northern patch of snow varies but slightly in dimensions, the southern is of great size in the winter, and almost vanishes in

summer.

From the foregoing facts, and the deductions which may naturally be drawn from them, the reader has ample means for judging, in this individual instance at least, as to the probability of the planets being the abode of animal and vegetable life. It would be impossible, of course, to give any minute details on this point, to say that such a place is forest land, or cultivated ground, or artificial formations; for when Mars is nearest the Earth-making use of the most powerful telescope yet constructed, the observer is merely able to tell whether a space of ground which is two hundred miles long by two hundred broad, or an area of 40,000 miles, is round or square. From this circumstance, the observations of Schroeter, who saw clouds passing over the planet with a velocity from forty to sixty times that of the most violent hurricanes on the Earth, have been much doubted. But otherwise we have every evidence of an atmosphere, of snow, of changeable weather, of bright and sunny skies, of the existence of water. The seasons, though not so equable in duration as those on the Earth, are still present, with all their agreeable changes; we see the seed-time and harvest, the ripening summer and the dark winter. The isothermal lines on the Earth are reproduced on Mars, if we are to judge by the position of the snow-zones, which are not placed exactly at the poles. Nor does the excessive cold which might be surmised to take place from the planet's distance from the solar heat really appear to be so severe. Whether, from some peculiarity in the atmosphere, the latent heat of the body itself, or other causes unknown to us, the polar snows do not appear of the vast extent which might be imagined. Even those thaw away with a rapidity which seems marvellous, whilst the equatorial regions are altogether free from such visitations. Venus receives four times the heat of Mars, and twice that of the Earth; yet at the North Pole of Venus, a bright white and large spot has been perceived, which may naturally be surmised to be of the same nature as the snow-capped poles of the Earth and Mars; and we might from this conclude that no great difference exists in those three planets at least, whatever may be the case in the other two groups of planets,-i.e., the seventysix asteroids, or the huge exterior planets of small density, quick rotation, and accompanied by numerous moons and a ring.

The diameter of Mars is about twice that of the Moon, and more than one-half of that of the Earth. Its surface is about four times greater than that of the former, and is one quarter that of the latter. Bulk for bulk, Mars is seven times larger than the Moon, and the Earth is seven times larger than Mars.

Weight for weight, the Earth is more than seven times heavier than Mars. It would take upwards of two and a half millions of bodies like Mars to counterpoise the weight of the Sun. We thus see that Mars, with its diameter of 4,100 miles, holds a geometrical mean between the Moon and the Earth. The attraction, fall of bodies, and length of pendulum, are about onehalf of what those are on the Earth. Unlike the latter body, it has no satellite, although, if this latter were thirty miles in diameter, it could not pass unnoticed.

Maedler has calculated the duration of the seasons in Mars, which are as follows::

From Spring to Summer (Spring in North, Summer in South), 191 days.

Summer to Autumn (Summer in North, Winter in South), 181

Autumn to Winter (Harvest in North, Spring in South), 149

Winter to Spring (Winter in North, Summer in South), 147

22

It will thus be seen that there are 372 days of spring and summer in the northern, and only 296 days in the southern hemisphere. The winter in the north only lasts 147 days; in the south 181 days. The heat and light in the northern summer is as 20 to 29 to the south. The consequence of this will be, that there is a long temperate summer, and a short mild winter; whilst in the southern, there will be a short hot summer, and long and severe winter.

The sixth figure gives a map of one of the hemispheres of Mars, as drawn by Maedler, and shows what may be done by means of a small telescope. The seventh and eighth figures represent the opposite hemispheres of the planet as drawn by the writer on December 10, 9h. 20m., and November 22, 10h. P.M., 1862. The spots in the seventh figure would appear to be the best defined of the planet, and bear a striking resemblance to those seen in 1719 by Maraldi, on August 19 and 20, and September 25 and 26, as also to that seen by Sir W. Herschel on October 10, 1783, at 6h. 55m. P.M.

MISCELLANEA.

THE BRITISH ASSOCIATION AT CAMBRIDGE.

PART I.

BY PROFESSOR D. T. ANSTED, M.A., F.R.S.

THE

HE late meeting of the British Association, held during the first week of October in the University of Cambridge, has been one of those that may be regarded as successful, both in reference to the scientific men present and the communications made. It was not large, numbering only about 1,200 members in all; but the absentees, though including some wellknown and familiar names, were chiefly the amateurs of science, associates, ladies, and those who join only for the current meeting; not working members, to whose labours the meetings are chiefly indebted for their important practical results. The sections were fairly attended, without being crowded, except on some few special occasions. The evening meetings were also well attended; and although the monetary returns will hardly be very brilliant, the reminiscences of Manchester and the prospects of Newcastle will console the treasurer for the comparative emptiness of the purse on this occasion. The Association meets one year for itself and another for the place it visits. At Cambridge, on the occasion of this, its third visit, there was not much enthusiasm, but there was a very pleasant assemblage of numbers of old members, who had been long without seeing one another, but who were not less warm in their greeting than if they had been annual attendants and had kept up acquaintance by frequent visits to the annual reunion.

An absence of excitement and "sensation " certainly characterized the meeting. The President (Professor Willis), in his address, rather recalled attention to the early labours of the Association, and the fruits it had borne years ago, than to the present state of science.

The evening lectures were on subjects already worn somewhat threadbare by frequent repetition at the Royal Institution, and were certainly not complimentary to the Cambridge audience. It is much to be regretted that Mr. Glaisher's interesting account of his balloon ascents did not replace one of these, and that a notice of recent researches in some interesting department was not introduced in place of the other. In spite,

however, of these mistakes, the meeting was pleasant and satisfactory, and the communications and discussions not unworthy of the occasion.

Of the different sections, that known as A-Mathematical and Physical Science offers the greatest variety of subjects, and receives a number of communications that do not properly belong to it. Some of these should be considered in E (Geography and Ethnology), and others, perhaps, in B (Chemistry). It is no doubt difficult to determine in many cases in what way to limit so very general a term as Physics. Including Astronomy and Magnetism and, perhaps, Meteorology, it is apt to absorb Physical Geography. In something of the same way, B (Chemistry) and C (Geology) occasionally overlap. D (Natural History), if strictly confined to Biology, would be tolerably independent, though not unfrequently there are links connecting it very closely with Geology by the medium of Paleontology. Physiology is regarded as a branch of Natural History, and Statistics (F), of course, finds place everywhere. Mechanics (G) is tolerably well defined. Omitting any reference to Section D, which is in other hands, I propose to recall some of the principal and more interesting communications and discussions, not so much in a systematic outline as in a general statement.

Mr. Glaisher's balloon report, already alluded to, was the most attractive paper of the meeting, and certainly included all the elements of a popular lecture. As a meteorological communication, it was given to Section A. There were several other papers of interest, connected with meteorology, climate, and other departments of Physical Geography, about which we may say a word; some being communicated to Section A, and others to Section E. It is to be regretted that a better arrangement is not made with regard to such papers. At a scientific meeting, Physical Geography should certainly receive more consideration than Descriptive Geography and Travels, to which the geographical part of E has been mainly reduced, while Climatology-too important a branch of science to be neglectedought not to be carried to general Physics, which is already too crowded with other matter more strictly belonging to it.

The balloon ascents of Mr. Glaisher are direct results of British Association work. It has long been felt, that to determine the condition of the upper part of the atmosphere, it was not sufficient to make observations on high mountains. In such cases we always carry the earth with us, and the mere existence of a mountain-chain is a serious cause of disturbance to the atmosphere. Even isolated conical peaks in detached oceanic islands are not satisfactory. On the other hand, the car of a balloon is not a very favourable station for observing; the work required to be done involves unusual accuracy and rapidity of observation, and the instruments used are very liable to injury in the descent. A large balloon, great precautions in managing it, and repeated experiments by practised observers, were indispensable; and these are not easily obtained. Moreover, the balloon is a costly instrument for experiment, and its use involves much danger to the inexperienced. The means, however, being furnished by an association grant of last year, an observer was found in Mr. Glaisher, than whom no man living is more fit for work of this kind.

It appears, also, that Mr. Coxwell has fully justified his reputation as

the first living aërial engine-driver. He is at once intelligent, instructed, and experienced,-sufficiently bold, but by no means reckless.

The number of ascents recorded is eight, and the average time in the air in each case was under two hours. The extreme height reached was above 30,000 feet; but there are no means of telling how much higher the balloon rose, as in this ascent Mr. Glaisher was, unfortunately, insensible from cold and exhaustion, during the critical time, and Mr. Coxwell was little better. The season of all the ascents was autumn, the dates ranging between the 18th August and the 8th September. The rate of ascent and descent was various, but sometimes extremely rapid, amounting to several thousand feet in a few minutes. The number of observations required to be made almost at the same moment, during the whole ascent, is enormous, but they seem to have been made with certainty, and without inconvenience, except at extreme elevations.

The conclusions arrived at, though only partial, were interesting and important; but they require confirmation and comparison with those made at another period of the year. The observations will probably be repeated in the spring of next year, and the results will be looked forward to with great interest at the Newcastle meeting.

Mr. Glaisher's account is graphic in the extreme, and the effects he saw on some occasions, when the balloon rose above a mass of clouds into the clear blue vault of heaven, are described as altogether surpassing in grandeur and beauty any cloudscapes visible from terra firma. This part of his narrative has, however, been frequently quoted in the daily newspapers and weekly journals, and need not be repeated.

Among the scientific results obtained by these balloon ascents are the following:-1. There seems no wind blowing steadily with any uniformity of direction in the upper regions of the air over our island at any height yet reached. 2. The clouds do not seem to form according to the contour of the land, but do seem to follow the tide up the great rivers. 3. The temperature not only does not decrease regularly as greater height is attained, but, in some cases, a very low temperature was attained near the earth, and was succeeded by much warmer air at a far greater elevation. 4. The aneroid barometer may be used with advantage, and may be depended on to any attained height. Mr. Glaisher states that it is available to a pressure of only five inches of mercury. 5. The humidity of the air diminishes rapidly, and at a height of five miles is extremely small. Several suggestions were made by various members in reference to aërial navigation generally, and the whole subject was recognized as of the greatest importance.

Memoirs were communicated on Climatology and Meteorological Instruments by Mr. G. J. Symons, Mr. Plant, Professor Ansted, Dr. Gladstone, Mr. Galton, Mr. Lowe, and other members. Some of these were of much interest, but we have not space to allude further to them. Mr. Lowe's paper on Ozone was especially valuable, and included the description of a new Ozone box, showing some interesting results.

The structure of the sun's surface and the volcanoes of the moon were the subject of several communications. Mr. Nasmyth pointed out some recent harvations tending to prove that the sun's nucleus is dark and dense;