but his own will, and who has shewn in this act that he was unworthy of so noble a subject.

5. Fish of Mont Bolca.

At Padua we found the most complete collection of the fossil fish of Mont Bolca, probably in the world; over 500 specimens, generally presenting both sides, some of them five or six feet long, and all remarkably perfect. We visited this celebrated locality last Friday. It is in a very wild and romantic region, surrounded by lofty mountains. Mont Bolca itself is 2000 feet high; and to the north and east the Tyrolese Alps rise abruptly, leaving a profound and steep valley between them and the base of Bolca. Columnar basalt in regular forms crowns the summit, and intrudes between the vertical fish-beds.

6. Mineralogical Notes.

Sacacchite is a silicate of lime and alumina, containing fluorine, and occurs in square prisms highly modified.

Leucite occurs at Vesuvius in the older ejected blocks, as well as the most recent lavas, and it is observed in some instances undergoing a change to Ryacolite, while still retaining the external form of leucite, and sometimes cavities of ryacolite crystals are formed in the leucite.

Zircon occurs at Vesuvius in beautiful white and blue octahedrons in the old ryacolite gangue. Fluor spar occurs in octahedrons with hornblende in the older lavas.

Forsterite is identical with anorthite.

Davyne is regarded by Professor Sacacchi as a variety of Nepheline. The six-sided prisms are striated longitudinally, and are modified by a plane on the terminal edges, and another on the lateral; it occurs in a compact pyroxenite gangue, while the nepheline occurs in a gangue of ryacolite.

Arragonite is formed in an old mine at Monte Vasa from day to day, at a temperature below that of boiling water. Buratite comes from Campiglia in the Maremma Pisena in Tuscany, and not from Volterra.

Tourmalines of Elba. In the Grand Duke's collection at Florence there is a specimen 11 inches square, with four erect green tourmalines and one prostrate, 2, 4, and 24 inches long, and to 1 inch thick. They are associated with orthoclase and crystallized quartz. The pink tourmalines of Elba have always the basal plane OR, while the green prisms are terminated with rhombohedral planes.

Analcime? A singular analcime-like mineral occurs at Monte Catini, in which the soda replaces the magnesia, according to Professor Moneghini of Florence, who obtained for its composition—

[This result give the oxygen ratio for the protoxids, peroxids, silica, and water 1: 2: 6:11.]

Observations on the Zodiacal Light; with an Inquiry into its Nature and Constitution, and its Relations to the Solar System. By DENISON OLMSTED, Professor of Natural Philosophy and Astronomy in Yale College.* With a

Plate. Read before the American Association for the Advancement of Science, at the Annual Meeting at Albany, August 1851.

I submit to the Association a series of observations on the Zodiacal Light, made by me at Yale College from 1833 to 1839, upon the basis of which I propose to offer a new description of this mysterious phenomenon, and a brief inquiry into its nature and constitution, and its relation to the solar system. Particularly, I propose to inquire whether or not it is the origin of the meteoric showers of November and August. Various circumstances conspire to interrupt the continuity

* In next number of this Journal a particular account of the Zodiacal Light as seen in Southern Africa will be given.

of a series of observations on the zodiacal light, among which are the following:

1. The comparatively few nights in the year when, in our climate, the sky is cloudless, and the atmosphere sufficiently clear to afford good observations on a light so feeble and diffuse.

2. The low angle which the zodiacal light makes with the horizon for the greater part of the year while it is visible.

3. The presence of the moon, which entirely effaces it, and occasionally, for long periods, the presence of Venus or Jupiter, and sometimes of both planets. The light of Venus, especially, is often so bright, and the planet is so situated in the midst of the zodiacal light, as greatly to interfere with observations. Hence a number of years are necessary of diligent attention to the phenomena of this light, in order to become well acquainted with its habitudes and laws. Nor can I pretend to have made the best possible use of the opportunities afforded for viewing it, during the six years that my attention was directed to it. On the contrary, my observations were often interrupted by ill health, and other causes beyond my control. Still, they were sufficient to convince. me that my previous knowledge of this body was exceedingly defective, and my notions of it very erroneous; and the same may justly be said of most or all of the descriptions and graphic representations of it given in works of science.

I will therefore, first, attempt an accurate description and representation of the zodiacal light.

Since the direction of this body is oblique to the circles of diurnal revolution, and since it appears only immediately before or immediately after the sun, and therefore more or less of it falls within the twilight, consequently, its appearances are very different in different latitudes, being seen best of all in the tropical regions, where its direction always makes a high angle with the horizon, and where the twilight is short; and being scarcely visible in such high latitudes as London and Edinburgh, except near the time of the equinoxes. Hence British writers who have attempted a description of it, have usually given one that is altogether vague and inaccurate. The lower latitudes of our place of observation (41° 18′ 30′′)

afford a much better view of it, and my description and representation of it will conform to its appearance at this latitude.

I learn from my friend Professor Dana, that while with the exploring expedition in the torrid zone, he seldom failed of seeing the zodiacal light morning or evening, when not prevented by some of the causes before enumerated; but during the summer months in our climate we hardly see it at all. At the beginning of autumn we look for it in the morning sky, and at the end of autumn, in the evening sky. The state of the atmosphere most favourable for seeing it at its minimum intensity, is that peculiarly transparent condition which either precedes or follows a copious rain. The presence of a black cloud, also, near the horizon, frequently enables us, by contrast, to see more distinctly the faint diffusive light of the upper portions. With these advantages we may unite that of fixing one eye on a darker portion of the heavens a few degrees to the right or left, and looking askance with the other eye over the region of the object sought; this last expedient will usually be found useful for fixing its exact boundaries, in its various stages of intensity.

Although, as was first remarked by Mr E. C. Herrick, faint traces of the zodiacal light may be seen in the north-east early in August, yet it will hardly be obvious to common observation before the latter part of September. I quote from my record for September 25th, 1835 :—

"Observed the zodiacal light from 3 to 4 o'clock A.M. Very faint. Seen only by fixing the right eye on the region of Canis Major, and carrying the left eye along the ecliptic. Covers Regulus and the cluster in Cancer, and terminates a little south of Castor."

The earliest distinct view I have obtained of this body in the evening sky, was on the 21st November 1837, when I have the following record :

"Have constantly searched for the zodiacal light in the evening since the 13th inst. I imagined that that part of the milky way where this light would cross it was more luminous than common, but the light is ambiguous on account of the presence of Venus. But this evening examined in company

with three of my astronomical pupils, all distinguished for acuteness of vision. At 7 o'clock, Venus being near the horizon and hid behind a cloud, we could severally define the boundaries of the zodiacal light. By fixing the right eye on the milky way near Altair, and the left eye near the head of Capricornus, we could discern a pyramid less bright than the milky way, but still sufficiently distinct to be sure of its presence. Its upper edge grazed & and Capricorni and B Aquarii, its vertex reaching to the right shoulder of Aquarius; light very feeble and diffuse, but the triangular space between it and the milky way, embracing the Dolphin, perceptibly darker; elongation from the sun 90°."

As a description of the zodiacal light sufficient to guide the observer, I will offer the following: From the middle of September until the latter part of November, he will confine his attention to the morning sky. An hour and a half before daybreak (which is at that season of the year, in our climate, about 4 o'clock) he will first discern a feeble, diffuse, and scarcely visible light of a pyramidal figure, extending from the horizon upward through the zodiac to Gemini, covering Regulus and Presepe, and terminating a little south of Castor. Near the horizon its material is usually mixed up with the vapours that prevail there, so as to prevent its forming a definite boundary at its base; but from an altitude of a few degrees above the horizon, the light gradually declines until it fades into nonentity. Along the central part of the pyramid the illumination is greater than at the borders. From the greater length and amplitude revealed to us by circumstances peculiarly favourable for observation, we have reason to think that, on ordinary occasions, we do not see the whole of the body, but that it really extends farther than its visible boundaries, both in length and breadth. If the observer continues to watch this body from the middle of September onward through the month of October to the middle of November, he will perceive that the vertex or visible terminus moves along through the order of the signs, and nearly at the same rate with the sun, appearing, on the 25th of October, to occupy the space south of Denebola in the tail of the Lion, terminating a little above Regulus. From this time