Each phenomenon is highly suggestive considered alone, but each acquires still greater significance from its association with the other; for here in the oases we have an end and object for the existence of canals, and the most natural one in the world, namely, that the canals are constructed for the express purpose of fertilizing the oases. Thus the mysterious rendezvousing of the canals at these special points is at once explicable. The canals rendezvous so entirely in defiance of the doctrine of chances because they were constructed to that end. They are not purely natural developments, but cases of assisted nature, just as they look to be at first sight. This, at least, is the only explanation that fully accounts for the facts. Of course all such evidence of design may be purely fortuitous, with about as much probability, as it has happily been put, as that a chance collection of numbers should take the form of the multiplication table.

In addition to this general dovetailing of detail to one conclusion is to be noticed the strangely economic character of both the canals and the oases in the matter of form. That the lines should follow arcs of great circles, whatever their direction, is as unnatural from a natural standpoint as it would be natural from an artificial one; for the arc of a great circle is the shortest distance from one point upon the surface of a sphere to another. It would, therefore, if topographically possible, be the course to take to conduct water, with the least expenditure of time or trouble, from the one to the other.

The circular shape of the oases is as directly economic as is the straightness of the canals; for the circle is the figure which incloses the maximum area for the minimum average distance from its centre to any point situated within it. In consequence, if a certain amount of country were to be irrigated, intelligence would suggest the circular form in preference to all others, in order thus to cover the greatest space with the least labor.

Following is the list of the oases so far discovered :--

Acherusia Palus
Aganippe Fons
Alcyonia
Ammonium
Aponi Fons
Aquae Apollinares
Aquae Calidae
Arachoti Fons
Arduenna
Arethusa Fons
Arsia Silva
Arsine
Augila
Bandusiae Fons
Biblis Fons
Castalia Fons
Ceraunius
Clepsydra Fons
Cyane Fons
Ferentinae Lucus
Fons Juventae
Gallinaria Silva
Hereynia Silva
Hibe
Hippocrene Fons
Hipponitis Palus
Hypelaeus
Labeatis Lacus
Lacus Ismenius
Lacus Lunae
Lacus Phoenicis
Lerne
Lucrinus Lacus
Lucus Angitiae
Lucus Feronia
Lucus Maricae
Maeisia Silva
Mapharitis
Mariotis
Meroe
Messeis Fons
Nitriae
Nodus Gordii
Pallas Lacus
Propontis
Serapium
Sirbonis Lacus
Solis Fons
Solis Lacus
Tithonius Lacus
Trinythios
Trivium Charontis
Utopia

II. Double Canals

To see them, however, all that is needed is a sufficiently steady air, a sufficiently attentive observer, and the suitable season of the Martian year. When these conditions are observed, the sight may be seen without difficulty, and is every way as strange as Schiaparelli, who first saw it, has described it.

So far as the observer is concerned, what occurs is this: Upon apart of the disk where up to that time a single canal has been visible, of a sudden, some night, in place of the single canals he perceives twin canals,--as like, indeed, as twins, if not more so, similar both in character and in inclination, running side by side the whole length of the original canal, usually for upwards of a thousand miles, of the same size throughout, and absolutely parallel to each other. The pair may best be likened to the twin rails of a railroad track. The regularity of the thing is startling.

In good air the phenomenon is quite unmistakable. The two lines are as distinct and as distinctly parallel as possible. No draughtsman could draw them better. They are thoroughly Martian in their mathematical precision. At the very first glance, they convey, like all the other details of the canal system, the appearance of artificiality. It may be well to state this here definitely, for the benefit of such as, without having seen the canals, indulge in criticism about them. No one who has seen the canals well--and the well is all