The axial ratios of the three species are as follow:

65° 20'

64° 24'

111° 6'

111° 30'

The relations of the three species in chemical composition are spoken of in a later paragraph.

Chemical composition. The best available material was used in the analyses by Mr. Horace L. Wells; it was free from every impurity with the exception of the quartz, which was so intimately intermixed that separation was impossible. The presence of the quartz, however, did not interfere in the least with the accuracy of the composition finally deduced. The water was determined directly.

Two analyses gave:

Excluding quartz, the mean of the two above analyses gives:

100.41

1.

3.07

3.00

The ratio P,O,: RO: H,0=1:3: 3, corresponds to the formula Mn,P,O,+3aq, which requires the following percentage composition:

P,0 = 34.72

MnO = 52.08

H,0 = 13.20

100.00

It is interesting to note here that the same formula was deduced by M. Debray* for an artificial salt which he obtained in brilliant crystalline grains by boiling a solution of phos* Annales de Chimie et de Physique, III, Ixi, 433, 1861.

phoric acid in excess with pure magnanese carbonate. He gives, however, no description of the form of the crystals obtained.

The close correspondence of reddingite with scorodite and strengite has already been pointed out; chemically the relation is not so close, for the manganese is all in the lowest state of oxidation and only three molecules of water are present. The formulas for the three minerals are as follows:

Pyrognostics. On heating in the closed tube, whitens at first, then turns yellow and finally brown, but does not become magnetic. In the forceps fuses in the naked lamp flame (F=2). B.B. colors the flame pale green and fuses easily to a blackish-brown non-magnetic globule. Dissolves in the fluxes and reacts for manganese and iron. Soluble in hydrochloric and nitric acids.

Reddingite is named from the town in which the locality is situated. It was the last of the above species to be discovered, and we were led to make an especial search for it by finding black octahedrons implanted upon one specimen which were obviously pseudomorphs and which could not be referred to any known species. Another specimen exhibited pseudomorphs of the same species, but where the alteration was not so far advanced.

Concluding note.

8

In a second paper upon this locality which we expect to pub lish within a few months we shall describe under the name of fairfieldite a sixth new species, whose character has been determined too late to find a place in these pages. It is a hydrous phosphate of manganese and lime, having the formula R,P,O, +2H,O, where the protoxide elements are manganese and lime chiefly; also iron and soda in small quantities. Fairfieldite is a yellowish-white to colorless transparent mineral, with an adamantine luster on the surface of eminent cleavage; the hardness is 35, and the specific gravity is 3.15

We intend also to give descriptions and, so far as possible, analyses of the other associated minerals, as, rhodochrosite, hebronite, the black massive products of decomposition and other species of special interest.

ART. XII.-Observations of the Transit of Mercury, May 5-6, 1878; by L. TROUVELOT.

THE transit of Mercury over the Sun was observed at my Physical Observatory in Cambridge with the 6 inch refracting telescope by Merz, the full aperture being used during the whole time of transit. The power employed for the observations of contacts was 153, but for physical observations higher powers were found necessary. Even as high as 250 and 450 were found excellent during the afternoon. The chronometer was compared before and after transit with the Harvard College Observatory mean time clock.

On the morning of the transit the prospects for good observations were not promising, the sky being overcast with dense and continuous cirri which, however, allowed the sun to be seen through them most of the time. But in consequence of this state of the atmosphere the telescopic image appeared rather poorly illuminated; although, considering the circumstances the definition was fair and the image quite steady, the sun's limb appearing only a little diffused.

Half an hour before the predicted time for contact the sun's surface was carefully scrutinized, but no spots were seen; and although a few small scattered faculæ were visible later, none could be seen at the time, owing probably to the thick vapors in the sky. No trace of the granulations of the solar surface could be seen. The sky forming the background to the sun. appeared of a milky whiteness, a very unfavorable condition for the observation of Mercury before ingress.

From 22h 20m till the time of contact, efforts were made to find the planet outside of the sun, but with no success; although the telescope was directed exactly where Mercury entered the solar limb, and my sight must very likely have been directed several times where the visible planet was situated. At 22h 26m, the chronometer's beats began to be counted, and at 22h 28m 375, Harvard College Observatory mean time, the planet suddenly made its appearance, notching the sun's limb almost exactly where my sight was directed at this moment. The suddenness of the phenomenon created some confusion in my mind from which ensued a delay of perhaps one or one and a half seconds in my record of the time, so that most probably the true contact really occurred at 22h 28m 36-0, H. C. O. mean time.

Although the contact seemed to me at first to have been instantaneous, yet, some unexplained phenomenon must have taken place immediately before I saw the black notch on the sun's limb, as I distinctly remembered afterwards that my attention

was called to this particular spot by a something I cannot well define, but which made me aware of the approach of the planet. But the impression was so rapidly followed by the contact that I have no definite idea of it, and am consequently unable to describe it.

While the disc of Mercury was passing the Sun's limb, my attention was particularly directed to the observations of the physical phenomena. The luminous point on the disc and the luminous ring were eagerly sought for, but no trace of either of these phenomena was perceived. The two opposite parts of the sun's limb in apparent contact with the black disc of the planet were also carefully observed to see whether there would be any index of atmospheric refraction, but nothing indicating it was observed. It is true that at this time the vapors in our atmosphere were quite dense and the telescopic image faintly illuminated; in fact, the conditions were not at all favorable for such delicate observations.

As the time of internal contact was nearing, it became obvious to me that it would be very difficult to estimate the exact time of true contact by the observation of the breaking up of the cusps, as they did then appear very dark and indistinct, so I immediately concluded to observe the apparent contact when the black disc of Mercury would be in apparent contact with the sun's limb. This was done, and the phenomenon took place at 22h 30m 52-5, H. C. O. m. t.

I feel quite confident that I have recorded this internal contact within a second or two of its true occurrence. According to these observations, the time elapsing between the two contacts was 2m 16.5. At least a minute passed before I was certain of seeing a thread of light separating Mercury from the sun's limb. No ligament or black drop was seen, however, the dark appearance of the cusps and the considerable time elapsing between the apparent internal contact and the breaking up of the cusps would perhaps indicate that such a phenomenon took place; but if such was the case, the black drop could not have been as dark as the disc itself, otherwise it is likely that it would have been noticed, as I was in expectation of seeing such a phenomenon.

A few minutes after the internal contact, the disc of Mercury appeared pyriform and slightly elongated towards the sun's limb. This decided appearance of the planet continued visible for fifteen or twenty minutes; the major axis of the ellipsis being directed from northwest to southeast, it being a little inclined towards the east to the south of the path of Mercury on the Sun. This appearance was probably illusory, as later when the atmosphere was clear, the black disc appeared perfectly circular.

From the time of first contact till one o'clock in the afternoon, the sky became more and more cloudy and the observations consequently more difficult. During this time no traces of the inter-mercurial planets, or of the luminous ring were seen. However, I had a persistant impression of a faint nebulous cloud on or near the center of the black disc, but notwithstanding my efforts, I was not able to satisfy myself whether it was real or illusory.

At about three o'clock the sky cleared up, the definition was good; small faculæ and the granulations being well seen on the sun, Mercury was observed with much attention. At this time the planet appeared of an intense bluish-black color, much darker than in the morning. With the powers 250 and 450, the planet lost entirely the flat appearance of a disc, and its globular form became very conspicuous and striking; although no difference in the uniformity of its intense bluish-black tint was noticeable which could produce this phenemenon. The blackness of the disc appeared much more intense than the umbra or nucleus of any solar spot I have ever observed, and I do not think that any observer familiar with the appearance of sun spots, could for a moment be mistaken and take a round black spot for a planet in transit, so striking is the difference in character.

The small nebulous cloud observed in the morning on Mercury still appeared to be there in the afternoon, but while the vision had greatly improved by the clear sky, it seemed just as faint, ill defined and ghost-like as when the sky was vaporous. Great efforts were made to see a definite luminous point in this cloud, but nothing of the sort was visible. I was not able to convince myself of the reality of the phenomenon, and I am rather inclined to think it illusory from the well ascertained fact that the nebulous cloud was best seen in the afternoon when the image was slightly tremulous; but the moment it became steady, the phantom cloud vanished entirely, and the disc of Mercury appeared of a uniform intense bluish-black color.

During the whole time of transit, attention was given to the supposed inter mercurial planets which might have been in transit on the sun with Mercury, but no trace of such bodies could be detected, either by direct vision in the telescope or by projection on a screen. If such bodies do really exist and one or several were in transit with Mercury, their apparent diame ter must be very small, and at least less than one-half of that of the smallest solar granules, as a black object of this size could have been easily detected during the afternoon.

Although pretty well defined, the edge of the black disc of Mercury never appeared very sharp, even during the moments of best definition; nor did its outline appear perfectly smooth,