the difference between the rapidity of combustion in the light and in darkness being extremely small, and sometimes in favor of the light and sometimes in favor of the dark, while the difference between them on different days sometimes amounted to 9 per cent. This fact he held to be a proo. that the former theory had been too rashly generalised from isolated facts, and he came in general to the conclusion that the observed influences upon the rate of combustion were due to the state of the atmosphere, and not to any Solar action. Following up this conclusion, and guided by a large number of well authenticated and carefully observed experiments carried on under various circumstances, the deduction drawn was that combustion was retarded by rarifiaction and accelerated by condensation. He then detailed a number of observations by which it was found that the ratio of combustion was greater than the ratio of density. One great result of all these observations and experiments was that there is an immense number of atmospheric influences, the effect of which have as yet been undiscovered. There were, however, two conclusions which he believed to be established. First, that Solar light does not seem to exercise any sensible effect upon combustion; and secondly, that variations in the density of the air do exert a striking effect in retarding or accelerating the rapidity of the process-the rate of burning augmenting with every increment of density, and vice versa.”

Prof. Olmstead of Yale College, communicated an interesting paper on

THE AURORA BOREALIS,

in which he criticised the Electric theories of this phenomenon: "The Professor commenced by a reference to a paper which he had previously written on this subject, and which was published among the contributions to the Smithsonian Institute. In this paper he had recorded a number of facts derived from a series of observations upon the very strickingly magnificent Auroras which had been witnessed during a period of about twenty years, commencing about the year 1837. The theory which he had deduced from these facts was, that contrary to the general hypothesis which ascribes the Aurora to Terrestrial sources, its origin was cosmical, the matter being derived from the planetary spaces.-His arguments in favor of this theory, in opposition to the electrical hypothesis, were based upon the immense extent of the phenomena beyond the reach of atmos

pheric excitations; secondly, from their occurring at the same hour of the night in places very far distant from each other; thirdly, from the velocity of their motions; and fourthly from the periodicity of their occurrence during a certain time, and then disappearing altogether from the heavens. With regard to their having a revolution round the sun, he thought that to be affected by the question of zodiacal light, with which he thought they had some connection; and if it should appear that the Zodiacal Light was a ring round the earth it would not affect this conclusion. He had previously stated that the long series of brillant Auroras which had been recently witnessed would soon be over and not appear again until after a period of about forty years; the regular period being calculated at sixty years. He would ask members of the Association to remark that for five or six years past the brilliancy of the Aurora had diminished, and he would ask those who could not look back to 1837 and 1840 when the maximum brightness of the Aurora was observed, not to consider the appearances now seen as comparable to those exhibitions which the older members could remember. He would ask them only to consider as the Aurora those immense banks of light which, in 1835 and 1837 used to appear in the North West, rising into columns of a scarlet or blood-red colour, with spindles moving to the South East, and arranging themselves in a magnificent crown round the zenith; while the whole heavens were suffused with crimson light. For five or six years no such exhibition had occurred. In 1840 there were 75 strikingly magnificent exhibitions of the Aurora, while for several years they had scarcely seen one. After the discovery of the analogy between electricity and lightning, it became the practice to ascribe everything to electricity. No one could doubt that electricity holds a high place among the ultimate causes of natural phenomena; he only objected to ascribing everything to that agency without even first proving its presence. This practice had damped enquiry into many phenomena, and among others, into those relating to the Aurora Borealis, and it was always deemed sufficient to say that the Aurora was an electrical phenomena. Various arguments were urged in favour of the electrical hypothesis, and upon them he would remark that the resemblances between electricity and the Aurora had been greatly overstated. Fire, the sun, a lamp, or a star have all some resemblance to the Aurora, but from his own observation he was compelled to say that the likeness was very

faint, both with regard to the shape of the light and its motions. The reasoning was this. Lightning was known to be the discharge of electric clouds, and because the Aurora was said to be like the flash of lightning, it was supposed to be discharge of electric clouds in the higher strata of the atmosphere. This rested on very small foundations; for instance, the same Aurora had been known to be visible from the extreme point of Asia to the coast of California. Electricity would not account for this. As for the shape and form of the phenomena they might be accounted for by various means as well as by electricity. From the fore. going considerations he was led to conclude that any argument founded upon the resemblance between electricity and the Aurora was inconclusive and unsatisfactory. The defenders of this hypothesis had not agreed in anything but that the Aurora was in some way or other connected with electricity, but they disagree as to the mode in which it is done. The Professor then went on to discuss the various theories that had been advanced by different writers upon the cause of the Aurora, and in commenting upon them he begged to call attention to the real question, which was this-What is the origin of the Aurora Borealis ? Is the matter which composes it derived from the earth in any way, or does it come down from the planetary spaces? If the Zodiacal Light is a ring round the earth and affords material for meteoric stones, much more fully might it be concluded that the Aurora is ferruginous, and that would help them to explain the hypothesis that the Aurora is magnetic. No doubt, electricity might present some of the appearances of the Aurora, but it was not sufficient to account for them all. The motions of the Aurora were progressive and not instantaneous, as was the case with electric flashes. Moreover the periodicity of the Aurora was not accounted for by the electric hypothesis. By another hypothesis the Aurora was ascribed to magnetism. It must be admitted that there is some connection between the two, as is shown in various ways, but these facts merely prove that it has magnetic qualities-they prove nothing as to its origin. The material of which it is composed and its extent, are not accounted for by any of these hypotheses, while they are satisfactorily accounted for by assigning it to a cosmical origin.”

The great tides of certain bays and Estuaries are of much interest to the geologist, and from a paper contributed by Prof. Bache

it

ON THE HEIGHT OF TIDES ON THE ATLANTIC COAST,

appears that the causes producing the seunusual tides are much

more extensively distributed than hitherto supposed:-"It was well known that when the tide flowed into any bay whose mouth was favorably placed for the reception of the tide wave flowing in, the height of the tide increased as it advanced towards the head of the bay. Extended observations went to show that the same phenomenon was observable in the greater divisions of the coast. He divided the Atlantic coast into three great parts, which he called the great southern, great middle and great eastern bays. The first extended from Cape Florida to Cape Hatteras, the second from Cape Hatteras to Cape Cod, the third thence to Cape Sable and perchance to Cape Race. His own observations extended as far north as Cape Ann, and he had been assisted in making up the results by Mr. Portalis. The tidal observations for New Brunswick and Nova Scotia (including Cape Breton), and part of Newfoundland, were obtained from Captain Shortland and Admiral Bayfield of the Royal Navy, whom he desired thus publicly to thank for their kindness. He should make no farther use of the information they had communicated to him than as helping out the illustration of his theory of the rest of the coast of North America, leaving them to bring before the public and reap the honor of their own investigations. Pursuing his subject, he showed that at the southern headland of the southern bay, Cape Florida, the mean tide was 1-10th foot; at Cape Hatteras, the northern headland 2 feet; while at Savannah, at the bottom of the bay, it rose to 6 feet, and it was found that the tidal lines between these points corresponded with the lines of the coast. At Cape Hatteras, again, and Cape Cod on Nantucket, the tides were the same, (2), while at New York, the bottom of this bay, they rose to 7. At Nantucket the transition from the regime of the middle to the eastern bay was sudden, and they had within a few miles five co-tidal lines touching the coast, which elsewhere were widely apart. From Cape Cod to Cape Ann, at the bottom of the great eastern bay, there was a rise of from 2 to 8 or 9, diminishing again at Cape Sable to 6, but he had reason to believe that this bay really extended to Cape Race. He next proceeded to notice the several bays and inlets along the coast, which generally showed the same characteristics in a more marked manner. In the Bay of Fundy, for instance, the height of the tides increased from Portland to Grand Manan from 8 or 9 to 17, and thence to the bottom of the bay to 36. Prof. Bache's paper was illustrated with some very interesting diagrams and charts, shewing the wonderful coincidence of

the height of the tides in various places, with the lines of the coast."

Prof. Henry read a paper on

SOME PHENOMENA OF ICE.

"He said that they were in the habit of receiving all sorts of communications and curiosities at the Smithsonian Institution; and more questions were put them than many very wise men could hope to answer. One cold day in winter, a countryman was shown into his office, who said he had travelled 20 miles to bring him a curiosity. He proceeded to unpack it, and instead of an animal, as he had expected, he found it to be a milkpan filled with frozen water. On the top of the ice in it was a strange formation, created without apparent cause. A crystal of ice protruded from it in a slightly oblique manner, in shape almost like an isosceles triangle, with its sides somewhat curved. This crystal was found to be hollow. After ordering a drawing to be made of it, the matter was laid aside for subsequent consideration, and not again taken up until questions were subsequently put to him respecting the cracking of ice in very cold weather. It was well known that in the process of the solidification of melted metals, and the freezing of water, the crystals are produced in the direction of the surface from which the heat escapes. In the freezing of the water in a vessel of this sort, the crystals run in nearly horizontal lines, crossing each other at an angle of 60 degrees. The water, freezing first from the sides and bottom of the vessel, left in the centre and top a triangular space, which the yet unfrozen but expanding water found too small for it. It rose above the level of the ice, therefore; its edges freezing there again, the same phenomenon recurred, and the crystal was built. up. Ice having once been formed, however, followed the law of all other bodies, contracting with cold and expanding with heat. Thus it was that in very cold weather the ice was found to crack open sometimes with a loud report, the cracks taking place in the parts of least resistance, generally the narrowest portion of the body of water frozen over. The crystals formed on the surface of large bodies of water in the process of freezing were nearly perpendicular, the cooling surface being that exposed to the cold winds This was easily seen as the ice decayed, and the crystals separated the one from the other. The subsequent expansion of the ice by the recurrence of warm weather sometimes brought the edges of the fissures together, and crushed the newly-formed ice into a heap or