Prof. Abbe, Delegate of the United States, stated that the Delegate of France, Mr. Janssen, had made a very important proposition to the Conference: That the meridian adopted should be a neutral one. He said that he had endeavored to determine what a neutral meridian is. On what principle shall the Conference fix upon a neutral meridian, and what is a neutral meridian? Shall it be historical, geographical, scientific, or arithmetical? In what way shall it be fixed upon? He looked back a little into the history of an important system adopted some years ago. France determined to give us a neutral system of weights and measures, and the world now thanks her for it. She determined that the base of this neutral system should be the ten-millionth part of a quadrant of the meridian. She fixed it by measurement, and to-day we use the metre as the standard in all important scientific work; but is that metre part of a neutral system? Is our metric system neutral? It was intended to be, but it is not; we are using a French system. Had the English, or the Germans, or the Americans taken the ten-millionth part of the quadrant of the meridian, they would have arrived at a slightly different measure, and there would have been an English, a German, and an American measure. We are using the French metric system. It was intended to be a neutral system, but it is a French system. We adopt it because it deserves our admiration, but it is not a neutral system. The various nations of the world might meet and agree upon some slight modification of this metric system which would agree with the results of all scientific investigations, and thus make it international instead of French; but we do not care to do that, and are willing to adopt one system, taking the standard of Paris as our standard. How shall we determine a neutral system of longitude? The expression "neutral system of longitude" is a myth, a fancy, a piece of poetry, unless you can tell precisely how to do it. He would vote for a neutral system if the French representatives can tell the Conference clearly how to decide that it is neutral, and satisfy them that it is not national in any way.
Mr. Janssen, Delegate of France, said:
I perfectly understand the objection of my honorable colleague, Prof. Abbe. He asks what is a neutral meridian, and adds that the metre itself does not appear to him to be a neutral measure, but to be a French measure. He relies upon the consideration that if the English, the Americans, and Germans, in adopting a definition of the metre, had measured it for themselves, they would have arrived each at a slightly different result, which would have given us an English, American, and German metre; nevertheless, he adds, we use the French metre, because we find it so admirable.
I would answer, first, that the metre, as far as the measure is derived from the dimensions of the earth, is not French, and it was precisely to take away this character of nationality that those who fixed on the metre sought to establish it on the dimensions of the earth itself. What is French is the particular metre of our national archives, which exhibits a very slight difference from that which our actual geodesy would have given us. Also, I think that if, at the time of the adoption of the Convention du Mêtre, in which the nations of Europe participated, we had slightly changed the length of our standard to make it agree with the result of actual geodetic measurements, we should have done an excellent thing in depriving this measure of any shadow of nationality. I agree with my honorable colleague that if a few slight changes adopted by common accord could perfect the metrical system, we French ought to have no motive for opposing it. We have the honor of having invented a system of measures which, being based upon considerations of a purely scientific nature, has been accepted by all. Therefore if it can be said with truth that the metre of the Archives of Paris is French, (not intentionally, but because it bears the mark of an error of French origin,) it is an international metre, by the same title that the discovery of the satellites of Mars made by my friend, Prof. Asaph Hall, whom I have the pleasure of seeing here, is scientific and of a universal nature. The metre—equal to the ten-millionth part of the distance from the equator to the pole—is no more French than that distance itself, and, nevertheless, if the Americans, English, or Germans had measured it, they would each have arrived at a slightly different metre.
Now, my honorable colleague adds that a neutral meridian appears to him a myth, a fancy, a piece of poetry, so long as we have not exactly settled the method of determining it. I shall disregard the expressions which my honorable colleague has thus introduced into the discussion, because this discussion should be serious. It is plain that Prof. Abbe did not thoroughly apprehend the explanations which I gave of the proper methods of fixing the initial meridian, and of the conditions which make a meridian neutral; but I return to them, since I am invited to do so. Our meridian will be neutral if, in place of taking one of those which are fixed by the existing great observatories, to which, consequently, the name of a nation is attached, and which by long usage is identified with that nation, we choose a meridian based only upon geographical considerations, and upon the uses for which we propose to adopt it.
Do you want a striking example of what differentiates a neutral meridian from a national meridian? In order to avoid the confusion which existed in geography at the beginning of the seventeenth century, on account of the multiplicity of initial meridians then in use, a congress of learned men, assembled in Paris at the instance of Richelieu to select a new common meridian, fixed its choice on the most eastern point of the Island of Ferro. This was a purely geographical meridian, being attached to no capital, to no national observatory, and consequently neutral, or, if you please, purely geographical. Later, Le père Feuillet, sent in 1724 by the Academy of Sciences to determine the exact longitude of the initial point, having given the figure 19° 55' 3" west of Paris, the geographer, Delisle, for the sake of simplicity, adopted the round number 20°; and, as I stated a little while ago, this alteration completely changed the character of this prime meridian. It ceased to be neutral, and became merely the meridian of Paris disguised, as has been truly said, and the English, notably, never adopted it. Here is the difference, gentlemen, between a neutral meridian and a national meridian.
And, parenthetically, you see, gentlemen, how dangerous it is to awaken national susceptibilities on a subject of a purely scientific nature. Now allow me to add that, if in 1633 it was possible to find a neutral meridian, a purely geographical meridian, an independent meridian, it may easily be done in 1884 if we wish to do so; and that a point chosen on purely geographical considerations, either in Behring's Strait or in the Azores, could be much better determined now than was possible to Father Feuillet in 1724, and could take the position which the meridian of Ferro would not have lost had it not been confounded with the meridian of Paris.
Professor J. C. Adams, Delegate of Great Britain, stated that he merely desired to refer to one subject touched on by the Delegate of France, Mr. Janssen, whose opinion he thought could hardly be supported, and that was that the question of longitude was purely one of geography. He desired to controvert that, and to hold that the question of longitude was purely one of astronomical observation. The difference of longitude between two places could not be determined by geodetic observations, because to do this you must take hypothesis as to the figure of the earth, and the figure of the earth is not a simple figure. You may take as hypothesis that the figure of the earth is spheroidal, and that the ratio of the axes is exactly defined. Now, in the first place, we are not agreed as to the exact ratio of the axes, nor are we agreed as to the exact figure of the earth. If an attempt is made to measure the difference of longitude between two points on the earth's surface, especially when they are a considerable distance from each other, it is necessary to depend upon astronomical observations. In attempting to deduce the difference of longitude from geodetic measures, you must assume that the true figure and dimensions of the earth are known, which is far from being the case. The theory that the prime meridian is a matter purely of a geographical nature is liable to the fatal objection that the determination of the difference of longitude between one place and the other is really the determination of the difference of time of the passage of a star across the meridian of the two places concerned. That is very definite. You observe the transit of the star at one place, and you observe the transit of the star at the other place, and by means of telegraphic communications you are able to determine their difference of longitude independent of the figure of the earth. He said, in conclusion, that he thought the honorable Delegate of France was mistaken upon the main point which he had just referred to, if, indeed, he had rightly understood him.
M. Janssen, Delegate of France, replied as follows:
I think that M. Adams entirely misunderstands me. I agree with him absolutely in thinking that longitudes cannot be determined, especially of places far apart, except by astronomical methods. Geodesy can only furnish it for short distances; in such cases, it is true, it supplies it with a degree of accuracy which meridianal observations cannot attain. So, if the question be to determine rigorously the difference of longitude in time between two places on the earth at considerable distances apart, it becomes one of astronomy, because here it is astronomy which gives the quickest and most accurate solution. For these reasons if, for instance, we should wish to connect a given observatory with a point situated on the other side of the ocean which had been chosen as the starting point of longitudes, it would become a question of astronomy. Astronomy here is an admirable instrument for the solution, but it should only be the instrument.