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time. As the night came on and a temperature lower than the mean came up from the east and passed over, the lines of force would be inflected as in P or P, and a reverse variation of the needle to that which occurred before would now take place.

The natural effects of variation must be produced consequent upon the magnetic nature of oxygen and its daily variations of temperature is manifest; but whether they cause the observed variations, or are competent to do so, is a question that can only be decided after very careful enquiry. Observations are now made on the surface of the earth with extreme care in many places, and these are collated, and the average or mean result, as to direction and intensity of the earth's force, ascertained for every hour and season; and also many remarkable, anomalous, and extra results evolved. A theory of the causes of any or all of these variations may be examined first by the direction which the varying needle does or ought to assume, and then by the amount of the variation. The hypothesis now brought forward has been compared by the mean daily variation for all the months in the year at north and south stations, as Toronto and Hobarton, and at many others near to and far from the equator, and agrees in direction with the results observed far beyond what the author anticipated. Thus the paths described by the upper ends of free needles in the north and south hemispheres should be closed curves, with the motion in opposite and certain directions, and so they are the curves described by needles in north and south latitudes should be larger in summer and smaller in winter, and so they are:-a night or cold action should grow up in the winter months, and such is the case-the northern hemisphere ought to have a certain predominance over the southern, because of its superior temperature, and that is so:-the disposition of land and water ought to have an influence, and there is one in the right direction :-so that in the first statement and examination of the hypothesis it appears to be remarkably supported by the facts. All these coincidences are particularly examined into and stated in the Philosophical Transactions already referred to. The next step will be to ascertain what is the amount of change in the conducting power of the air for given changes of temperature, and then to apply that in the endeavor to ascertain whether the amount of change to be expected is (as well as the direction) accordant with that which really occurs.

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ART. XI.-On Eupyrchroite of Crown Point, New York; by CHARLES T. JACKSON, M.D., Assayer to the State of Massachusetts, &c.

THE specimens of Eupyrchroite which I have analyzed were sent to me by Mr. C. F. Hammond of Crown Point, and he writes to me, that one hundred tons of the mineral have been taken from the mine, and it is understood it is to be employed in the preparation of phosphates for agricultural use. This enterprise has followed the movement which Mr. Alger has made at my suggestion, in working the mine of phosphate of lime in Hurdstown, New Jersey, and I hope it will awaken the attention of mineralogists and geologists to other neglected or overlooked deposits of this valuable mineral, so desirable as a fertilizer, and so important as a constituent of the vegetable products used for food. When the mode of managing this manure is generally known, there will be a demand for it that all our present known localities will not be able to supply, and therefore, every new discovery of any extensive deposit of it, will be hailed with pleasure. I learn that measures have been taken to export this mineral to England, where it is most highly valued for agricultural use, particularly in the preparation of the land for the growth of hops. It is also extremely valuable in the preparation of the soil for other crops, all of which contain phosphates in considerable proportions. It appears that the exhaustion of wheat lands by incessant cropping, without adequately replenishing the soil by manures, is owing to the removal of phosphates from the soil. Our farmers should therefore look into this matter, and remedy the evil that an early want of attention to the chemical principles of agriculture has led them into. It is hardly necessary for me to say that burned or ground bones may be used for the same purpose as the mineral I am about to describe; nor will it be necessary to enter upon the discussion of the question as to the indispensable necessity of the existence of phosphates in food, which is to form flesh, blood and bones, for most men know that they have seven pounds of phosphate of lime in their bones, and nearly as much of other phosphates in the soft parts of their bodies. It is also known that the ashes of all cereal grains contain almost fifty per cent. of phosphoric acid, united with lime, potash, soda and magnesia, and that plants derive these phosphates from the soil, which contains generally but a very minute proportion rarely amounting to three-tenths per cent.

Description and Analysis.

This mineral was first described by Prof. E. Emmons in his Report on the Geology of New York, and was analyzed by Prof. Lewis C. Beck and published in his Report on the Mineralogy SECOND SERIES, Vol. XII, No. 34.-July, 1851.

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of New York, p. 240; but his specimens differ somewhat from mine in their physical characters. It was named Eupyrchroite by Prof. Emmons in allusion to the beautiful emerald green light, which it gives out when thrown on heated iron, its phosphorescence being nearly equal to that of the chlorophane fluor spar of Connecticut.

The Eupyrchroite phosphorite occurs in botryoidal concretions, having a fibrous structure, and an ash-gray or bluish gray color, the concretions being made up of successive layers of different shades of color. Their surface is frequently covered with a delicate film of iron pyrites which scales off readily when scraped with the knife. Its Sp. Gr. is 3·053. Hardness 41. Before the blowpipe phosphoresces with a green light at first, then gives the intense brightness characteristic of lime salts. It glazes on the surface at a high temperature, but does not melt. In the glass tube it gives out water, which is acid, and corrodes the glass. When thrown in powder on metal, heated nearly to redness, it exhibits a brilliant emerald green phosphorescence. Larger fragments decripitate strongly.

During its solution in chlorohydric or nitric acid, it effervesces slightly, carbonic acid gas escaping. The quantity of this gas was accurately determined by the proper apparatus. In preparing the mineral for proportional analysis, each fragment was carefully examined with a lens, to ascertain that it was free from accidental admixture with other minerals. It was reduced to impalpable powder by levigation, and dried at 212° F., and weighed while still warm. A sample of the mineral in coarse powder was used in the determination of the water contained in it. In the other steps of the analysis the methods as given by Rose were pursued, and the following results were obtained.

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The fluorine as usual was expelled, and thus determined by difference, in the re-formation of phosphate of lime, after decomtion of the precipitated mixed phosphate of lime and fluorid

ium, and its equivalent of calcium was deducted from the tained as a sulphate of lime.

ART. XII.-On the Recent Condition of Kilauea; by Rev. C. S. LYMAN, including a letter from Rev. T. COAN, Missionary at Hilo, Hawaii.

In an article on "Volcanic Eruptions on Hawaii," published in the ninth volume of this Journal, (May, 1850,) the geologist of the U. S. Exploring Expedition* has given a description of the topography of this remarkable volcano, together with some notices of its various eruptions since it began to be visited by foreigners. To this article the reader is referred for a general description of the situation and character of the crater of Kilauea, illustrated by a plan and section.

The writer of these remarks spent several days at the volcano in July and August, 1846-some six weeks elapsing between the two visits.

A letter has just been received from the Rev. Mr. Coan, the enterprising American missionary at Hilo, Hawaii, whose name has been so often mentioned in connection with this volcano, sketching briefly the history of Kilauea since he and the writer visited it together in 1846. The volcano lying within the limits of Mr. Coan's missionary field, (though forty miles from Hilo,) he often has occasion to pass it in his tours among his people, and thus has become more familiar, probably, with its various changes and aspects for the last fifteen years than any other individual.

Before giving Mr. Coan's letter, it may not be improper to remark briefly on the appearance of the crater at the time of the writer's visits in 1846.

At that time the volcano was represented by Mr. Coan as being in one of its more quiet moods. Indeed, the first view obtained of it on our arrival was so little attractive as almost to produce a feeling of disappointment. The less curious class of visitors sometimes experience this feeling so keenly that they turn on their heel at once and refuse to descend into the crater, fully convinced that they have been deceived by extravagant descriptions, and that nothing is to be seen that will repay them for the trouble. On reaching the brink of the pit, instead of loud detonations and billows of fire, the ear heard nothing save the murmuring of the strong northeast wind as it rushed over the precipice, and the eye saw nothing save a broad, deep, enclosed valley-an apparently sunken tract of the earth's surface-with a black level bottom, strikingly resembling an area of burnt prairie land, from the distant extremity of which were lazily rolling up a few clouds of smoke and vapor, as if the prairie-fire were not yet wholly extinguished.

* See also Rep. on Geol. Expl. Exp., Chap. IIL

At night, however, that part of the crater from which the va pors had been seen rising was lit up with what seemed a glowing line of fire. This was the part of the volcano that has generally been called the "Great lake." Save at this point, the volcanic fires were nowhere visible from the upper bank, and only in a few other places were there seen indications of their existence in the jets of steam that were issuing from crevices in the lava. These steam jets, on further examination, were found to exist even out of the crater on the upper bank, in the vicinity of the huts in which visitors find temporary lodgings.

The northern sulphur banks we found to be essentially in the same condition as described by previous observers-lying under a bluff wall of rocky lava from which they are separated by a crevice or chasm, out of which constantly issue steam and sulphureous gases, depositing on the rocks, and even on the branches of certain species of vegetation, beautiful incrustations of sulphur and other substances.

Our place of descent into the crater was the usual one over the broken declivity at the northeastern extremity. On reaching the bottom, we found it difficult, at first, to identify any thing answering to the "Black ledge" spoken of in the narrative of the Exploring Expedition, and by most previous observers. In 1840 the crater, as described by Capt. Wilkes, and by Mr. Dana in the article already referred to, consisted of a sort of pit within a pita broad depression in the earth's surface, first by an almost perpendicular wall 650 feet in depth to the Black ledge, and thenleaving the ledge or terrace one or two thousand feet in width all around the crater-by a second abrupt descent of 350 feet or more to the general level of the bottom. In this lower area in 1840, were various pools of fluid lava, the principal one, known as the Great lake, lying towards the south western extremity, and measuring at that time 1000 feet by 1500 in diameter.

The terrace or Black ledge thus described we found almost obliterated, the whole interior of the pit having been filled up nearly to a level with it, and in some places from fifty to more than one hundred feet above it. By measuring a base line on the ledge and taking angles with a quadrant, the height of the northwestern wall of the crater above the terrace was computed to be 680 feet, which agrees nearly with the measurement of the Exploring Expedition, and shows that this part of the floor has not been elevated since 1840. Previous to the great eruption in that year, however, there is good evidence that the entire area of the crater, including the former Black ledge, had been repeatedly overflowed, and thus the ledge of the Exploring Expedition, (and which has remained unaltered to the present time,) placed at an

tion of many feet, (some observers estimate it at two hun

more,) above the Black ledge of Douglass and the earlier

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