cite in the rock, a great number of specimens were tested for effervescence, and all showed it in a prominent degree. As the above analysis of Dr. Genth gave no carbonic oxide, on inquiry, he writes: "The rock is full of cracks and these are lined with a minute quantity of calcite. The portion of which I sent you the analysis was as nearly as possible selected from that which did not show this coating. * Still some of the 'Igni

tion' may be Co," &c., &c.

*

*

It is clear from the position of these calcite crystals that they cannot all be due to infiltrated solutions of calcium carbonate through cracks in the rock, because the individual crystals are isolated from each other.

Their occurrence is peculiar and will be the subject of future study. Three separate determinations of ignition were 3.65, 3.40, and 3.88 (average 3.64).

Average determination of CO,=1,49 p. c.

Annexed is the analysis, resolved into the ultimate constituents of the rock (including 1 p. c. out of the ignition for CO2).

Considering this collection of atoms as united into molecules in which the oxygen performs partly a linking and partly a saturating function, we may discover something as to the probable kinds of silicates contained.* The chemical units into which this analysis is resolved below represent the amount of bond satisfying work which each atom performs, so that the total amount might with propriety be considered the quantity of molecule constructing work performed. It is calculated by considering the number of atoms of each element present, multiplied by the quantivalence of

* On this subject see Report C, 1876, pp. 115 to 124.

the element. Thus a monad atom having but one bond or affinity, exerts a unit of constructive work in the molecule.*

The percentage weight of each element in the compound divided by its atomic weight and this quotient multiplied by the valence of the element will constitute what is here given as the number of its chemical units.

Calling a the atomic weight of the element, w the percentage weight, the valance, and n the number of atoms; we have

As the bonds of oxygen must be equal in number to the bonds of those elements which the oxygen links or saturates, it must be assumed that the sum of the bonds of the acid and basic atoms must equal the number of bonds of the oxygen. This last remainder, therefore, gives the amount of oxygen in the compound employed exclusively in a linking function, while the difference between the number of acid and basic atoms (=1.376) equals the number chemical units of oxygen which are employed in saturating the acid bonds in excess. Reduced to percentage of the rock in question

Of the rock there are p. c. of oxygen..
Of which the saturating oxygen is .

Leaving p. c. of linking oxygen

44.34

5.92

38.42

*[It must be distinctly understood here that these expressions do not give the total (chemical) energy of the compound, which, however, could be obtained by adding together the product of these units of molecule building multiplied each by the force necessary to disrupt its union.]

These represent in the rock-

p. c. of (SiO,) combined in ortho-silicates.

p. c. of (SiO) combined in mono-meta-silicates......

Total....

22.67

28.12

50.79

It is interesting to note in conclusion that the rational formula calculated for labradorite according to the modern chemical system and which regards this mineral as one of the para-silicates is

This might be viewed as a mixed ortho- and mono-meta-silicate* in which there are two molecules of the radical (SiO,) and one of (SiO). In the latter one of the atoms of O is employed in saturating alone, and the proportion which this bears to the total amount of oxygen in both radicals is evidently 1 11.

In Pyroxene all the silica is present as mono-meta silicic acid.

In a mixture containing exactly one molecule each of Labradorite and Pyroxene, there would then be:

That is, the number of molecules of Ortho- and Mono meta-silicic acid would be equal, or if the p. c. by weight of the latter were as above supposed, 22.67 in the rock, that of the latter would be in such a mixture, 27.17 p. c. which is very nearly that actually given.

On the Total Solar Eclipse of July 29th, 1878.

BY GEORGE F. BARKER.

(Read before the American Philosophical Society, Nov. 15th, 1878.)

The purpose of the present paper is to put on record in the Proceedings of the Society some account of the observations made by certain of its members upon the total solar eclipse of the 29th of July, 1878.

The expedition was organized in June, by Professor Henry Draper of New York, out of compliment to whom, his associates named it the Draper Eclipse Expedition. The party consisted of Dr. Draper as Director, with Mrs. Draper as assistant, who were in charge of the photographic and photospectroscopic work, as also of the observations with the slitless spectroscope; of President Morton, of Hoboken, to whom was confided the general observations, as well as those with the polariscope and pocket spectroscope; of Dr. Thomas A. Edison, of Menlo Park, who was to use his newly invented tasimeter. in order to determine whether it was

*See "Tables for the determination of minerals," Frazer. 1874.

possible to measure the heat of the corona; and of myself, who was to observe with the analyzing spectroscope with the especial object of ascertaining the presence either of bright or of dark (Fraunhofer) lines in the spectrum of the corona.

Rawlins, Wyoming Territory, had been selected by the Director as the observing station, because while it was near the central line of totality, it was also easily accessible, being on the Union Pacific Railroad, was a place of some size, having eight or nine hundred inhabitants, and was the location of the railroad repair shops of the Laramie division, so that in case of need, assistance in constructing or repairing our instruments could be had. Moreover, it had a bountiful supply of excellent water brought in pipes from the neighboring Cherokee mountain, which being of granite, yielded a pure product of inestimable value for purposes of photography. Previous experience in that region of country too, had assured Dr. Draper that the air there was dry, and hence that the chances of clear weather on the day of the eclipse were very considerable.

The expedition left New York on the evening of the 13th of July ; and, resting by the way at Chicago for a day, reached Rawlins at mid-night of the 18th. The apparatus and material, which had been sent on by express in advance, had already arrived and in apparently good order, though in all it weighed nearly a ton, After a day's reconnoitering, plans were perfected and arrangements made for the construction of a temporary observatory in which to shelter the larger instruments. An excellent site was selected by Dr. Draper, protected in great measure from the strong winds from the west which at times sweep over those mountain plains. In this building the telespectroscopes were erected, a portion of it being converted into a photographic dark room, and supplied with running water from the hydrant. The location of this observatory was determined to be latitude 41° 48' 50" N., longitude 2 h. 0 m. 44 s. W. from WashingIts altitude above the sea level was 6,732 feet. The tasimeter telescope of Dr. Edison was erected in an adjoining building, facing the west and about ten or fifteen feet distant.

ton.

The ten days of time which had been allowed for completing the preparations was found to be none too much. During a large portion of every day and most of the night, some or all of the party were engaged in adjustment of the instruments, in practice with them, in determining positions in photographic work, or in the numberless details necessary to success. On the night of the 24th, we were joined by the English astronomer, J. Norman Lockyer, F. R. S., and also by Professor James C. Watson, of the University of Michigan. Mr. Lockyer's work being mostly photographic, he was efficiently aided by Mr. J. B. Silvis, the owner of a photographic car traveling over the Union Pacific Railroad, which chanced at that time to be in Rawlins. Mr. Silvis not only most generously placed himself and his car at Mr. Lockyer's disposal for any experimental purposes entirely free of expense, but on the day of the eclipse, he allowed him to take the car to Separation, about thirteen miles distant, assisted him in observing, and returned with him to Rawlins the same evening.

The day of the eclipse was all that could be desired. The sky was almost without a cloud throughout, and the dew point was found to be at least 34° F. below the temperature of the air. The entire programme of observations was carried out as it had been arranged, and with singularly good fortune. "The results obtained," as summarized by Dr. Draper, "were: 1st, the spectrum of the corona was photographed and shown to be of the same character as that of the sun and not due to a special incandescent gas; 2d, a fine photograph of the corona was obtained, extending in some parts to a height of more than twenty minutes of arc, that is, of more than 500,000 miles; 3d, the Fraunhofer dark lines were observed by both Professors Barker and Morton in the corona; 4th, the polarization was shown by Professor Morton to be such as would answer to reflected solar light; and 5th, Mr. Edison found that the heat of the corona was sufficient to send the index beam of light entirely off the scale of the galvanometer." As these results seem to be of very considerable importance, it appears desirable to give the various methods of observation somewhat more in detail, adopting for the purpose so far as possible the language of the observers themselves, as given in their several reports.

PHOTOGRAPHIC AND PHOTOTELESPECTROSCOPIC OBSERVATIONS.

The instruments which were used by Dr. Draper in his photographic and phototelespectroscopic observations were: "1st. An equatorial mounting, with spring governor driving clock, loaned by Professor Pickering, Director of Harvard Observatory. 2d. A telescope of five and a quarter inches aperture and seventy-eight inches focal length, furnished with a lens specially corrected for photography, by Alvan Clark & Sons. 3d. A quadruple achromatic objective of six inches aperture and twenty-one inches focal length, loaned by Messrs. E. & H. T. Anthony, of New York; to this lens was attached a Rutherford diffraction grating nearly two inches square, ruled on speculum metal. This arrangement (Fig. 1.) with its plate holders, etc., will be designated as a phototelespectroscope. Besides these there was a grating spectroscope, an eye slitless prism

PROC. AMER. PHILOS. SOC. XVIII. 102. N.

Fig. 1.