronomers use a 

 fixed meridianal marking on Mars by which to time the 

 rotations of the planet, so in future will astronomers and 

 geographers act with regard to the earth. Strange that 

 they should have assigned a fixed meridian to a planet 

 many millions of miles away, many years before they 

 assigned a fixed meridian to their own planetary home ! 



It may be asked whether the adoption of a fixed 

 meridian for the whole earth will affect the question many 

 find so perplexing, as to what day of the week it is at parti- 

 cular places, and at particular times. Here it is to be 

 noticed that the usage of astronomers and the usage of 

 business folk mast of necessity difler. To the astronomer 

 there will now be, what hitherto there has not been, a 

 definite series of days, the same all over the world. What 

 people in England call, for instance, November 17, viz., 

 the interval of time between midnight and midnight on 

 either side of that day whose middle is noon November 17, 

 has been for the English astronomer, and will hereafter be 

 for the astronomers of all countries, divisable into the last 

 twelve hours of November 16 (which ends for the astrono- 

 mer at noon November 17) and the first twelve hours of 

 November 17, whose remaining twelve hours, numbered 

 from 13 to 21, end at noon November 18, civil time. 

 So, all round the year, — December 25, for instance, in 

 astronomical time, will include tor all astronomers, the 

 twenty-four hours from December 25, 12 noon Greenwich 

 mean time, to 12 noon Greenwich mean time, December 2G. 

 But as to what day of the week it is at any particular 

 place and time, the difficulty, which many imagine to 

 «xist only along the meridian half-way round the earth. 



west or east of Greenwich, has always existed, and will 

 continue to exist, all over the earth. It is true that when 

 we travel westwards or eastwards from Greenwich, we 

 have to make a change of a full day, one way or the 

 other, when near the meridian, which lies 180 deg. east 

 (or west) of Greenwich. But that is only because we 

 have not made the necessary partial change at each suc- 

 cessive stage of our journey west or east of Greenwich. 

 Or it might, perhaps, be rather said that small partial 

 changes are made stage by stage in passing westwards or 

 eastwards, which amount to half a day where two voyagers 

 travelling westwardly and eastwardly at equal rates 

 would meet ; and these changes being in opposite direc- 

 tions, the two half days must be made into a whole day 

 at the place where the voyagers cross each other, the west- 

 wardly voyager now taking the days (one ahead of those 

 he had been using) of the eastwardly voyager, and vice 

 versd. But the difficulty as to the day of the week exists 

 all along, and is actually felt (which is different) wherever 

 we pass across a line dividing two regions where diflerent 

 local time is u.sed. Thus, suppose we are on a train 

 travelling westwards from New York, and pass, at half- 

 past twelve at night, a place where, along that railroad 

 line, the change of an hour is made. It is, let us say, 

 Tuesday morning early (half-an-hour after midnight) before 

 we pass that place ; but so soon as we have passed the place 

 of change, it is no longer Tuesday morning but Monday 

 — night — half-past 11p.m. By passing to and fro across 

 the line of change, at any hour between 12 midnight and 

 1 a.m., for the eastward region, or (which is the same thing) 

 between 11 p.m. and 12 midnight for the westward region, 

 we can make the day of the week change as often as we 

 please, or have any number of Mondays and Tuesdays, 

 Tuesdays and Wednesdays, itc. (as the case may be), 

 in the course of a single hour. But the diflerence 

 of day in such a case as this is a matter of no mo- 

 ment, and needs no correction, whereas it would be a 

 matter of serious moment if every one who had circled 

 around the earth either eastward or westward remained a 

 whole day behind or in advance of those among whom he 

 lived. It is obvious that as the westward traveller keeps 

 on adding hour after hour to his time, he must add a fuU 

 day by the time he has gone completely round, and unless 

 he dropped a day somewhere, he would be a day behind the 

 friends whom he had left at home by the time he rejoined 

 them. The opposite change must be made by a traveller 

 going eastwards ; and clearly the proper place for the 

 change is when either is half-way round ; for by making 

 it there the discrepancy never exceeds half a day. 



It is noteworthy, however, that the only place where the 

 day exactly corresponds with the Greenwich astronomical 

 day is along the meridian just westward of but touching 

 the meridian farthest from Greenwich. Thus, the astro- 

 nomical day — November Nth — runs from November 17th 

 noon to November 18th noon (Greenwich mean time) ; 

 and at a place just short of 180° west of Greenwich 

 November 17th also begins at noon November 17th (Green- 

 wich mean time) and ends at noon November 18th. — New- 

 castle Weekly Chronicle. 



Is the December number of the " Miscellanea Genealogioa et 

 Heraldica" there is the facsimile of a very rare, perhaps unique, 

 funeral card ; the original is at Hardwick, among the collections 

 formed by Sir John Cullum, Bart. This card entitled the bearer 

 " to accompany the Corps of Mr. Thomas Moodij, from Armourers- 

 Ball in Coleman-Street, to the Burying Ground on Bun-Hill, on 

 Friday, May the ISth, 171C, by Five of the Clock in the Afternoon 

 precisely. — And bring this Ticket with you." Although the Bunhill 

 Fields Registers corroborate the date of Mr. Moody's burial, y«t 

 there is no monument now in existence to his niemorj-. 



