Nov. 6, 1884] 



NA TURE 



ephemerides of different countries are prepared mainly 

 for the purposes of navigation, and that these ephemerides 

 are calculated generally for different meridians, should 

 charts on which longitude from Greenwich only is counted 

 come into universal use, such separate calculation would 

 become unnecessary. A certain uniformity has already 

 been arrived at, our own Nautical Almanac, the American 

 Ephcmcris, and the German Nautical Almanac being 

 all alike calculated for the Greenwich meridian, with the 

 result, however, that now a mass of information for navi- 

 gators — practically identical information — is repeated in 

 three separate works. This hardly saves labour, and it 

 seems not unreasonable to suppose, as regards the needs 

 of navigators, that one book might in some way be made 

 to serve for all. 



It may be remarked that the counting of longitude in 

 both directions up to 180° instead of continuously from o° 

 to 360 has, as regards navigation, advantages. Because, 

 when counted in both directions, a navigator or traveller, 

 in journeying round the world and changing his reckoning 

 of longitude from east to west, or from west to east, as 

 the case may be, at the same time that he makes the 

 change of one day in his date (of course somewhere near 

 the iSoth degree of longitude) will always correctly pro- 

 duce the Greenwich date, necessary when the Nautical 

 Almanac has to be referred to, by simple combination of 

 his local time and longitude, whereas if longitude be 

 reckoned from oh. to 24.I1., and the navigator makes, as 

 before, the change of one day in his date in the usual way 

 at or near the iSoth degree of longitude, which he must 

 do if his date is to be in harmony with that of the 

 countries which he will next approach (America if voyag- 

 ing east, Australia if voyaging west) it will be necessary, 

 when between longitude oh. and i2h. west, after sub- 

 tracting the longitude (always east) from the local time, to 

 further add one day, in order to produce the correct 

 Greenwich date. It will be understood that a chronometer, 

 though showing Greenwich time, does not indicate the 

 day, only hours and minutes, &c, so that a voyager has 

 to depend for the correct Greenwich date on his own 

 numeration of days and a proper consideration of his 

 longitude. 



Then as regards the question of universal time, first in 

 relation to our own country. Greenwich mean solar time, 

 or Greenwich time reckoning from midnight and counting 

 from oh. to 24I1., being adopted as the international uni- 

 versal time, is such as is shown on all railway clocks 

 throughout Great Britain, excepting that the railway 

 clocks require twelve hours to be added to their indica- 

 tions during the afternoon hours, that is, ih. railway time 

 is 13I1. universal time, and so on. Thus the time of any 

 circumstance or phenomenon occurring in Great Britain 

 will be properly given in universal time by dropping the 

 suffix a.m. or p.m., and in the afternoon adding twelve 

 hours. October 20, 9I1. a.m., and October 20, 3I1. p.m., 

 become in universal time October 20, gh., and October 20, 

 1 5h. But independently of this the counting of hours 

 from oh. to 24h. is desirable also in civil affairs generally 

 as being in itself explicit, and rendering unnecessary the 

 distinguishing a.m. and p.m. If clocks, when convenient, 

 were constructed so as to indicate hours in this way, 

 instead of counting from oh. to I2h. twice over, it would 

 tend to familiarise people with the 24-hour system with- 

 out at all forcing its use ; or the division into twelve 

 might be retained in clocks and watches, and two sets of 

 hour figures engraved. The use of the system will, how- 

 ever, extend on account of various practical advantages. 

 The plan could be introduced with benefit into railway 

 time-tables, especially those dealing with long routes, in 

 which the distinction between morning and afternoon is 

 far from explicit. Morning hours would be o, 1, 2, &c, 

 afternoon hours 12, 13, 14, &c. 



In other countries in which, as in England, the standard 

 time employed is that of some one city or observatory, 



such time similarly reckoned from midnight, and counted 

 from oh. to 24h., would be used for all internal affairs. 

 But to give the epoch of any occurrence in universal time 

 it would be necessary to subtract from the time noted the 

 longitude east from Greenwich of the city or observatory 

 whose time is used, or add thereto the longitude west. 



Whilst it is absolutely necessary for the regulation of 

 the internal affairs of a country that the time of one 

 meridian should be employed throughout, as in Great 

 Britain, it is also important that the time so used should 

 not be violently out of joint as it were with the natural 

 day. In our diminutive Great Britain no inconvenience 

 arises, as has been mentioned ; but in America, owing to 

 the vast extent of the country in an easterly and westerly 

 direction, it becomes necessary to make some arbitrary 

 division. The railway companies of Canada and the 

 United States, for regulation of the time on railways, 

 have solved the difficulty in the following way : — Four 

 different meridians being selected, those of 5, 6, 7, and 8 

 hours west of Greenwich, four separate districts are 

 created, in each of which the time of one of these 

 meridians is employed. By this means a great step in 

 the unification of time has been made, because on this 

 plan the minutes and seconds in each district are the 

 same as the minutes and seconds of Greenwich time, and 

 also therefore of universal time, the actual universal time 

 in each district being at once found if required by simply 

 adding 5, 6, 7, or 8 hours respectively to the local 

 standard time. 



But it may be asked, if the surface of the earth be 

 divided into districts counting in each, for use in civil 

 affairs, the time of some particular place or meridian con- 

 tained therein, what is the particular need of universal 

 time? The question has been already touched upon; 

 but let us illustrate. A telegram received at a telegraph 

 office in India in the afternoon for transmission to Lon- 

 don would arrive in the morning, according to the local 

 time reckoned at these places. Is there nothing here that 

 for some considerations it might not be desirable to 

 arrange differently ? Would it not be useful to have the 

 power of indicating universal time in conjunction with 

 local time, if necessary ? And so also in other affairs. 

 And in matters of science, especially the observational 

 sciences, the introduction of universal time for use when 

 required would be in many ways beneficial. When an 

 astronomer has gathered together for discussion a long 

 series of observations of, say, a new comet, made perhaps 

 at many different observatories, one of the first things that 

 he has to do is to reduce the times of observation to that 

 of one meridian. Again, observations of solar and other 

 physical phenomena cannot be properly collated unless 

 the times are reduced to one standard. Or, in magnetism, 

 on the occurrence of a great magnetic storm, how much 

 would the comparison of the records obtained at different 

 places be here also facilitated by the use of universal 

 time ? 



There might be some disinclination as regards fixed 

 observatories to give results in universal time, because of 

 the fractional difference of longitude. But in civil affairs, 

 admitting the practicability of adopting the system in- 

 augurated in America, of forming districts and employ- 

 ing as local standards of time secondary meridians dis- 

 tant from Greenwich by integral numbers of hours, as 

 before described, the indication of universal time in con- 

 junction with local standard time becomes a matter of 

 great simplicity. Objection may be made to the system 

 because of the variation, amounting to half an hour, 

 which would exist, between the natural day and the clock 

 time employed, at the extreme borders of the districts so 

 formed, but the Greenwich time long used in Cornwall 

 differs (without reckoning the effect of the equation of 

 time) twenty-three minutes from the natural time without 

 inconvenience arising. Indeed, taken in conjunction with 

 what has been done at the Washington Conference, the 



