International Conference Held at Washington Part 21

II. The cosmic day consists of twenty-four hours, and commences at midnight of the prime meridian.

III. The earth is divided from the initial meridian into twenty-four hour-s.p.a.ces, counted in a direction contrary to the movement of the earth from _0h._ to _24h_.

We shall, then, have the following formula: T = t + R, where R represents the difference reckoned from _0h._ to _24h_. between the local time of the prime meridian and the local time of each point of the globe; T the Cosmic Time and t the local time.

The PRESIDENT. The Chair would ask the Delegate of Spain, Mr.

PASTORIN, whether he offers his resolution as an amendment to that offered by his colleague, Mr. RUIZ DEL ARBOL.

Mr. RUIZ DEL ARBOL, Delegate of Spain. Mr. Chairman, the amendment last offered is not intended to interfere with my proposition.

The PRESIDENT then put the question to the Conference upon the amendment offered by the Delegate of Spain, Mr. RUIZ DEL ARBOL.

Upon a vote being taken, the amendment was lost.

The PRESIDENT. The question now recurs upon the amendment offered by the Delegate of Spain, Mr. PASTORIN. That amendment runs as follows:

"I. We agree to choose as the prime meridian for cosmic time that meridian near which the civil day of the world commences, namely, the anti-meridian of Greenwich or Havre.

"II. The cosmic day consists of twenty-four hours, and commences at midnight of the prime meridian.

"III. The earth is divided from the initial meridian into twenty-four hour s.p.a.ces, counted in a direction contrary to the movement of the earth.

"We shall, then, have the following formula: F = A + R where R represents the difference reckoned from 0h. to 24h.

between the local time of the prime meridian and the local time of each point of the globe; F the cosmic time, and A the local time."

The PRESIDENT. In order that this amendment may be presented more clearly to the Conference, I would propose a recess for a few minutes.

If there be no objection, a recess will be taken.

No objection being made, the Conference took a recess.

The PRESIDENT having called the Conference to order stated that, unless further remarks were presented, the vote would be taken upon the resolution offered by the Delegate of Spain, Mr. PASTORIN.

No objection being made, the vote was then taken upon the amendment, and it was lost.

The PRESIDENT. The question now recurs upon the resolution offered by the Delegate of Sweden, Count LEWENHAUPT, which will again be read.

The resolution is as follows:

"The Conference recommends as initial point for the universal hour and the cosmic day the mean mid-day of Greenwich, coinciding with the moment of midnight or the beginning of the civil day at the meridian 12 hours or 180 from Greenwich. The universal hours are to be counted from 0 up to 24 hours."

Professor ADAMS, Delegate of Great Britain. Mr. President, I intended to speak on the resolution offered by the Delegate of the United States, Mr. RUTHERFURD, but the remarks which I have put together apply equally well to the amendment to that resolution now offered by the Delegate of Sweden, which is identical with one of the recommendations of the Conference at Rome, because, in fact, in my remarks I discuss these propositions alternatively. Therefore, with your permission, I will lay before you the observations which I wish to make.

I beg leave to express my entire approval of the resolution which has been laid before the Conference by Mr. RUTHERFURD. There is only one point involved in the resolution which seems to call for or even to admit of any discussion.

It appears evident that the universal day and date should coincide with the day and date of the initial meridian. The only question, therefore, which we have now to decide is, when shall this day of the initial meridian be considered to commence? And the proper answer to be given to this question does not appear to me in any degree doubtful.

In modern times it is the universal practice to reckon dates by _days_ and not by _nights_. The word "day" is used in two different significations, being sometimes applied to the period of daylight and sometimes to the period of 24 hours, including both day and night; but in whichever of these senses the word _day_ is employed, the term mid-day has one and the same signification, viz., the instant of noon or of the sun's pa.s.sage over the meridian. In the present case, where we are concerned with mean time, mid-day means the instant of mean noon, or of the pa.s.sage of the mean sun over the meridian.

Accordingly, the civil day, by which all the ordinary affairs of life are regulated, begins and ends at midnight, and has its middle or mid-day at noon.

It appears, then, most natural that the universal day should follow this example, and should begin and end at the instant of mean midnight on the initial meridian, and should have its middle at the instant of mean noon on the same meridian.

I fail, therefore, to see the force of the reasons which induced the Conference at Rome to recommend that the universal day should commence at _noon_ on the initial meridian.

The only ground for making this recommendation is that astronomers, instead of adopting the use of the civil day, like the rest of the world, are accustomed to employ a so-called astronomical day, which begins at noon. The advantage thus gained is that they avoid the necessity of changing the date in the course of the night, which is the time of their greatest activity; but this advantage is surely very small when compared with the inconvenience of having two conflicting methods of reckoning dates, and of being obliged to specify, in giving any date, which mode of reckoning is adopted. If this diversity is to disappear, it is plain that it is the astronomers who will have to yield. They are few in number compared with the rest of the world.

They are intelligent, and could make the required change without any difficulty, and with very slight or no inconvenience.

The requisite changes in the astronomical and nautical ephemerides would be easily made. As these ephemerides are published several years in advance, there would be plenty of time for navigators to become familiar with the proposed change in time-reckoning before they were called upon to employ it in their calculations.

I believe that they would soon come to think it more convenient and natural to reckon according to civil time than according to the present astronomical time. I am told that this practice is already universally adopted in keeping the log on board s.h.i.+p. To avoid any chance of mistake, it should be prominently stated on each page of the ephemerides that mean time reckoned from mean _midnight_ is kept throughout.

Whether or not astronomers agree to adopt the civil reckoning, I think we ought to adopt the instant of midnight on the initial meridian as the commencement of the universal day.

The relation between the local time at any place and the universal time would then be expressed by the simple formula:

Local time = universal time + longitude.

Whereas, if the proposition of the Roman Conference were adopted, we should have to employ the less simple formula:

Local time = universal time + longitude - 12 hours.

In recommending the mean noon at Greenwich as the commencement of the universal day and of cosmopolitan dates, the Roman Conference refers to this instant as coinciding with the instant of midnight, or with the commencement of the civil day, under the meridian situated at 12 h. or 180 from Greenwich. Now, this reference to the civil day and date on the meridian opposite to Greenwich appears not only to be unnecessary and to be wanting in simplicity, but it may also lead to ambiguity in the date, as expressed in universal days, unless this ambiguity be avoided by making an arbitrary a.s.sumption. No doubt the Greenwich mean noon of January 1 coincides with midnight on the meridian 12 h. from Greenwich, but with what midnight. What shall be its designation and the corresponding date given to the universal day?

Shall we call the instant above defined the commencement of the universal day denoted by January 1 or by January 2? Each of these dates has equal claims to be chosen, and the choice between them must clearly be an arbitrary one, and may, therefore, lead to ambiguity.

By adopting Greenwich mean midnight as the commencement of the universal day, bearing the same designation as the corresponding Greenwich civil day, all ambiguity is avoided, and there is no need to refer to the opposite meridian at all.

Those are the ideas I wish to express with regard to the commencement of the universal day.

I may mention in connection with this subject that Professor Valentiner is one of the gentlemen who were invited, a week or two ago, to attend the meetings of this Conference, in order that, if requested, they might express their opinions from a scientific standpoint upon the questions before it; but as Professor Valentiner had to leave Was.h.i.+ngton before our sessions were at an end, I thought it would be expedient to ask him for his opinion in writing upon the matter which is now pending before this Conference. He has written a letter in German, expressing his opinion. I have caused that letter to be translated into English, and if the Conference allows me I will read it.

The PRESIDENT. If there be no objection to the proposition of the Delegate of Great Britain the letter will be read.

No objection being made, Professor ADAMS continued: It is well known that Professor Valentiner is an eminent practical astronomer, and I think that any opinion coming from him on this subject, which interests astronomers very much, will be considered of great weight.

The letter runs as follows:

CHARLOTTESVILLE, VA., _October 12th, 1884_.

HONORED SIR: You had the kindness to ask me for my views as to the choice of the moment for the beginning of the day. As I cannot remain longer in Was.h.i.+ngton, I allow myself thus briefly to write to you.

When, as in the present case, the object is to introduce uniformity in the time-reckoning of the astronomical and the civil world, I am of the opinion that it is the astronomer only that must give way. For all purposes of civil life one cannot begin the day in the middle of the day-light--that is to say, in the middle of that interval during which work is prosecuted. In general it appears to me natural that the middle of the day, and not the beginning of the day, should be indicated by the highest position of the sun which governs all civil life. In fact, it would in civil life be simply impossible to bring about a change of date in the middle of the daylight. For the astronomer there certainly exist difficulties. His activity occurs mostly in the civil night, and he, therefore, has to make the change of date in the midst of his observations; and this difficulty is increased, since he almost exclusively observes according to sidereal time, so that often a computation must be made in order to ascertain whether the observations were made before or after the midnight or moment of change of date. However, this difficulty can be overcome by habit, and I believe that scarcely any doubt will occur as soon as a uniformnity of expression has established itself through the astronomical world. As regards the ephemerides, we already employ, in fact, the beginning of the date at midnight, since the places of planets and comets, are generally computed for 12 o'clock midnight of Berlin or Greenwich or other places.

But these are points that have themselves long since been discussed.

I scarcely need to say anything further. I would not hesitate for a moment to give the preference to making the change of date take place at midnight, according to civil reckoning, in order to establish a uniformity with the customs of civil life.

It, perhaps, may be important to remark that we could not introduce this change immediately, since the ephemerides are already computed and published for three or four years in advance. It would, therefore, be well to fix the epoch of change of normal dates to some distant time, such as 1890.

I remain, very respectfully yours,