diamond is 3.52. Besides the specific gravity the hardness will be decisive, both can be scratched by topaz. Topaz is more difficult to distinguish. Its specific gravity is 3.40 to 3.65, very near that of the diamond. In this instance, as well as in those of quartz and Zircon, an optical test is the most convenient. In 1858, the Brazilian ambassador Lisboa, presented a "diamond" at the court of Vienna. It had been admirably, cut in Paris, and weighed 819 carats. By experts it was valued at more than fifty. millions of francs. One of the mineralogists called in consultation applied a very simple optical test, and found the stone to be a topaz. He placed a lighted candle upon a table, walked about 12 to 15 feet away from it, and looked at the light through the diamond, which he held close to his eye. In every facet two little flames appeared side by side. As only those crystals have single refraction, which belong to the isometric system (in which the diamond crystallizes) the specimen under question, having double refraction, could not possibly have been a diamond. When looking in this manner at a candle, the diamond, as well as the paste will show but a single flame in each cut face. Paste can readily be distinguished by its inferior hardness, as topaz will scratch it.

Price. The price of diamonds is one that fluctuates, dependent upon the demand and supply. Within certain limits it may be regarded as definite, but when the value of very large stones is to be estimated, the same rules for its determination cannot be followed. Diamonds are usually separated into three classes, and they are termed as being "first water," &c. Besides these three, there is the boart and carbon. These two latter varieties are utilized for purposes of cutting, sawing, drilling, &c. They are sold by the carat as other diamonds. One carat of carbon costs about 6 dollars.

Diamonds used for purposes of ornamentation advance very rapidly in price as their size increases. If, for instance, one carat should cost 100 dollars, six carats will not cost 6 x 100 dollars, but 6 × 6 × 100 or 3600 dollars. This rule does not apply to inferior stones, but is followed, within certain limits, in determining the value of the best class of diamonds.

Independent of its high price, however, which is always a recommendation to the favor of civilized man, and woman too, the diamond will ever hold its own prominent position, on account of its great intrinsic value.

MOUND-MAKING ANTS OF THE ALLEGHENIES.

THE

BY REV. HENRY C. MCCOOK.

'HE following notes are substantially extracts from an article. printed in the Transactions of the American Entomological Society. They relate to the familiar mound-making ants which inhabit the mountain regions of the Atlantic States, particularly Pennsylvania. These are insects in form

as represented in the accompanying figures, the head and thorax being of a fallow or reddish color, the abdomen a glossy black. There are three forms of workers, the major, minor and dwarf, by whom the entire external economy of the formicary, and for the most part the internal also, is conducted. The females closely resemble the workers-major, but FIG. 1. Worker Major. The are larger, more robust, and in the virgin lines beneath the latter figure state are winged. The males are winged, show the natural length of the are smaller than the females, from three worker forms. whom they are further readily distinguished by the smaller head, an additional segment to the abdomen and the different form of the same. In the original paper these ants are referred to as Formica rufa, the name which they bear (identified by Frederick Smith, of the British Museum) in the collection of the Entomological Society. They very closely resemble these ants, but on the authority of Dr. Auguste Forel, the author of the "Swiss Ants" (Les Fourmis de la Swisse), to whom specimens were sent, they are referred to in the following notes as Formica exsectoïdes Forel, a new American ally of F. exsecta. Their habits do not greatly differ from those of F. rufa of Europe, but are nearly if not quite identical with those of F. exsecta.

It is further premised that the observations given below were made while encamped in the midst of a colony, or "ant city," of more than 1600 nests, situated upon the castern slope of Brush mountain, Pennsylvania. These nests are conical elevations of various sizes, the largest measured being fifty-eight feet around the base, twenty-four feet over the top, and forty-two

1 Vol. VI, 1877, p. 253, sqq. The entire paper is published separately by John A. Black, 1334 Chestnut street, Phila.

inches in height. The mode of building the hills, which are honey-combed with regularly placed tubular galleries, is as follows. The mason work was greatly stimulated by a shower of

FIG. 2. Female.

FIG. 3. Male.

rain, and was indeed scarcely observed (beyond excavations of the underground galleries) before the rain-fall.

Building Galleries.—1, Fig. 4 represents a covered way or gallery six inches long, which started on the foundation three or four inches below the surface of the field, and rose up toward the half

2

FIG. 4.-Covered Galleries.—1, horizontal gallery; 2, vertical gallery.

cone at an angle a little less than 45°. When first seen it was an open gallery or ditch, and was observed until it was entirely cov

ered over except one door or round hole near the top. The work progressed by the continuous addition of earth pellets to the outer edge. The pellets were carried in the mandibles of the ants, and were usually pressed into position. The springing of the arch was plainly seen, the two sides slowly approaching each other in irregular lines as shown at a a. Gradually two points drew nearer and nearer, until they well-nigh touched. It was quite exciting to watch now the delicate manipulation of the architects. Here comes a worker with pellet of larger size; she climbs the arch, reaches over, holding the while by her hind feet, and drops the ball of soil into the breach. The bridge is made. And now with surprising rapidity it is widened until the roof of the arch assumes the appearance indicated at b b. Circular openings or doors are habitually left in the work, through which the ants are moving back and forth, apparently working upon the inside to strengthen the arch. As sections of the building are completed these doors are closed, so that they are plainly but temporary arrangements for the convenience of the

masons.

On other parts of the foundation similar structures were going up. At 2, Fig. 4, was a section of a vertical column, one side of which had been cut away. It was two inches high, and one inch across. The ants were working upon this in the same manner as described above. They built not only from the bottom up, but from the sides across. The central opening in the figure was finally closed, leaving, when the work ended, the opening at the foot of the column. The circular gallery thus enclosed was onehalf inch in diameter, which is about the usual dimensions. The work of construction was not confined to the space which, as in the above cases, was the original site of the cone. Having occasion to lift up a fragment half the size of one's head, which had been thrown to one side, I saw that the section had already been made the nucleus of a new mound. Columns, corridors and halls, corresponding closely with those outlined upon the under face of the fragment, had been erected, which were thus quite united to the fragment. In one of the halls was a small collection of dead ants. The greater portion of one day was spent in studying and recording the work upon this one hill. Other drawings were made from different positions, but the method and result were the same. As the activity occasioned by the shower

continued for the remainder of our stay, I had full opportunity by subsequent observations to verify my notes.

Fig. 5 is another example of architecture drawn from the same broken hill. The figure represents a double gallery which was built up against the perpendicular side H of a hole cut by the spade in removing the cone. The gallery a a a was carried along the base of the side three inches, and then upwards toward the surface. The gallery was widened at two points, c c, to one and a half inches, as though intended to serve as store-rooms for cocoons. Galleries opening downward communicated with these enlargements. At e ants were arranging pellets along a projection on the side, for what purpose was not apparent.

My attention was next directed to a large hill, which with its surrounding hill-cluster was on my regular "list." I took this plan of keeping several hills under regular, daily, and indeed for much of the time hourly observation, for the obvious reason that thus I could become "acquainted" with the workers, could trace the work done, and confirm or condemn previous conclusions as the case might be. In this hill a track had been made by one of a herd of cattle grazing in the field. The foot of the steer had left an irregular depression measuring nine inches each way, in depth eight to nine inches, the lower margin being six inches from the base of the hill.

FIG. 5.-Covering a double gallery a a a, and chambers c c c. Engineering. The lower part of this track is shown at Fig. 6,