We find also that those coal carbo-hydrogens which afford most vapors are those which leave in their decomposition most allotropic carbon; the natural bitumens affording the most remarkable and convincing results in this way.

"As the mechanical state of the gas-carbon, clearly shown under the microscope, as well as to the unassisted eye, is that of a solid left from a transporting vapor, observation indicates that it has been thus formed in the very compound atmosphere resulting from coal decomposition.

"It is a fact of chemical science, that olefiant gas, when heated, deposits carbon, and the fact can be easily demonstrated. But it is a remarkable feature in this decomposition, that the gas deposits its carbon in the form of lampblack, and the utmost reach of the means of control will not produce an aggregation of particles resembling charcoal. In high, or comparatively low temperatures, the deposition never has the state of allotropic carbon, and, chemically speaking, there is no evidence that this form of carbon can result from olefiant gas changes.

"If, however, vapors of bitumen are mixed with the olefiant gas, these vapors suffer decomposition by heat, and we easily obtain in the mixture vesicular, brilliant carbon in the allotropic state of gas-carbon: while the vapors solely much more readily afford this substance, in form and composition closely resembling gas-carbon.

"The subject, as I have studied it, appeared to possess interest in connection with the new facts which M. H. St. Claire Deville has lately published, respecting the graphitic form of Silicon, Boron, &c., in which a similarity of conditions of production is essential to the effect being obtained.

"In geological theory, the formation of anthracitic carbon in one case, and of graphite, with the gradations back to anthracite, in another, has hardly been explained; but if we are allowed to take the allotropic state of carbon as a distinctive character of that carbon, which has been sublimed, through the agency of its own, or more likely a foreign vapor, then the occurrence of these forms of carbon ceases to be anomalous, and accords with the circumstances under which many rocks have been produced. Graphite, graphitic carbon, graphitic oxide of iron, and, in general, sublimates composed of vesicular forms presenting laminæ, under this view become a class of bodies which owe their forms to the transporting power of vapors in motion.

"Another point observed in the decomposition of olefiant gas deserves notice. It is stated in most treatises on chemistry, and adopted as a matter of belief in the gas manufacture, that olefiant gas, when heated, deposits two of its four proportions of carbon, and, without change of volume, becomes marsh gas. It is barely possible, as an accidental circumstance, this proportion of carbon might be deposited, but it would take place, not as an experimental, but as a chance result. When olefiant gas is passed through ignited quartz, glass, or iron-turnings, it deposits carbon, which has no definite relation to the composition of the gas, a mixed gas being left, containing olefiant marsh gas and hydrogen. If the gas is repassed, the carbon may be nearly all abstracted, the marsh gas suffering decomposition.

"The conditions of olefiant gas heated in the products of coal decomposition are not such as to lead to a breaking up of its carbon arrangement, for there are many reasons for the statement, that this bicarburet is itself the result of change in the vapor of paraffine and other hydrocarbons of the oily characters.

"It seems, therefore, a correct deduction from observation and experiment, that gas-carbon is not produced from olefiant gas by deposition, but is a product of changes caused by heat in vapors of hydrocarbons, and that this allotropic carbon, in other cases, forms in the presence of vapors, which can transport carbon in the vesicular

state."

Dr. Pickering referred to his having stated in print, that Manetho has given two distinct dates for the Fall of Troy: one of them (counting downwards in the Africano-Manetho Table) = B. C. 1127; and the other (in the Fragments preserved by Josephus, completed from the first-named source) = B. C. 1072. The earlier, being a Greek date, had always appeared doubtful, from the fact that Manetho was writing for a Greek Emperor. Since the publication of the above statement, Dr. Pickering has found that the Africano-Manetho Table contains both dates; the lower one in the Dynastic numbers, which (counted upwards from "B. C. 339," the adjustment supplied by Syncellus) give,

"9+38+20+6+124}+150+40+6+89+120+130"

= B. C. 1072.

In the Armenian version of the Eusebio-Manetho Table, the earlier date has not been found; but the lower date is regularly given in the Regnal numbers, for, counting downwards, – 5 — 68 — 40 — 194" = B. C. 1072.

B. C. 1413 11

"815

This lower date is confirmed by Ctesias, in his statement that the Assyrian Empire commenced 1000 years before the Fall of Troy, and lasted 1360 years: the dissolution of the Assyrian Empire being regarded by chronologists as fixed to the year B. C. 711, we have for Ctesias's date of the Fall of Troy,

= B. C. 1071.

B. C. 711" 1360 1000" Further, the Greek discrepance of Fourteen Olympiads, or fifty-six years, occurring equally in Manetho's Tables, may be fairly applied to his Greek date of B. C. 1127: when,

B. C. 1127 — 56 = B. C. 1071,

Manetho's reckoning proves to be the same with that of Ctesias, and perhaps of the Greeks generally. Dr. Pickering thinks, therefore, that B. C. 1071 is within a year of the Fall of Troy; but has not ascertained whether the separate years. will now close the chronological gap mentioned by Clinton. If so, and the date proves correct, it will carry the invasion of Greece by the Heraclide to the reign of Solomon.

Four hundred and thirty-eighth meeting.

April 14th, 1857. - ADJOURNED STATED MEETing. The Academy met at the house of Dr. Hayward. The President in the chair.

The Corresponding Secretary read a letter from the Secretary of the Academy of Science of St. Louis, dated April 4th, requesting an exchange of publications on the part of the Academy.

Professor Lovering read the following report on the Hedgcock Quadrant, which was accepted and ordered to be placed on file.

"The committee appointed at the last meeting of the American Academy of Arts and Sciences to examine Hedgcock's Patent Quadrant, which was submitted to the Academy, have attended to the duty assigned to them and ask leave to report as follows.

"A full meeting of the committee was held on the 14th of March, at which Mr. Ayling was present. He then exhibited the new instrument, and attempted to explain the peculiarities and pretensions of it. The committee have handled the instrument, and have made themselves familiar with its construction; which, as compared with that of the ordinary quadrant, is defective in some points, and in others boasts a superfluous complexity which is the only thing original in the invention, or entitled to a patent.

"The claim made for the instrument, namely, that by it differences of latitude and longitude can be ascertained, rests upon no specified discovery of a new law in nature, and can be shown, when analyzed, to contradict the best determined laws. The reflecting quadrant is essentially an optical instrument. In optics there are only two ways known by which the direction of a ray of light can be altered, viz. reflection and refraction; and these changes of direction are the same for polarized as for unpolarized light. To maintain, therefore, that, when the images of an object have been brought into juxtaposition with the object itself, and the glasses clamped, this juxtaposition will not continue if the instrument is transferred to another place, and that the motion which must be given to the glasses to restore the juxtaposition will give the change of latitude and longitude, is to maintain neither more nor less than this, that the laws of the reflection and refraction of light, which have been verified wherever there has been an observer for the last two hundred years, are not constant any longer, but have recently changed with the geographical position, and in such a marvellous way as exactly to suit the special claim of this Patent Quadrant.

"In opposition to any testimony that may be adduced to prove that this instrument has ever done what your committee say that it is incapable of doing, the committee would simply urge the unanimous and overwhelming testimony of mankind, not only of scientific men, but also of all engineers, surveyors, travellers, and sailors who have successfully determined their position by means of any quadrant or sextant, not one of whom has ever discovered that every observation he took with a reflecting glass was erroneous to the full extent of the dif

ference between his latitude and longitude and some one standard place; as it must have been if the laws of light then changed with a change of parallels and meridians, and this Patent Quadrant is not a patent absurdity. Lastly, any change of latitude and longitude which could be detected with the new instrument by means of the assumed discovery in the laws of light, might also be found, and with equal facility, by means of any other reflecting quadrant or sextant; and certainly with greater accuracy, unless the construction of the Patent Quadrant is much improved. Hence Mr. Hedgcock's modification is, on his own principles, quite unnecessary.

"One absurdity naturally leads to other absurdities: the boldest of which here is another claim for the new instrument; viz. that by it the navigator can obtain his geographical position, whether he observes the sun in the heavens or a lamp in his cabin. This is a necessary consequence of any admission made in favor of the new instrument. For the laws of reflection, as far as direction is concerned, are the same for all light, artificial or natural.

"The committee would say, in conclusion, that they feel justified in rejecting the pretensions of this Patent Quadrant, as contrary not only to the universal teachings of science, but also to the constant experience of practical navigators; and that they regard the whole claim. as simply ridiculous, and the language, printed and spoken, in which the claim has been asserted, as unintelligible nonsense; and the whole subject, therefore, as unworthy of the further attention of the Acad

emy.

(Signed,)

JOSEPH LOVERING,

B. A. GOULD, JR.,

G. P. BOND,

J. INGERSOLL BOWDITCH."

Dr. A. A. Gould presented, in the name of the family of the late Dr. Amos Binney, a former Fellow of the Academy, the third volume of his work on American Helices, containing the plates, now just completed.

Dr. H. I. Bowditch presented, in the name of Major Alvord of the United States Army, a copy of his paper on the "Tangents of Circles and Spheres."

Dr. Holmes exhibited and explained a new model of a stand for a microscope, contrived by himself, in which the various