of very small spots, like that of April 30, 1908, are surrounded by a great cyclonic structure in the hydrogen flocculi, extending over a distance equal to about one third of the Sun's diameter, while it is frequently true that large spots, with strong magnetic fields, seem to influence the form of the flocculi over a very much smaller area. Thus it can hardly be said that such evidence is favorable to the electro-magnetic explanation, particularly when it is remembered that beautiful cases of apparent lines of force or vortex structure, covering great areas, are frequently shown on Ha photographs in regions where no spot is present.

The questions raised in these notes will be discussed more fully in a paper containing the quantitative results of the present investigation, which will soon be published. A single suggestion may, however, be added here. If the apparent lines of force uniting two spots of opposite polarity are of hydrodynamical origin, they suggest that one spot should be regarded as a source and the other as a sink. AS EVERSHED'S published results all indicate an inward flow at the H, level, the existing data seem to be opposed in this case to the hydrodynamical explanation.

A REVIEW OF THE RECENT OBSERVATIONS OF

MARS.

By R. G. AITKEN.

It is my purpose this evening to give you a short account of the recent observations of Mars, and of the general conclusions that I think may fairly be drawn from these observations. As a man's opinions are necessarily influenced in a greater or less degree by his experience and training, it may be well to premise that I speak from the point of view, not of the expert areographer, but of the interested student, who has familiarized himself with the literature of the subject and who has also had many opportunities during the past sixteen years to study the planet directly, under favorable observing condi

1 This is an abstract of an address given before the Society at its annual meeting on March 26, 1910. Lantern slides of drawings and photographs of Mars made during the last three opposition periods were exhibited to illustrate the address.

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MERIDIES

180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 0

Cydonia

tions, with refracting telescopes varying in aperture from 31⁄2 inches to 36 inches.

We may say, then, that in recent years observations of Mars have had for their main object the settlement of two questions

(1) What is the nature of the surface detail, and, particularly, of that portion known as the "canals"? (2) Is it possible by direct observation to establish indisputably the fact that water vapor exists in the Martian atmosphere? In connection with the former a practical question of considerable interest has been raised, namely, the size of telescope best adapted to the study of planetary detail.

What light have the observations during the recent opposition of the planet thrown upon these questions?

No complete account of Mr. LoWELL'S work during the past year has as yet been published, but from some short bulletins. and notes from his pen it is clear that his observations have only confirmed him in the views that he has previously expressed. For example, he has recently announced the discovery of two canals-new not only in the sense that they had not previously been seen by terrestrial observers, but also new, in his opinion, to Mars itself. Speaking of these canals, he says: "In form they are like all the other canals-narrow, regular lines of even width throughout, running with geometric precision from definite points to another point where an oasis is located. This oasis resembles all the other oases-a small, round, dark spot. They partake, therefore, of all the peculiar features of the canal system-features which I have elsewhere shown make it impossible of natural creation, that is, of being the result of any purely physical forces of which we have cognizance. On the other hand, the system exactly resembles what life there would evolve under the conditions we know to exist." 1

Mr. LOWELL thus gives a clear statement of one answer to our first question. In his view, the canals are the visible evidence of a vast irrigation system developed by Martian engineers to husband and distribute economically the scanty supply of water that exists upon the planet.

1 Nature, 82, 489, 1910.

The great majority of observers during the past opposition, however, take direct issue with Mr. LowELL on this point; for almost without exception their testimony is that they have been unable to detect any evidence of the existence of this geometrical network of canals. Surface detail in abundance they have seen and drawn in their sketches, including many canals. But the latter are, in general, not of uniform width and shading; they are not perfectly straight; they do not follow great circle arcs. In general, too, they are not so narrow as Mr. LowELL's canals. In a word, they have a less artificial and a more natural appearance. Thus, the well-known English observer, Mr. A. STANLEY WILLIAMS, uses the word "irregularity" to characterize the dominant impression received by him in his study of the planet's surface. There were plenty of so-called canals, "but not one of them could be described as a geometrical, narrow, straight line of uniform width. All were obviously more or less irregular or complex." M. COMAS SOLA and M. ANTONIADI, who, like Mr. WILLIAMS, are observers of recognized ability and who have, like him, studied Mars for years, are even more emphatic in their statements. Indeed, they do not hesitate to say that the geometrical canal system is a pure illusion.

M. R. JONCKHEERE, on the other hand, enthusiastically supports Mr. LowELL'S observations and, in fact, surpasses them. For, with a 14-inch telescope, he sees all of the older canals, verifies every one of the four hundred discovered at Flagstaff, and adds twenty-three new ones!

I have mentioned only a few observers and only a few typical statements of results. The time limits set me do not permit me to go into great detail. But I think it will be clear to you from what I have said that our first question is not yet conclusively answered.

It should be noted that Mr. WILLIAMS's telescope is a reflector with a 61⁄2-inch mirror; that M. COMAS SOLA employed a refractor of 15 inches aperture, while M. ANTON LADI enjoyed the privilege of using the 331⁄2-inch Meudon refractor, the largest one in Europe. Mr. LOWELL, as is well known, uses a 24-inch refractor, which, if I am not mistaken, he sometimes, or frequently, stops down to a smaller aperture. These details have a significant bearing upon the practical question