and 10" respectively. The aperture of the finder is 62 mm. The whole instrument is an exquisite piece of mechanical workmanship, and for both design and execution the makers are entitled to the highest praise.

The construction of the object-glass, first offered to the Clarks, but declined by them because of the subsequent cutting in two, was accomplished by Merz of Munich. Its performance, using the Steinheil achromatic eyepieces, is an agreeable surprise. With either half the images are as sharp as with a good four-inch telescope. With the images superposed, there is a loss of the best definition; and this arises from the practical impossibility of adjusting the two halves of such an objectglass so that the images will be absolutely superposed. In actual observing, the greatest difficulty in the way of exact measurement is found in a want of similarity in the atmospheric conditions affecting two celestial objects which are supposably near enough to be influenced alike. Thus the two opposite limbs of the sun, except in the very best observing weather, do not maintain a steady contact together when heliometrically observed, but vibrate, alternately lapping over and receding from each other. In the observations of the last transit of Venus, this peculiarity presented the curious effect of a rapid breaking and forming of a ligament analogous to the black drop' described by the older observers when the limbs of Venus and the sun were in contact.

The model on which the whole instrument is constructed is a very great improvement on any previous heliometer, so far as lessening the observer's fatigue is concerned. Every motion is controlled, and every scale and circle is read, by the observer without leaving his

seat.

With the cylindical bearings of the objectglass cells, the image distortion for measures up to 2° is rendered extremely small; by the rapid rotation in position angle, and equal rapidity in distance settings, the observer is no longer fatigued by manipulation; and it can be said that in this instrument the heliometer shows itself to be a measuring-machine of the highest precision. LEONARD WALDO.

NOTE ON THE OBSERVATIONS OF THE TRANSIT OF VENUS, 1882, AT THE LICK OBSERVATORY.

By invitation of Capt. R. S. Floyd, president of the trustees of the James Lick trust, I went to Mount Hamilton to direct the observations of the transit of Venus at the Lick

Observatory. The chief instrument of the equipment which the trustees had provided in time for observing the transit was the horizontal photoheliograph, which is essentially similar to those employed by the American commission on the occasion of the transit of 1874, as well as that of 1882, and which are described by Professor Newcomb in the first part of the American observations of the transit of Venus of 1874. The Lick photoheliograph, like all the others, has an objective five inches in diameter; and its focal length is almost exactly forty feet. The heliostat mirror, an unsilvered disk of glass, is seven inches in diameter, and was mounted on a pier adjacent to that which supported the objective. A third pier, coming up in the interior of the photographic house, supported the plate-holder; and all three piers were laid up of brick, their foundation being in the rock of the mountain summit.

I arrived at the observatory in the evening of Nov. 21. The photoheliograph had, in the main, been mounted and got in readiness before that time by Mr. Fraser, the superintendent of construction of the observatory. It remained to complete the unfinished portions of the instrument, to mount and fully adjust the same, to modify some details which had been unsuitably constructed, and to make sure of the convenient and effective working of every part. Especial attention was given to the accurate determination of the position of the focal plane of the objective; and the method. adopted-being nothing short of a critical examination, by many persons independently, of several sets of trial-plates exposed at varying distances from the objective-finally indicated the true setting of the plate-holder with much more than the required precision. Great care was taken to insure the perfect definition and figure of all the pictures, and to prevent the mishap of fogged plates from scattering and extraneous light. Much time was consumed in this way in the preparatory work, but we had more than sufficient compensation in the superior character of the photographs of Venus in transit. All these were taken by the wet process, and the photographic operations were in charge of Mr. Lovell of Amherst.

During the important days of the transitperiod, the meteorological conditions on Mount Hamilton were especially favorable. At midnight, Nov. 30, the sky cleared, after three and a half days of continuously cloudy weathFrom that time until the afternoon of Dec. 7 we saw no cloud, day nor night, which could in the least interfere with any observation we had to make. Thin cirrus was float

er.

ing above the mountain summit on the morning of the 2d, but it had vanished completely within two hours; and on three or four occasions clouds were observed very near the horizon, but they never rose. Fitful gusts of wind prevailed night and day the 3d and 4th, and the morning of the 5th; but, about noon this latter day, a period of the utmost tranquillity set in, and lasted for fifty or sixty hours, the temperature ranging only between sixty and seventy degrees.

Dec. 6 the sun rose about seven o'clock, with Venus a good way on its disk. The first sensitive plate was exposed at eleven minutes after seven, the slit being three inches wide, and the exposure a second and a half long; but a very faint image was all that came out on the plate in developing. Six minutes later,

with an exposure of one second, a picture sufficiently intense for measurement was obtained; but the vertical diameter of the sun was about a quarter of an inch, or one-eighteenth part, shorter than the horizontal one. Something like a half-hour later, very satisfactory pictures began to be obtained, with the slit an inch wide, and an exposure less than half a second long. By twenty minutes past nine the slit had been reduced in width to 0.25 in., and was kept at this setting throughout the remainder of the transit, the exposures varying only slightly from 0.25 sec. in length. At twenty-two minutes before twelve the last exposure preceding interior contact at egress was made, and subsequently ten additional photographs were taken between the two contacts. The total number of plates exposed was a hundred and forty-seven, and about five

the photographs themselves, are now stored for safe-keeping in the vault of the observatory on the mountain.

No other observations of importance were attempted, except those of the two contacts at egress: these being observed by Capt. Floyd, with the twelve-inch equatorial, aperture reduced to six inches; and by myself, with the four-inch transit instrument. DAVID P. TODD.

A GIGANTIC WALKING-STICK FROM THE COAL.

WE owe to the favor of M. Charles Brongniart of Paris, sketches of an enormous insect from the carboniferous beds of Commentry, France, which we have reproduced upon this page; in short preliminary notices, given last December to the Paris academy and the geo

logical society of France, he has named it Titanophasma Fayoli. The interest attaching to this remarkable creature, which has not before been figured, and to another somewhat smaller species published by him five years since under the name of Protophasma Dumasii, is twofold. First: scarcely any group of Orthoptera is so specialized as the Phasmida, or walking-sticks; and one would naturally look upon these bizarre creatures as the last term in a long series of forms in a special line of development. They had never been found fossil, excepting in one or two fragments in amber, when suddenly the upper coal-measures of Commentry revealed a considerable number of forms, of which M. Brongniart has only described two. He points out, that they differ from modern types in certain features, such as the relative length of the parts of the thorax and legs; but their connection with living Phasmida is unmistakable. Second: the hind wings are of a type very different from those of living Phasmida, and accord closely, as pointed out in my paper on The early types of insects, with those of a whole group of detached wings found in carboniferous beds in Europe and America (Dictyoneura, Paolia, Haplophlebium). These have always been looked upon as Neuroptera. It can hardly be doubted that these wings belong to this early type of walking-sticks, a probability, we may add, strengthened by unpublished material in our possession. Here we have clear evidence of the presence, in early times, of synthetic types of marked character. M. Brongniart informs me that he has now over five hundred and fifty specimens of arthropod remains from Commentry alone, and as our own Mazon-Creek beds have doubtless yielded as many, we may look for many new revelations concerning the early insect fauna of our globe. I am already acquainted with half a dozen or more species of Dictyoneura and allied genera from our American coalfields, notably from Pennsylvania. The figures we give are from M. Brongniart's sketches, reduced lineally one-half. The body is that of the original specimen of Titanophasma described in the Comptes rendus of Dec. 11. The wing, his latest discovery, and not yet described, has merely been mentioned by M. Brongniart, in the bulletin of the entomological society of France: it was found detached in the same beds, and is conjectured by him, not without reason, to belong to the same or a closely allied species. Of Protophasma, specimens have been found with the wings attached to the body. SAMUEL H. SCUDDER.

As

ANATOMY AND HISTOLOGY OF

POLYOPHTHALMUS.

THIS interesting genus, which was first discovered by Dujardin in 1839, and more fully described by Quatrefages in 1850, is the subject of a fine monograph by E. Meyer in the Archiv für mikroskopische anatomie, xxi. 769. The transparent worm is 15-18 mm. long; has twenty-eight bristle-bearing segments, followed by eight smooth, very small ones, none of which are marked externally. The bristles form two rows on each side. Most remarkable are the eyes; of which there are three on the head, and several pairs on the body. In P. pictus, the species investigated by Meyer, there are twelve such pairs, on as many segments. The external cuticula is of nearly uniform thickness, except over the sensory organs, where it is thinned out; but the hypodermis varies considerably, and is composed of narrow cylinder cells and relatively large unicellular glands, which last have granular contents, an oval nucleus, and a cross-shaped opening through the cuticula for the duct. The external coat of annular muscles is very imperfectly developed. The remaining muscles resemble those of other annelids. The bristles arise from the bottom of four pockets in each segment; the pockets (bursae) are invaginations of both the hypodermis and cuticula; but the hypoderm cells are cubical, and not cylindrical as over the rest of the body. The brain is kept in place by a set of threads of muscular and connective tissue, which run from various points of the body-wall to the cerebral envelopes. A detailed description of the nervous system is given. The ventral cord is nearly uniform, and has no distinct ganglionic swellings. It lies close against the skin, which directly underneath it is reduced to a thick cuticula with a matrix of flat cells, which pass suddenly on either side into the

The

layer of hypodermal cylinder cells. There are two pairs of peripheral nerves in every segment. sensory organs are numerous and interesting. The organs of touch are the cephalic and anal papillae. The former is a small elevation of the integument of the forehead, covered with a delicate cuticula and thin hypodermis, and receiving a number of nerve filaments. The nine anal papillae are similar in structure, but project more. There are also the socalled lateral organs, a pair in each bristle-bearing segment, which are probably homologous with the seitenorgane discovered by Eisig in the Capitellidae. They lie between the two bristle pockets of each segment, and have the form of hemispherical projections, probably covered in life with free sensory hairs arising from the modified hypodermal cells, which rest upon a peripheral ganglion, from which they are separated by a thin membrane; the membrane is pierced by the cells to establish their connection with the ganglion. There are beaker-shaped organs, having evident resemblance with those of fishes and the Capitellidae, but present only in a single cephalic pair. There is also a pair of ciliated pits of horseshoe shape on the oral segment. These pits are in structure quite complicated; and their bottom has hair-bearing sensory cells, which are greatly elongated, have rod-like nuclei, and rest upon a ganglionic layer, to which runs a large special nerve. There is

an evident histological similarity between the ciliated pits, the beaker-shaped organs, and the lateral organs. The lateral eyes are of two sizes, those upon the eighth to the fifteenth segments, both inclusive, being nearly twice as large as the four other pairs: they all lie close against the integument, the overlying cuticula and hypodermis being both very much thinned. The

oval lens lies close against the hypodermis, and can be strongly stained with haematoxylin. From the inner surface of the lens depend a cluster of prismatic cells, with nuclei in their bases, or ends away from the lens. These cells fill up the interior of the eye, and are enclosed in an envelope, which is fibrous, pigmented, and nucleated. The fibres probably are, in part at least, ramifications of the eye-nerve; the envelope is separated from the inner cells (so-called glasskörper) by a limiting membrane. These eyes conform, therefore, in their structure, with the known type of annelidan eyes. The three cephalic eyes are embedded in the brain. Their most remarkable peculiarity is the extension of the envelope of the eyes over the lenses, where it is much thickened. Each eye has three lenses (in P. pictus), but otherwise is similar in structure to the lateral eyes. Three pear-shaped vesicles lie beside the eyes: these Meyer believes to be probably otocysts. The digestive tract has five divisions: 1°, the mouth cavity, is a rather long cylindrical tube; 2°, the pharynx, extends in many windings and folds to the end of the fifth body-segment; it is quite muscular, and has numerous peculiar glands opening into it; these two parts appear to correspond to the fore-gut, while 3o, the oesophagus, seems rather a portion of the midgut, since it is lined with ciliated epithelium; 4°, the largest division or stomach proper, which has two ventrally placed glandular coeca at its anterior end; the coeca are lined with an epithelium composed of two distinct kinds of cylinder cells; the stomach has an external wall of fibrous and connective tissue, within which is a close network of large capillaries, which gradually becomes more and more irregular posteriorly; the epithelium over the capillaries is ciliated, but over each mesh there is a single cell, which extends down between the vessels, and itself forms a complete glandular bag, and represents a hitherto unknown type of cell-form; 5o, the endgut, is very short. The vascular system is well developed, and is described in detail. A short account of the body cavity is given; the structure of the segmental organs was not elucidated. The sexual organs have been accurately described by Quatrefages and Claparède. C. S. MINOT.

THE GLACIAL THEORY BEFORE THE PHILADELPHIA ACADEMY.

Ar the meeting of the Academy of natural sciences of Philadelphia, Feb. 13, Prof. Angelo Heilprin, referring to the subject of glaciation, stated that in his opinion the vast ice-sheet which is generally supposed to have covered, during the great ice age,' a considerable portion of the northern region of the European and North American continents, could not have had its origin, as is maintained by most geologists, in a polar ice-cap; since it may be reasonably doubted whether any accumulation of snow and ice in the far north could ever have attained a magnitude (in height) sufficient to have propelled a glacier with an estimated thickness of several thousands of feet, to a distance of hundreds of miles, and up mountainslopes to an elevation of five or six thousand feet.

The height of such snow-accumulation must necessarily depend upon two circumstances: 1°, the quantity of aqueous precipitation; and, 2°, the upper limit in the atmosphere to which clouds may attain. It is well known that as a rule clouds rise highest in the regions of highest temperatures, the equatorial, - where the vapor absorption by the atmosphere is greatest; and, for a similar reason, higher in summer than in winter. The minimum rise will therefore

take place in the polar regions, and necessarily during the polar winter. High (discharge) clouds in the extreme north are stated by arctic explorers to be a rarity, and hence precipitation in the form of snow must be restricted to a comparatively low atmospheric zone.

No great accumulation of snow can take place above this zone, which must consequently be of the height of the ice-cap. As a matter of fact, the officers of the late arctic expedition under Sir George Nares observed that the crests of the greater elevations were devoid of snow, and that in the winter-months there was altogether, even in the low lands, very little precipitation, heavy precipitation beginning only with the spring-months. The greatest snow-clad elevation in Greenland is Washington Land, supposed to be 6,000 feet, which gives origin to the great Humboldt glacier. Although this peak is completely buried in snow (of undetermined thickness), it may be safely doubted whether, unless with a warmer climate, snow of any great thickness could possibly accumulate on a summit of much greater height. If not, the elevation, in the opinion of the speaker, was entirely inadequate to account for the phenomenon of glacial propulsion southward to the extent required by geologists.

Prof. H. Carvill Lewis remarked, that, notwithstanding the difficulties in the way of a theoretical explanation, the fact of a great continuous glacier at the time of maximum glaciation seemed clearly indicated, at least in America, by the numerous observations recently made. He described the extent of the glacier in America, as indicated by its terminal moraine, and stated that the close similarity of its phenomena at distant portions of its southern edge indicated a continuous ice-sheet. The continuous motion of its upper portion is shown by the uniform direction of glacial striae upon elevated points. Thus the southwest direction of the striae upon the mountaintops of northeastern Pennsylvania was identical with that upon the Overlook Mountain of the Catskills and that of the Laurentian of Canada. The striae at lower elevations conformed more or less to the valleys, and did not indicate the general movement of the ice. The thickness of the glacier increased northward, the rate of increase diminishing as its source is approached. This latter point has not heretofore been appreciated, although observed some time ago by Dr. Hayes in the case of the Greenland glacier.

Recent observations by the speaker in Pennsylvania had shown the glacier to be 800 feet thick at a point five miles north of its extreme southern edge, and 2,000 feet thick at a point eight miles from its edge, while it was only about 3,100 feet thick one hundred miles farther north-east, and about 5,000 feet thick three hundred miles back from its edge. The amount of erosion it caused upon rock surfaces was in some degree a measure of its thickness, being far greater in Canada, even upon the hard Laurentian granites of that region, than in Pennsylvania, where even soft rocks were but slightly eroded.

The present thickness of the glacier in central Greenland was considered, and the magnitude of certain icebergs detached from it given. A friend of the speaker had within a few months seen a floating iceberg near the coast of Newfoundland which stood 800 feet above the water by measurement, and may have been therefore nearly a mile in depth. Dr. Hayes saw an iceberg aground in water nearly half a mile deep.

That the great glacier flowed up steep inclines, was abundantly proven by recent observations of the speaker in Pennsylvania. He instanced the striae

covering the north flank of the Kittatinny Mountain; and a bowlder of limestone perched on the summit, which, within a distance of three miles, had been carried up eight hundred feet of vertical distance.

Referring to a paper recently published by Mr. W. J. McGee, who found difficulties similar to those of Professor Heilprin in the assumption of a polar icecap of great thickness, and who imagined the glacier to increase by additions to its outer rim, Professor Lewis held, that the single fact of the transportation by the glacier of far-travelled bowlders to its terminal moraine was a fatal objection to any such hypothesis. Nor did he believe that the hypothesis adopted by Professor Dana and others, of a great elevation of land in the north, was a probable one. The facts now in the possession of geologists do not indicate such a great and local upheaval as required by that hypothesis.

-a

An explanation therefore must still be sought for the southward flow of a continuous ice-sheet, flow in some regions up-hill. The action of gravity was certainly not sufficient. Even in the case of the downward flow of the steeply inclined Swiss glaciers, it had been shown that gravity was more than counterbalanced by friction of the sides and bottom, and those glaciers moved by reason of an inherent moving power of the molecules of the ice. It was probable that a similar action occurred in the great continental glacier. He suggested, therefore, a hypothesis which, while preserving the unity of the glacier, as indicated by observed facts, neither assumed an unreasonable land-elevation in polar regions, nor required a thickness of ice so great as to be open to the objections of the last speaker. He suggested that the ice-cap flowed south simply because it flowed toward a source of heat. Such flow does not depend upon gravity, but would occur in a flat field of ice, or possibly even up a slight incline toward a warmer temperature. Upon this hypothesis the ice need not to have been more than a few times its present thickness in Greenland to account for all existing phe

nomena.

AN EARLY STATEMENT OF THE DEFLECTIVE EFFECT OF THE EARTH'S ROTATION.

A CORRECT knowledge of the deflective effect of the earth's rotation on the motion of bodies on its surface is generally accounted the result of studies made within the last twenty-five years. First in 1856, and more fully in 1859, Mr. William Ferrel of Nashville, Tenn., now of Washington, made the general statement, that," in whatever direction a body moves on the surface of the earth, there is a force arising from the earth's rotation which deflects it to the right in the northern hemisphere, but to the left in the southern" (Math. monthly, 1859, i. 307); and gave, by a rigorous analytical treatment of the question, a quantitative measure of this force, showing that it depended on the sine of the latitude of the body, but not at all on the direction of its motion. A similar but less comprehensive result was arrived at about the same time by Babinet and others (Comptes rendus, xlix. 1859); and since then the subject has been treated by many writers, among whom may be mentioned Buff, Finger, Guldberg and Mohn, and Sprung. It has, however, also been disputed by some authors, as Bertrand and Benoni, who erroneously hold to the old idea, first suggested by Hadley (1735), and recalled (it would seem independently) by De Luc (1779), Dalton (1793), and Dove (1835), that the deflective effect is greatest on motions in the meridian and nothing

on east-and-west lines; and this incorrect view is but slowly disappearing from the text-books in general

use.

It is the object of this note to call attention to an early statement of the law of deflection, that has never, so far as I can learn, received due credit. In 1843 Mr. Charles Tracy, now of New York, read a paper On the rotary action of storms' before the Utica (N. Y.) society of natural history; this was published in the American journal of science (xlv. 1843, 65-72), and the paragraphs quoted below are taken from it. It will readily be perceived that this explanation is far in advance of Dove's; although it lacks the consideration of the effect of centrifugal force and of the preservation of areas, to be a full statement of the matter. Mr. Tracy thought, in accordance with Espy's theories, that there must exist "a qualified central tendency of the air, in both the general storms and the smaller tornadoes" (p. 67); and in order to develop a uniform rotary movement in these centripetal winds, he looked to "the forces generated by the earth's diurnal revolution" (p. 66). In every storm, "the incoming air may be regarded as a succession of rings taken off the surrounding atmosphere, and moving slowly at first, but swifter as they proceed towards the centre." In virtue of the law of deviation, every ring "begins to revolve when far from the centre, turns more and more as it draws near it, and finally as it gathers about the central spot all its forces are resolved into a simple whirl" (p. 69). The law of deviation is illustrated by appropriate figures for the two hemispheres, and is explained as follows. (Its direct application to the tornado and water-spout is probably incorrect, as Mr. Ferrel has shown.) "The relative motions of the parts of a small circular space on the earth's surface, by reason of the diurnal revolution, are precisely what they would be if the same circular space revolved upon an axis passing through its centre parallel to the axis of the globe. If such space be regarded as a plane revolving about such supposed axis, then the relative motions of its parts are the same as if the plane revolved about its centre upon an axis perpendicular to the plane itself; with this modification, that an entire revolution on the axis perpendicular to the plane would not be accomplished in twenty-four hours. Such plane daily performs such part of a full revolution about such perpendicular axis as the sine of the latitude of its centre is of radius. The plane itself - the field over which a storm or a tornado or a water-spout is forming - is in the condition of a whirling table. Hence the tendency to rotary action in every quarter of the storm is equal, and all the forces which propel the air toward the centre co-operate in harmony to cause the revolution" (p. 72). The special value of this statement lies in the proof that motions in all directions are deflected equally; but on account of the omissions above named only one-half of the total deflective force is accounted for. W. M. DAVIS.

LETTERS TO THE EDITOR. 'Mother of petre' and 'mother of vinegar.' CHEMISTS were not a little interested a few years since by the discovery, first announced by Alexander Muller in Germany, and afterwards by Schloesing and Muntz in France, that the formation of saltpetre in nature, and of other nitric compounds as well, is in some way connected with the presence and action of a living ferment,' much in the same way that the formation of alcohol in the brew-house or distil