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in the Academy's set of their publications, moved, and it was voted,

"That the special thanks of the Academy be presented to these institutions for their marked interest and courtesy in this behalf, and for their very valuable gifts."

Mr. Thurber of New York, by permission of the Academy, exhibited an ingenious adaptation of the pantograph, by which partially paralytic persons, unable to write in the ordinary way, may write with great facility.

Four hundred and eighty-seventh meeting.

October 9, 1860.-MONTHLY MEETING.

The PRESIDENT in the chair.

Dr. Hayes, in presenting a "Report on supplying the City of Charlestown with pure Water, made by Order of Hon. James Dana, Mayor, by Messrs. George R. Baldwin and Charles L. Stevenson, Civil Engineers," remarked, that

Chemical analysis presents points of interest relating to the composition of the water of Mystic Pond. The results obtained on carefully selected samples of this water, recorded in the Report, show a great variation existing at different parts of the mass of water. The weights of solid matter found in a standard gallon, are 4.08 gr., 4.64 gr., 15.52 gr., 16.88 gr., and 58.64 gr. Below a certain depth, the nearly pure water of this pond reposes on a heavier saline water. Further observations have shown that this saline water, closely resembling sea-water, maintains a nearly constant level in relation to the purer water reposing on it, and that the saline diffusion is apparently very slight in amount, or very slow in point of time. Change of temperature does not cause an intermixture of the two kinds of water; as the lower stratum has a density superior to that of the pond-water at its greatest density, and, physically, the conditions of repose are nearly the same, so far as penetration is concerned, as if a saline sand-bottom held the place occupied by the heavier water.

This pond, containing two kinds of water, can support the plants and animal organisms of fresh water and of ocean water at the same time.

Its sedimentary deposits may contain the remains of both fresh and saline water forms of life within the same area, thus offering an interesting subject to the observation of the naturalist.

Chemically considered, these two differing masses of water in contact exert powerful action. The organic matter suspended and dissolved in the fresh water, brought into contact with the saline water, leads to a number of decompositions of compound bodies. All the phenomena exhibited by ocean water in contact with water passing through the earth and entering the sea below its surface, are seen in this pond most distinctly. Thus, the sulphate of lime becomes decomposed into a salt composed of hydrosulphuric acid and lime, this new salt reacts on oxides of the common metals to produce sulphides and carbonate of lime, or upon sulphates of alkalis, so as, in presence of an excess of carbonic acid, to produce carbonate and bi-carbonate of soda, which may enter into new forms of matter. A bright metal plate immersed in this water at a certain depth may be exposed for hours to the action of the water without change. But if the slip be allowed to pass deeper, so as to reach the saline water, in the lapse of a few minutes it becomes coated with sulphide of the metal. The engineers engaged in the observations on the pond lowered a long silvered slip of copper vertically, so it should pass through the mass of fresh and saline water. On withdrawing the slip, after some hours had elapsed, the line of contact of the masses of waters was permanently marked on the slip,-all above it was unaltered, all below was blackened on the copper side by the formation of sulphide of copper. It was extremely interesting to note that the band presented no gradation of chemical action. Within the distance of one fourth of an inch, action and no action were marked, and it was in this way, as well as by chemical analysis, that the fact of the masses preserving their places was learned. Down into the fresh water, to within twelve inches of the saline water, the taste does not indicate the slightest saline taint, and even nearer the mass which produces so powerful chemical changes, the water is nearly pure. There is manifested in this juxtaposition of two waters of unlike composition some of the minor effects of electrical action, and in considering the chemical changes which may be and are exhibited in consequence, it appears that such a condition would be sufficient to account for the production of many bodies, which have been supposed to result from more active agencies only.

Mystic Pond, as at present constituted, consists of a thick stratum of nearly pure water, resting on an undisturbed mass of saline water, closely resembling that of the ocean.

Professor Cooke exhibited some octohedral crystals deposited on a furnace product, which he had obtained accidentally while experimenting on the compound of zinc and arsenic. The crystals were so brilliant that their angles could be measured with great precision, and they gave the exact angle of a regular octohedron. The composition of the crystals as shown by analysis was, zinc 81.18, arsenic 18.82. Professor Cooke argued that the arsenic in the crystals was present mainly in the condition of impurity, and stated his reason for this opinion. He considered therefore the crystals as showing that zinc might crystallize in forms of the monometric system.

He also exhibited a counterfeit American gold coin, of a specious character, the gold abstracted from the interior being ingeniously replaced by platinum.

Professor Horsford gave additional details upon spontaneous combustion, and mentioned a case in which iron-turnings saturated with oil had been known to ignite.

Dr. Beck, calling attention to the fragment of Petronius discovered by him, and communicated by him to the Academy about a year ago (now published in the eighth volume of the Memoirs), read the following extract from a letter received from Prof. Hertz of Greifswalde.

"The ineditum which you have sent me has been these fourteen years lying in my portfolio. I found it in a codex of the Marciana, and copied it, but delayed publication. I am glad that you have, in part, given it more complete than my codex presents it. It is mentioned, however, earlier than the edition of Anthon, for which you may find the proofs, which I have not at hand in this little watering-place in the Baltic, in Goldast's Sylloge Adnotationum in Petronium. In many things, this Petronius agrees with Isidorus in his Origines, which, in my opinion, he has used; its importance for Gellius is, as I think, subordinate. It was my original intention to publish the piece with the readings of the Venetian MS. in the Rhein

Museum, and to accompany it with my remarks; and I delayed my answer to you until I might, with my thanks, send you a copy of my article. But when I commenced the work, I saw that the so-called Petronius had besides profane authors used patristic sources, of which, under the article Choirogryllus, you have yourself given an example. But to trace and investigate the single articles, time was wanting, and I wrote, therefore, to Professor Ritschl, to whom I had already offered my article, of my change of intention, and offered to communicate my copy, in case some one of his pupils should wish to render the fragment accessible to German philologists. An able young philologist in Bonn, Dr. Reifersheid, has undertaken this task, as Professor Ritschl has lately informed me, and in a week, when I shall be again in Greifswalde, I shall send my copy of the Venetian MS. to Bonn, and take care that you receive a copy of Dr. Reifersheid's article.

Professor Agassiz reiterated his opinion that what are called varieties by naturalists do not in reality exist as such. His recent study of the Echinoderms in the collection of the Museum of Comparative Zoology at Cambridge, had confirmed this opinion. He found a great abundance of divergent forms, which without an acquaintance with the connecting ones, and large opportunities of comparison, might be taken for distinct species, but he found that they all passed insensibly into each other. In reply to a question, he stated that he discarded the sterility or fertility of crosses from the tests of the validity of species.

Professor Parsons suggested that more extended observation might connect the received species by intermediate forms, no less than the so-called varieties.

And Professor Gray remarked that the intermediate forms connecting, by whatsoever numerous gradations, the strongly divergent forms with that assumed as the type of the species, so far from disproving the existence of varieties, would seem to furnish the best possible proof that these were varieties. Without the intermediate forms they would, it was said, be taken for species; their discovery reduced them to varieties,

- between which, but not between species (according to the ordinary view), intermediate states were to be expected.

Four hundred and eighty-eighth meeting.

November 14, 1860.STATUTE MEETING.

The PRESIDENT in the chair.

The Corresponding Secretary read letters received since the preceding meeting.

Mr. E. B. Elliott read a paper "On the Calculus of Affected Quantities," in which was proposed a general unit-symbol of mononomial form, intended to embrace as particular cases, and to define the several affective symbols of, single, double, and quadruple algebra.

Professor J. Wyman presented and gave an analysis of a paper by Dr. John Dean, on the minute structure of the spinal cord.

Professor William B. Rogers described a simple application of the camera lucida for obtaining twin drawings, suitable for combination in the stereoscope.

For this purpose the reflecting prism, movable along a horizontal rod, must be adjusted successively in the positions proper to the right and left eyes respectively, when these are directed upon the object. The two pictures projected on the horizontal paper below, and traced out in the usual way, will represent the two aspects of the object as seen by the right and by the left eye severally, and, when united by means of binocular combination, they will reproduce the object visually in all its original relief.

As connected with the same subject, Professor Rogers referred to an arrangement for the binocular analysis of a perspective physical line described by him some years ago in the American Journal of Science.

In this the line was placed directly behind a vertical plate of clear glass, while the observer, keeping his head in a fixed position, viewed the line with one eye at a time, tracing on the glass the projections corresponding to its appearance, as seen by the right and left eyes respectively. The projections thus drawn will, of course, when binocularly combined, reproduce the original perspective line. In the same manner, a more complex object placed behind the glass plate may be represented in its two projections by pictures capable of a perfect binocular combination.

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