astronomical day will be considered at this observatory as beginning at midnight, corresponding to the civil date; and that the records of all observations taken on and after that date will be made in conformity with that recommendation. Very respectfully, Prof. S. NEWCOMB, U. S. N., S. R. FRANKLIN, Commodore, Superintendent. Superintendent of Nautical Almanac, Washington, D. C. No. 4. NAUTICAL ALMANAC OFFICE, NAVY DEPARTMENT, SIR: I have the honor to submit the following remarks upon those conclusions of the recent International Meridian Conference which affect the work of this office. It is gratifying to notice that the conclusions alluded to, so far as their main features are concerned, are in substantial accord with the practice in this country, and with the system which has been adopted in the construction of the American Ephemeris and Nautical Almanac. On this system longitude and times are counted from Greenwich, except when, for purely local astronomical purposes, the meridian of Washington may be more convenient; and all longitudes are counted east and west to the anti-meridian of Greenwich. The recommendations which it is the object of this communication to consider more in detail are the following: (1) The Conference expresses the hope that as soon as may be practical the astronomical and nautical days will be arranged everywhere to begin at mean midnight. (2) That east longitudes shall be counted as plus and west longitudes as minus. The first of these recommendations proposes a change in the method of counting astronomical time which has come down to us from antiquity, and which is now universal among astronomers. The practice of taking noon as the moment from which the hours were to be counted originated with Ptolemy. This practice is not, as some distinguished members of the Conference seem to have supposed, based solely upon the inconvenience to the astronomer of changing his day at midnight, but was adopted because it was the most natural method of measuring solar time. At any one place solar time is measured by the motion of the sun, and is expressed by the sun's hour angle. By uniform custom hour angles are reckoned from the meridian of the place, and thus by a natural process the solar day is counted from the moment at which the sun passes over the meridian of the place or over the standard meridian. For the same reason sidereal time is counted from the moment at which the vernal equinox passes over the meridian of the place, and thus the two times correspond to the relation between the sun and the equinox. It would appear that the Conference adopted the recommendation under the impression that the change would involve nothing more than the current method of reckoning time among astronomers, and could therefore be made without serious inconvenience. A more mature consideration than time permitted the Conference to devote to the subject would, I am persuaded, have led that distinguished body to a different conclusion. A change in the system of reckoning astronomical time is not merely a change of habit, such as a new method of counting time in civil life would be, but a change in the whole literature and teaching of the subject. The existing system permeates all the volumes of ephemerides and observations which fill the library of the astronomer. All his text books, all his teachings, his tables, his formulæ, and his habits of calculation are based on this system. To change the system will involve a change in many of the precepts and methods laid down in his text books. But this would only be the beginning of the confusion. Astronomical observations and ephemerides are made and printed not only for the present time, but for future generations and for future centuries. If the system is changed as proposed the astronomers of future generations who refer to these publications must bear the change in mind in order not to misinterpret the data before them. The case will be yet worse if the change is not made by all the ephemerides and astronomers at the same time epoch. It will then be necessary for the astronomers of the twentieth century, using ephemerides and observations of the present, to know, remember, and have constantly in mind a certain date different in each case at which the change was made. For example, if, as is officially announced, the Naval Observatory introduces the new system on January 1, 1885, then there will be for several years a lack of correspondence between the system of that establishment and the system of the American Ephemeris, which is prepared four years in advance. It is difficult to present to others than astronomers who have made use of published observations the confusion, embarrassments, and mistakes that will arise to their successors from the change. The case can be illustrated perhaps by saying that it is of the same kind as-though in less degree than-the confusion that would arise to readers and historians in the future if we should reverse or alter the meaning of a number of important words in our language with a result that the future reader would not know what the words meant unless he noticed at what date the book was printed. The words would mean one thing if printed before the date of change and another if printed after. It is worthy of attention that even the republican Government of France in 1790, which adopted a new calendar, did not venture to change the old system in its astronomical ephemeris. I see no advantage in the change to compensate for this confusion. If astronomical ephemerides were in common use by those who are neither navigators nor astronomers the case would be different. But, as a matter of fact, no one uses these publications except those who are familiar with the method of reckoning time, and the change from astronomical to civil time is so simple as to cause no trouble whatever. The change will affect the navigator as well as the astronomer. Whether the navigator should commence his day at noon or midnight, it is certain that he must determine his latitude from the sun at noon. The present system of counting the day from noon enables him to do this in a simple manner, since he changes his own noon into the astronomical period by the simple addition or subtraction of his longitude. To introduce any change whatever into the habits of calculation of uneducated men is a slow and difficult process, and is the more difficult when a complex system is to be substituted for a simple one. I am decidedly of the opinion that any attempt to change the form of printing astronomical ephemerides for the use of our navigators would meet with objections so strong that they could not be practically overcome. The second conclusion which I wish to consider is that which proposes to reverse our method of assigning algebraic signs to the longitudes by counting east longitudes as plus and west longitudes as minus. The present system was adopted some forty years ago in Germany as being the most natural, because longitude was measured upon the earth by the apparent motion of the sun and stars from east to west, and it seemed most natural to count the direction of this motion as algebraically positive. This system has been adopted in the American Ephemeris since its origin, and all its tables and formulas which involve the application of longitudes have been constructed on this principle. To reverse this method will cause error and confusion to every one using the Ephemeris without, as far as I can see, the slightest compensating advantages. I am therefore of opinion that it should not be adopted. I respectfully submit that in view of these considerations no change should be made in the change of reckoning time employed in the publications of this office until, by some international arrangement, a common date shall be fixed by all nations for the change. An appendix to this communication gives the changes which will be necessary in the Nautical Almanac and Ephemeris if the new system is adopted. Very respectfully, your obedient servant, Hon. W. E. CHANDLER, S. NEWCOMB, Superintendent Nautical Almanac Office. Secretary of the Navy, Navy Department, Washington, D. C. Respectfully forwarded. APPENDIX. J. G. WALKER, Chief of Bureau of Navigation. List of changes in the Nautical Almanac required when the astronomical day is reckoned from midnight. Page 1 of each month: The numbers on this page being given for Greenwich apparent noon, the question whether they shall remain unchanged or be given for Greenwich apparent midnight will have to be decided by competent authority. 2. Page 2 of each month to correspond with the new mode of reckoning these numbers would be given for mean midnight, which would change the whole page. Page 3 of each month: Nearly the same remark applies to these pages as to page When the change is made there will be a discontinuity of half a day in the comparison of the sun's longitudes before and after the change. Page 4 to correspond strictly to the new reckoning, the columns noon and midnight on this page would have to be interchanged. This might lead to errors on the part of the computer accustomed to the old system inadvertently forgetting the change which had been made. If not made the system would be a mixed one. Pages 5 to 12: All the numbers on these pages will be differently arranged when the hours are counted from midnight. Pages 13 to 18: The lunar distances will have to be given for midnight on the first column of the left-hand pages, and for noon on the first column of the right-hand pages, thus reversing the placing of the numbers on the two pages. Planetary ephemerides: These will naturally have to be given for midnight instead of noon, and the signification of all the numbers will therefore be different. There will also be a discontinuity of half a day in the progression of the series of epochs at the time the change is made. Moon's longitude and latitude: The indications of the times given in this part of the Ephemeris will be altered by half a day. The result would be that a computer inadvertently forgetting the change would take out a result half a day in error. Sidereal time of mean noon: Wherever this quantity was given throughout the Ephemeris it would, on the new system, have to be replaced by the sidereal time of mean midnight. Transit ephemerides: These would remain unaltered except the column of mean time of transit, which would be changed by 12 hours. Changes of nearly the same kind as in the planetary ephemerides would have to be made in giving the predictions of phenomena. No. 5. UNITED STATES NAVAL OBSERVATORY, Washington, December 11, 1884. SIR: Referring to the letter of Professor Newcomb, concerning the resolution of the late International Meridian Conference on the subject of the change of the astronomical date, so as to make the midnight of Greenwich 0 hours, instead of noon as at present, I have the honor to submit the following considerations as those which appear to me to be sufficient to justify the issuance of the order I have recently given to begin the reform at the commencement of the coming year. The order referred to (a copy of which is here with inclosed) was not issued without due consideration by the Board of which Professor Hall is a member; not without a knowledge on my part of the views of such a distinguished astronomer as Professor Adams, of England, as well as of those of other members of the Conference. A reference to the proceedings of the Conference shows that its recommendation on this point was unanimous. It has been publicly announced in Nature that the Astronomer Royal of England proposes to make the change on the same date as that directed by me; this has been confirmed by a telegram received from him by me. So far as the counting of astronomical time from antiquity is concerned, it is the argument of conservatism which desires no change in an existing order of affairs; yet, assenting to this argument, we might refer to a still remoter antiquity-to the time, not of Ptolemy, but of Hipparchus, the "founder of astronomy," who reckoned the twenty-four hours from midnight to midnight, just as the Conference has proposed. While it is unquestionably true that some confusion may occur, yet the liability to it will be almost entirely with the astronomer, who, through his superior education and training, could easily avoid it by careful attention to the ephemerides he was using. During the years of change, before the ephemerides are constructed in accordance with the new method, it will only be necessary to place at the head of each page of recorded observations the note that the time is reckoned from midnight, to call attention to the fact, and thus obviate the danger of error. It is an undeniable fact that the educated navigator finds the conversion of time a simple matter, yet experience has demonstrated that to the mariner who is not possessed of a mathematical education there is a decided liability to the confusion which is so greatly deprecated by all who are interested in this subject. I believe that to all navigators, at least to all English-speaking ones, the new method will prove itself decidedly advantageous. As is well known, for many years navigators kept sea time, by which the day was considered to begin at noon, preceding the civil day by twelve and the astronomical date by twenty-four hours. The change to civil time now kept on board ship was effected readily and without friction, so that the recommendation of the Conference regarding the commencement of the nautical day has already been largely anticipated. The navigator is concerned not with his longitude but with his Greenwich time, having obtained which he can take from the Nautical Almanac the data he seeks, whether given for noon or midnight, and when the ephemerides shall have been made to conform to the new system there will be one time in common use by all the world. It seems to me eminently proper that the nation which called the Conference should be among the first to adopt its recommendations, and while it might possibly be better to wait until an entire agreement has been entered into by the astronomers of all nations, yet the fact that the first and most conservative observatory in the world has acceded to this proposal of the Conference would seem to be a sufficient reason why we should not wait for further developments. In deference, however, to the views so well advanced by Professor Newcomb, and in view of the fact that the President has recently transmitted the proceedings of the Conference to Congress, as well also of the desirability of securing uniformity among the astronomers of our own country at least, I have suspended the execution of the order for the present with the view of communicating with those engaged in kindred work in order to ascertain their sentiments on the subject. Professor Newcomb's letter is herewith returned. Does Greenwich begin astronomical day midnight January 1 next? FRANKLIN, [Telegram.] LONDON. (Received at 10.08 a. m., December 11, 1884.) To FRANKLIN, Observatory, Washington: We begin January 1 reckoning from midnight for internal use, awaiting official communication before introducing generally. No. 7. [Circular.] CHRISTIE, Greenwich. UNITED STATES NAVAL OBSERVATORY, SIR: At the recent International Meridian Conference, as you doubtless well know, it was recommended that as soon as possible the astronomical and nautical days be considered as beginning at mean midnight. As to the nautical day, that has for many years been so reckoned in our naval service. With regard to the astronomical date, I am informed by the Astronomer Royal that he intends to "begin the day at midnight January 1, for internal use, awaiting official communication before introducing generally." As it is very desirable to secure uniformity of action among the astronomers of our own country in this matter, before finally deciding to begin the new method of reckoning at this observatory, I respectfully request that you will favor me with your views on the subject; especially as regards the date on which it would be best to introduc the new system. Yours, very respectfully, S. R. FRANKLIN, Commodore, Superintendent. No. 8. LEANDER MCCORMICK OBSERVATORY, University of Virginia, December 18, 1884. DEAR SIR: In my opinion the change of the astronomical day so as to correspond with the civil day should be made January 1 (midnight before 1885), but not merely for internal purposes. Will you be kind enough to inform me as to your decision when made, so that we may conform to your custom. Very truly yours, Commodore S. R. FRANKLIN, U. S. N., Superintendent Naval Observatory, Washington, D. C. ORMOND STONE. No. 9. YALE COLLEGE OBSERVATORY DEAR SIR: I am in receipt of your favor of the 15th instant, in which our views are invited upon the subject of the proposed change by which astronomical and nautical days shall be made to begin at midnight instead of noon; also, as regards the date on which it would be best to introduce the new system. We think that the change proposed is a desirable one, and we believe that it will commend itself to astronomers generally. We see no reason why any observatory may not in its internal management introduce the change at any date most convenient to itself. The change, or even the attempts to change, will of necessity cause confusion for several years. It is the duty of astronomers to make the inconvenience as little as possible. We think therefore that in every communication from an observatory to the scientific or to the general public in which the hour and day of any event shall be stated, the words civil reckoning (or something equivalent) should be added in case the hour shall be reckoned from midnight. On the other hand, some corresponding statement should be made in case the hour shall be reckoned from noon. This practice of defining the time should be adopted immediately, and adhered to for many years to come. I have the honor to be your obedient servant, H. A. NEWTON, Secretary of Board of Managers of the Observatory in Yale College. Commodore S. R. FRANKLIN, U. S. N., Superintendent United States Naval Observatory. No. 10. HARVARD COLLEGE OBSERVATORY, DEAR SIR: Your letter of December 15, relating to the proposed change in the beginning of the astronomical day has been received. I regard a general agreement upon the subject among astronomers as of greater importance than the mode of reckoning itself, and I shall be glad to promote such an agreement by any means in my power. The question of most immediate importance which is connected with the subject relates to the dates of discovery and observation given in astronomical telegrams. I have written to Dr. Kruger upon this point, and hope to have an answer from him soon. In the publications of this observatory, the dates will be in Greenwich mean time, with whatever signification that term may actually bear among astronomers generally. Yours, respectfully, Commodore S. R. FRANKLIN, United States Naval Observatory. EDWARD C. PICKERING. |