the liberal co-operation of the society on whose premises one portion of them was to be carried on, and of the dignitaries of the cathedral, who afforded the most admirable station for the other part of the operations. The local advantages afforded for such inquiries at York are considerable. The great valley, or rather plain, which takes a sweeping course through the centre of Yorkshire, from the mouth of the Tees to the estuary of the Humber, and varies in breadth from fifteen to twentyfive miles, presents not a single elevation of any kind, approaching to more than half the height of the central tower of York Minster, which is 200 feet from the ground. Here one of the rain-gauges was mounted on a pole, so as to rise some feet above the battlements of the tower. It was thus in a situation to give really a fair sample of the condition of the free atmosphere. The local circumstances, Mr. Phillips observes, "give an importance to the moderate height of York Minster, which is denied to many loftier buildings in England. From its summit, the course of a passing storm may be well traced from even the distant hills of Richmond; and the deflections occasioned by the attraction of the sides of the vale, the rushing of the air, the sudden fall of temperature, and many other curious phenomena accompanying the precipitation of rain, may be well observed. It is, probably, to the peculiarity of its geographical situation, that we are to attribute the remarkable general regularity of the curves of mean temperature at York." The other stations were at the Museum of the Yorkshire Philosophical Society; this is situated just out of the town to the West. Its roof is the highest point in the immediate neighbourhood; it stands apart in the society's grounds. A gauge was fixed on the roof, about thirty feet from the ground. In the grounds, at some distance from the building, in the centre of an open lawn, was placed the third gauge, sunk in the ground, having its edge nearly level with the grass. These gauges were of a good yet simple construction; and all the arrangements made with a view to ensuring the accuracy and regularity of the observations were admirable. We speak with confidence, from having ourselves examined the whole, with the advantage of the able explanations of Mr. Phillips, in 1834. To the unabated zeal of that gentleman, science owes much in all its departments; but as our object here is not the praise of an individual, but the exposition of his results, we will only state, that with the most unremitting diligence, aided only occasionally by some friends, especially Mr. W. Gray, jun., of York, he carried on constant observations at the three stations, obtaining carefully, at certain intervals, the amount of rain which had been collected respectively, in the three gauges. The results for an entire year are fully stated in a Report communicated to the British Association, at the meeting of 1833. These observations establish and confirm in the most undeniable manner, the singular and anomalous result already alluded to, that the quantity of rain increases, by some means, during its fall, as it approaches the ground; being greatest at the surface of the ground, less at a small height, and least at a greater height. Mr. Phillips enters into a variety of considerations with the view of accounting for this phenomenon. He commences by endeavouring to deduce some numerical ́relation, or law, among the observed numbers: these inferences were, indeed, confessedly, but rough approximations in the first instance; they were, however, fully such as authorized the belief of their pointing to some real law of nature. The diminution in the formation of rain in the upper parts of the atmosphere, appeared to be greatest in the cold, and least in the warm months. Its relation to the degree of dryness of the air, or the quantity of invisible vapour suspended in it, was a point requiring particular examination: and the degree of diminution was found to hold a very close and simple relation to the dryness. The results thus obtained, enabled the author to offer an explanation of the phenomenon, possessing a high degree of probability: namely, "that the whole difference in the quantity of rain at different heights above the surface of the neighbouring ground, is caused by the continual augmentation of each drop of rain, from the commencement to the end of its descent, as it traverses successively the humid strata of air at a temperature so much lower than that of the surrounding medium, as to cause the deposition of moisture on its surface." It is not, then, an increase in the number of drops, formed at lower points in the air, but each single drop increases in size, like a snow-ball, acquiring fresh depositions on its surface, from the moisture of the region through which it passes. The drops descend from a colder region, and bring their temperature with them. We recognise this in the familiar observation, that a shower cools the air. The increase takes place not at a uniform, but at an accelerated rate, in approaching the ground; this is a general rule, though not as yet reduced to an accurate law; but it is fully accounted for by the above hypothesis of the mode of increase. The numerical results, however, yet only furnished general approximations. Desirous, therefore, of obtaining a still increasing accuracy in these important data, Mr. Phillips went through another entire year's set of observations: the account of which was, like the former, communicated to the British Association. This report, presented at the Edinburgh meeting, gave a more decided confirmation of the increase of the quantity of rain as it approaches the ground: the quantities at the three stations being, (roughly,) in the ratio of the numbers, fourteen, nineteen, and twenty-five; the rate of increase being less in warmer weather. The results were exhibited in tables, and at least, a general accordance with a mathematical law was observable throughout. The subject excited much interest at that meeting, and considerable discussion took place; in the course of which, Mr. L. Howard, (well known for his researches on the meteorology of London, &c.,) stated, that fully admitting the value of Professor Phillips's observations, he differed from him as to the theory. His own opinion was, that the actual number of drops increases near the surface, or that the actual deposition from the atmosphere, continues to originate new rain at all heights, or at least, at different heights, according to the various conditions of temperature, moisture, &c., but principally, in relation to the electric condition of the mass of air or vapour; and though he does not deny that each drop may acquire an accession, yet he thinks it so small as to be quite insensible. We confess for our own Various arguments arose on this objection. part, the circumstance which appears decisive on the question, is the regularity with which the effect follows in numerical amount all the variations of those causes which should produce it on Professor Phillips's theory; whereas, we see no indication of its following any relation to electric action. That regularity of sequence and constant association in all the variations of one general fact with another, is, we believe, to say the least, the most undeniable indication of a real connexion of the two as physical cause and effect; the precision of these numerical laws, has since been still more powerfully confirmed. At the Dublin meeting of the British Association, Professor Phillips presented his report of a third series of twelve months' observations by the same method, and conducted at the same positions. The preceding sets of observations having determined the general fact of the increase in the quantity of rain as it approaches the ground, and the dependence of the amount of increase on the mean temperature of the season and humidity of the air, the object of the present inquiry was to trace more closely the precise law, or rate of increase, and to compare the indications of experiment with the mathematical formula. Several additional precautions were now employed to guard against various sources of fallacy, which might be imagined likely to affect the results. The calculations founded on these observations, combined with those of preceding years, led to the following general results: 1. The continual augmentation in size, of every rain-drop as it descends towards the earth through the strata of the atmosphere loaded with vapour. 2. That this augmentation increases faster than in the simple increase proportion of the distance from the ground. 3. That the rate of this increase varies at different seasons, and in a certain determinate relation to the mean temperature of the season. The mathematical laws of these facts are combined in one simple algebraical formula, which is found to represent very accurately the numbers actually observed. Thus Professor Phillips has suggested to us, a sort of philosophical history of a rain-drop; from its birth in the upper regions to its burial in the earth. And it is an instructive history, as it reveals to us the condition of the atmosphere through which the drop has taken its course, under the combined influence of the temperature, the quantity of vapour suspended in the air, the varying currents of the atmosphere, and other circumstances which contribute to the formation of rain. These observations, however, it must be remarked, apply only to one locality: certainly a very favourable one for such observations. It becomes an extremely interesting inquiry to those who value the promotion of a knowledge of the constitution of the atmosphere, to have similar observations repeated at various other stations. We believe the British Association have organised some system by which such observations may be set on foot in different parts of the kingdom, But it is manifestly, a class of observations in which persons without any profound scientific attainments, with only a little perseverance and accuracy, may do much for the advancement of experimental knowledge. For full details, we refer those interested in the subject, to the several volumes of the Reports of the British Association. STEAM AND GAS. AMONG the physical agents which, by stimulating our curiosity in the examination of their qualities and habits, are wisely appointed to minister to our necessities and our enjoyments, there are none, perhaps, which have exercised the ingenuity or tested the patience of man with happier results than water and coal. STEAM and GAS furnish decisive and beautiful illustrations of what untiring perseverance is capable of accomplishing. They exhibit some of the elements of nature brought into a state of combination that fits them, if left uncontrolled, to spread terror and death; but when under proper management, we behold them in such a state of subjection, that it may literally be said "a little child may lead them." So intimately associated are steam and gas with our own age and country, their properties and capabilities occupy so large a portion of public attention, in almost every part of the civilized world, that we think we cannot introduce more interesting subjects for contemplation, than are suggested by some of the modes of employing the one and of preparing the other. All that we intend at present is a few general remarks. Let these be viewed as introductory to more elaborate accounts. The active properties exhibited by steam, and by which it is so eminently adapted for a motive power in machinery, are due entirely to heat. It is not worth while to attempt a solution of the question, What is heat? because we believe the endeavour would be only a waste of time. Heat may be an elementary substance, existing, in some cases, independently of matter, or it may be merely a condition of matter, and inseparable from it; yet influencing its forms, and producing in it changes, with a degree of certainty, that is equalled only by its extraordinary energies. From what we know of heat, by its effects, we may affirm that it is a highly-refined, an all-pervading, and an irresistible agent. It is known to us only as it is combined with the diversified forms of matter, and we know nothing of matter unassociated with heat. With this ignorance respecting the nature of heat, it seems we must at present be contented. Steam is water in a very minutely divided state; by which division it is capable of containing, and of carrying along with it, under particular circumstances, to any required distance, a greater quantity of heat than when in its ordinary state as a liquid. But whilst this capacity for heat, as manifested by water in a state of vapour, is one cause of its great utility, it possesses another peculiarity not less important, namely, the facility with which a certain portion of the heat may be separated from the water with which it had been temporarily combined; the steam, by a very simple expedient, instantaneously assuming the liquid form, and the heat as quickly disappearing, and taking up its abode in some other material. Heat and water, then, are the primary sources of motion in those wonderful combinations of machinery denominated the steam-engine. At no very distant period, it will be our business to show how these powerful agents co-operate in producing those results which, whilst they excite our admiration, should also awaken our gratitude. Turn we now, for a few moments, to gas, which, like steam, owes its existence to heat. In a general sense, gas implies those substances which retain the aëriform state under ordinary circumstances of temperature and pressure. We shall limit our observations to coal-gas; that being the material to which we alluded in a former part of this paper, and which is now so extensively employed as a medium of artificial light in this country, in many of the principal towns on the Continent, and in the United States of America. We mentioned above, as a valuable property of steam, that a part of the heat it contained could be so easily separated from it; entering into some other material, and leaving the water as it found it, that is, in the liquid state. A property the very reverse of this is possessed by coal-gas. The inflammable and luminous elements which enter into combustion with heat, in the formation of this curious substance, retain so firm a grasp of each other, if we may be allowed the expression, that neither cold nor pressure of any ordinary kind will separate them. Hence it is that gas may be stored and kept ready for use, and transmitted with certainty, both as respects time and quantity, to any distance from the place where it is produced. To those who have never thought much upon this subject, it may appear strange that a part of the heat, and consequently, of the light, emanating from gas, burning several miles distant from the manufactory, is the very same heat and light which, a few hours before, had been produced by the combustion of coal or coke. Such, however, is the fact. The heat arising from the ignited fuel passing through the retort, and combining with certain elements in the coal, constitutes gas. That gas, whether stored for use, or immediately passed into the mains, finds its way, in a little time, to the burner,—it may be in a street-lamp, a shop, or a drawing-room; but wherever it makes its appearance in a state of ignition, it there yields up a part of the heat it received at the manufactory; its elements are transformed, scattered hither and thither, and are thus prepared for new combinations in the economy of the universe. LEVELLING. SIMPLE AND EFFECTUAL MODE OF DETECTING ERRORS IN LEVELLING OBSERVATIONS. IN the best modern levelling-staves, as for instance, those for which a Telford medal was awarded to Mr. Gravatt, C.E., last year, by the Institution of Civil Engineers, the observation is at once read off by the surveyor, instead of being reported to him by the assistant; a saving of time, and a diminution of the sources of error, are the consequence. But still, if a surveyor, on the conclusion of his field-work, suspects an error, he has no other means of discovering the place of the error, or removing the suspicion, but recommencing the survey and repeating part, probably the whole, of his observations. A very valuable suggestion has been made by Mr. Henry E. Scott, which, if adopted by a surveyor, would, almost to a certainty, enable him, by merely referring to his field-book, and without repetition of a single observation, to detect the place of the error, and |