If, then, we are of one mind as to the desirability of a single prime meridian, and if we are fully empowered to make the selection, which may be taken as another way of saying that we are directed by our respective Governments to make the selection, we may proceed directly to the performance of this duty.

In the choice of a prime meridian, there is no physical feature of our earth which commends itself above others as the best starting point; nor does the form of the earth itself present any peculiarity which might be used as an initial point.  If the refinements of geodesy should finally lead to the conclusion that the figure of the earth is an ellipsoid with three axes, yet the question of the direction of either of the equatorial axes must remain to such a degree uncertain that the extremity of the axis could not be assumed as the point of departure for counting longitude.  Indeed, as an initial meridian must above all things be fixed in position, it would not answer to make its position depend upon any physical constant which is itself in the slightest degree uncertain; for in these days, when refinements in physical measurements are constantly leading to more and more accurate results, each advance in accuracy would necessitate an annoying change in the initial meridian, or, what would more probably result, the retention of the first chosen meridian, which would thus lose its dependence upon the original definition, and become as arbitrary as if taken by chance in the first instance.

We may then say that, from a purely scientific point of view, any meridian may be taken as the prime meridian.  But from the standpoint of convenience and economy there is undoubtedly much room for a choice.

Considering this question of convenience in connection with the necessary condition of fixity already referred to, the prime meridian should pass through some well-established national observatory.

In making the choice of a prime meridian which is to serve for a great period of time, it is important to so fix and define it that the natural changes of time may not render it in the least degree uncertain.  To this end, the nation within whose borders the chosen point may fall should engage to establish it in the most enduring manner, and protect it against all possible causes of change or destruction.

When taken in connection with other requirements, to be mentioned hereafter, this character of permanence will be best secured by making the adopted meridian pass through an observatory which is under the control of the Government.

Such observatory should be in telegraphic communication with the whole world, in order that the differences of longitude from the prime meridian may be determined for any point.  These conditions of convenience are so important that they may fairly be considered imperative.  To fulfil them one of the national meridians now in use should be selected.  To select any other than one of these meridians, or a meridian directly dependent upon one of them, and defined simply by its angular distance from one of these national meridians, would be to introduce endless confusion into all charts and maps now in use.