dant examples in the present day, as in the occasional use of old English or Gothic letters in decorative inscriptions. The imperfect name is probably APIZTON (Ariston), as found complete on the stamp of the dolphin type (No. 4), where it is also written in the ancient manner, from right to left, though the workmanship of the stamp plainly indicates that it belongs to a period long posterior to that during which Greek writing ran in that direction. No. 4. It has been stated, as the general supposition, that the names accompanying the official stamp were invariably those of the state official; but it appears probable that when the name appears in the genitive case, as it occasionally does, it may be that of the producer himself; while a second name, which often occurs, may be that of the stamping magistrate. On some of the most recent of these antique stamps the sigma () is written in what is called the square manner-that is, in nearly the form of a C, as indeed it is on late Greek coins. The theta () is also sometimes abandoned for the simpler and softer sound of S; and thus we find on some of these handles of amphora what ought to be OAZIOON (Thasión) written as ΣACION (Sasión). The Thasian money of late date has often debased spelling of a similar kind, as OATION for CAZION. It may be stated here the amphora of different states are, in many instances, easily distinguished by archæologists without reference to their description; for instance, the clay of Thasos differs from that of Rhodes or Cnidos in being lighter coloured, and also coarser. The Thasian vessels are also less baked than those of Rhodes. Such are a few of the points of general interest to be met with in the study of these broken remains of the ancient amphoræ that once contained the Thasian wine, in addition to the knowledge acquired through their evidence that the Greek states took upon themselves the regulation of the trade marks of the articles of staple produce, instead of leaving them at the mercy of the caprice or dishonesty of individuals. The site of almost every historic Greek city, whether at present occupied by a modern town or not, has in its vicinity some mound or mounds formed of the ancient refuse of the place, often consisting in great part of accumulations of broken pottery. It is in such of the mounds, on the high ground above the Piræus, that M. Stephanos Comanoudis, professor of Latin in the University of Athens, has discovered a vast number of the stamped handles of the amphora of Thasos, of which the illustrations of the present article are examples. M. Comanoudis proposes to publish the result of his archæological labours, which will form a very interesting volume, opening up several new channels of information concerning the ancient commerce of Athens, and the laws by which its transactions were regulated; among which may perhaps be found many hints for the better regulation of our own system of trade marks and stamps. THE EXAMINATION OF TADPOLES. As we are now in the midst of the season of tadpoles, our microscopic readers may be advantageously reminded of the researches of Mr. Whitney, laid before the Microscopic Society of London in 1861, and briefly described in a former number of this magazine. Mr. Whitney recommends the binocular microscope to assist in the process of looking into the tadpole, which should be placed on its back. He observes, when matters are thus arranged, "before us is the beating heart, a bulbous-looking cavity, formed of the most delicate transparent tissues, through which are seen the globules of the blood, perpetually, but alternately, entering by one orifice and leaving it by the other. The heart appears to be slung, as it were, between two arms or branches extending right and left. From these trunks the main arteries arise. The heart is enclosed within an envelope or pericardium. This pericardium is, perhaps, the most delicate, and is certainly the most elegant beauty in the creature's organism. Its extreme fineness makes it often elude the eye under the single microscope; but under the binocular its form is distinctly revealed. Then it is seen as a canopy or tent, enclosing the heart, but of such extreme tenuity that its folds are really the means by which its existence is recognized." To the right and left of the heart the lungs should be looked for, in which the circulation can be seen in the middle and later periods of its life. In its first stage the tadpole "respires exclusively by gills," which are very interesting organs to watch. Mr. Whitney considers that in the middle and later stages of the tadpole's metamorphoses, in which it is neither a reptile nor a fish, the "three large arteries which arise from the heart become the cephalic, the pulmonary, and the aortic trunks." The cephalic artery, he asserts, "receives into it small branches from the subdivisions of the pulmonary artery, so that there is a direct communication between these two vessels." The second trunk he considers the true pulmonary artery, which enters and is distributed through the lung; and the third trunk, he states, "also enters and passes through the lung, inosculating in its course with branches of the pulmonary artery, and then emerges from the floor of the lung to enter the abdomen, and with its fellow form the aorta or great systemic trunk." Previous observers had not arrived at results presenting so complete an aeration of the tadpole's blood during its active and carnivorous and even cannibal stage of existence; but Mr. Whitney was careful to examine specimens sufficiently transparent. The great obstacle to this is the opacity usually presented by the coil of intestine. Mr. Whitney tried purgative medicines as a remedy, but without effect. He succeeded, however, by placing his tadpoles upon water diet, when the intestine could receive little solid matter, and ceased to obstruct his view. When the tadpole is lying on his back, the liver is a lobed organ below the left lung; and still lower is the oval kidney, lying close to the caudal vein. The reader will be assisted in tracing the blood-vessels by another quotation from Mr. Whitney, who observes, "all these are closely connected with the corresponding lung. The upper one-the cephalic-runs along the upper edge of the lung, and gives off, in its course, a branch which ascends to the mouth. The cephalic artery continues its course around the lung (forming, to all appearance, the edge of that organ), until it suddenly curves upwards and backwards, and reaches the upper surface of the head, when it dips between the eye and the brain, towards which it is evidently travelling." Enough has probably been said about the two other arterial trunks, but those who wish for further details can consult Mr. Whitney's paper.* We may add that his most successful tadpole looked quite opaque when taken from a jar containing green weeds, but proved on examination to be perfectly transparent. He had no red blood, and his other fluids were equally colourless. * Quarterly Journal of the Microscopical Society, Jan., 1862. VARIABLE STAR OBSERVATIONS. BY GEORGE KNOTT, LL.B., F.R.A.S. IN endeavouring to lay before the readers of the INTELLECTUAL OBSERVER a short account of the method of observing variable stars, I am desirous, at the outset, of disclaiming any pretensions to originality in what I shall have to advance. For the substance of the following paragraphs I am principally indebted to various papers by N. R. Pogson, Esq., Director of the Royal Observatory at Madras, who has prosecuted this branch of research with much assiduity and deserved success. Preparatory to commencing operations on a variable star, the following equipment is necessary:-An approximate chart of its neighbourhood, and a list of stars whose magnitudes have been carefully determined, to be used as points of reference in fixing its magnitude at the several times of observation. The "comparison stars" should be lettered or numbered for convenience of reference, corresponding letters or numbers being affixed to them on the chart. Thus furnished, the observer compares the variable with such of the "comparison stars" as may not, at the time, too widely differ from it in brightness, and carefully estimates the differences in tenths of a magnitude. Several values, which, after a little practice, will be found to be fairly accordant, are thus obtained for the magnitude of the variable at the time of observation, and the mean of these is assumed as its magnitude for the night. For convenience I shall term these "nightly means." The preceding remarks will be best illustrated by an example, which I take from my journal. "Jan. 7th, 1862.-U Geminorum. Estimated equal to -b6d-5: e-10: f-13: (the differences being expressed in tenths of a magnitude)." The assumed magnitudes of the comparison stars" are as follow, b = 93: d=103:e = 110:f113:-hence, the resulting values for the magnitude of the variable are,-9.9:98:100:100:-the mean being 9.9, which is, probably, not very far from the truth. The next step in the process is to project all the "nightly means" on cross-ruled paper, taking the dates of observation for the abscissæ and the corresponding magnitudes for the ordinates. A curve is then drawn by hand evenly among the points thus laid down, so as to leave as few discordances as possible; this is termed the "light-curve," and the epoch of maximum or minimum, as the case may be, is determined by reading off the date on which the curve passes through its highest or lowest point. If, owing to slowness of change in the magnitude of the variable, the "light-curve" is flattened near the vertex, the date of maximum or minimum cannot accurately be determined by inspection. In such cases the following expedient may be adopted :-Bisect the lines joining points where the "light-curve" in ascending and descending passes through equal magnitudes; among the points thus obtained draw a curve, producing it till it cuts the "light-curve;" the point of intersection is assumed as the epoch of maximum or minimum. A discussion of several observed maxima or minima gives the period of the variable star, which, with the range of variation, is in some cases found to be remarkably irregular. I have thus endeavoured to give a general idea of the mode of observing variable stars. Various difficulties will doubtless suggest themselves to the reader as likely to occur in practice. Of these the most serious, probably, is connected with the obtaining charts and lists of "comparison stars." I am in hopes, however, that this difficulty will be before long removed by the publication of the Hartwell Variable Star Atlas, commenced by Mr. Pogson, at Dr. Lee's observatory, and now in process of completion at Madras. This valuable work will in all likelihood do much to popularize an interesting branch of inquiry, and one in which the zealous amateur may labour with every prospect of success. SPECULA FOR TELESCOPES.-DOUBLE STARS. OCCULTATIONS.-TRANSITS OF JUPITER'S SA TELLITES. BY THE REV. T. W. WEBB, F.R.A.S. THE process of grinding and polishing specula, whether of metal or glass, for optical purposes, is not merely a laborious or, at least, tedious one from the hardness of the material, but one of much difficulty from the extreme delicacy of some of the operations, and the impossibility of obtaining the highest perfection which art can accomplish, by any other than what may be termed an indirect mode of working. The circular disc of metal or glass has, in the first instance, to be ground on one of its faces to the required curve, by means of a tool of brass or iron of similar form to itself, and not much differing in size. This is effected by working one surface on the other, with a due intermixture of circular strokes and straight ones carried in all possible directions, employing as an abrading material moist emery-a mineral powder of an extremely VOL. III.-NO. III. |
