exactly as possible. On or about December 6,* the Earth crosses the plane of the Sun's equator (passing southwards), and then the Sun is presented as at 1, fig. 46. Three months later, the Earth reaches her greatest distance south of the solar equator, so that on or about March 6 the Sun is presented as at II. On about June 5 the Earth again crosses the plane of the solar equator, this time passing northwards, and the Sun is presented as at III. Lastly, on about September 5, the Earth reaches her greatest distance north of the solar equator, and the Sun is presented as

at IV.

The observations of Schwabe and Carrington have been continued, under improved conditions, by De La Rue, Stewart, and Loewy. The powers of photography, under the able superintendence of Mr. De La Rue, have been applied to secure records of the aspect of the solar disc on every clear day. But independently of the valuable series of records thus obtained, the three physicists above named have undertaken a careful scrutiny, not only of the solar photographs taken at Cranford and afterwards at Kew, but of the observations made by former students of the solar surface. Accumulating a vast mass of records, they have applied processes of statistical research to educe any information

The date for any year can always be determined from the almanac. It is only necessary to note when the Sun's longitude is 180° + the longitude of node of Sun's equator (say 180° + 74°, or 254°). In like manner, the Earth is again in the plane of the solar equator when the Sun's longitude is about 74°. The solar longitude is given for each day in Hannay's Almanac, in the last column of the first page for each

month.

respecting the Sun, which, though in reality contained in observations already made, may not lie at or even near the surface.*

In the three papers by De La Rue, Stewart, and Loewy, entitled Researches on Solar Physics,' we find an extension and elaboration of the modes of research employed by Wilson, Schwabe, and Wolf. Where Wilson inquired into the behaviour of individual spots, our three allies discuss the peculiarities presented by hundreds of spots. Where Schwabe discussed the number of new groups of spots, they consider the area of the spotted portion of the Sun's surface. And, lastly, where Wolf examined the evidence which the numerical statistics respecting spots afford in favour of the theory that the planets exert an influence on the solar envelopes, De La Rue and his colleagues inquire into the behaviour of individual spots as they approach or cross the region towards which the several planets lie, they examine the general distribution of spots as respects proximity to the equator under certain circumstances of planetary position, and by discovering other like peculiarities they obtain evidence altogether distinct in character from that adduced by Professor Wolf.

Taking first the question whether the umbræ of spots are below the level of the photosphere, the inquirers examine 605 observed cases of spots having measurable

* It is a promising sign of progress when students of science are thus willing to discuss the labours of others as well as their own, undeterred by the fear of being called mere theorists.

penumbræ, and they find that while in seventy-five instances the penumbra is equal on both sides (referring to Dr. Wilson's mode of dealing with the question), in 456 instances the penumbra was widest on the side nearest the limb, while in seventy-four the penumbra was narrowest on that side. Hence the percentage of favourable instances is 75-37; of unfavourable cases, 12-23; and of neutral cases, 12:40. This seems to place the existence of a real depression beyond question; while at the same time it demonstrates the truth of what Carrington has said respecting Wilson's observations,—that there is more variety in the appearances than Wilson confesses to, and there are marked departures from his description of form, which is rather one specific type out of several which might be adduced, and will be familiar to every one when photography has furnished us with forms on which all, whether observers or not, may rely.' I would invite the special attention of the reader at this point to Plate I., where Mr. Browning has delineated a case in which two spots close by each other exhibit altogether different characteristics, one agreeing with Dr. Wilson's description, the other presenting an opposite peculiarity. I was much struck with the great variety observable in this respect, when I was drawing the picture which

In the Researches the neutral instances are not taken into account, and thus the percentage of favourable cases becomes 86-04, and that of unfavourable cases 13-96. But the rejection of neutral cases is not in accordance with the accepted rules for dealing with such matters. I can discover no reason for making an exception in this particular

case.

illustrates this chapter (Plate II.), though the low power I employed did not permit me to see the minuter details of the spots.*

Next, investigating the relative position of spots and their accompanying faculæ, our inquirers find that out of 1,137 spots, 584 have their faculæ either wholly or mostly on the left-that is, behind them, as respects the motion of solar rotation, 508 have the faculæ nearly equally on both sides, while only forty-five have their faculæ mostly on the right. The most natural explanation of this would be,' they say, that the faculæ of a spot have been uplifted from the very area occupied by the spot, and have fallen behind to the left from being thrown up into a region of greater velocity of rotation.'

Thirdly, they attack the following question: Is a spot, including both umbra and penumbra, a phenomenon which takes place beneath the level of the Sun's photosphere or above it?' They note in evidence on this matter, that there are many instances in which

The telescope I employed was a very small one, about 24 inches in aperture. I used an ordinary erecting eye-piece, having a power of about 26. Thus seen, the Sun appeared in the middle of a large field, and I could scarcely have believed that I should have been able to recognise the features I had seen with larger telescopes and higher powers. I had never before examined the Sun with so low a power (for four years before the day on which the design for Plate II. was drawn I had had few opportunities for observation), and it was with a sense of considerable pleasure that I found the familiar features coming clearly into view as I scrutinised the tiny image more and more searchingly. I found myself able to comprehend better than ever before how Galileo with his small telescope and low power (30) had been able to detect so many features of the Sun's surface.

'a bridge of luminous matter of the same apparent luminosity as the surrounding photosphere, and unaccompanied by any penumbra, appears to cross over the umbra or centre of a spot.' Detached portions of luminous matter are also seen at times to move across a spot without producing any permanent alteration. 'On these accounts,' say the inquirers,' we are disposed to think that a spot, including both umbra and penumbra, is a phenomenon which takes place beneath the level of the brighter part of the Sun's photosphere.' Summing up the results of this portion of their researches, they express their belief that,—

1. The umbra of a spot is nearer the Sun's centre than the penumbra, or, in other words, it is at a lower level.

2. Solar faculæ, and probably also the whole photosphere, consist of solid or liquid bodies of greater or less magnitude, either slowly sinking or suspended in equilibrium in a gaseous medium.

3. A spot including both umbra and penumbra is a phenomenon which takes place beneath the level of the Sun's photosphere.

As respects the sequent series of researches by which Messrs. De La Rue, Stewart, and Loewy have endeavoured to estimate the influence of the planets upon the solar spots, it is to be remarked that the evidence adduced seems as yet not wholly decisive. They believe that it has been rendered probable that Venus exerts a special influence on the solar spots, and that the conjunctions of the planets also affect