With mixtures of isomorphous salts, however, the results were different. In these cases sudden crystallisation on touching with a nucleus producing a separation of both the sulphates apparently always in the proportions in which they existed in the solution. When gradual crystallisation took place with the sulphates of nickel and magnesium the nucleus increased by a deposition of the least soluble salt independent of the nature of the nucleus added. It may be seen therefore from these experiments that truly isomorphous bodies, that is, substances not only possessing the same form but also an identical chemical structure, may be regarded as active nuclei in exciting the sudden crystallisation of supersaturated solutions of each other. I hope shortly to extend the observations upon supersaturated solutions of mixtures, and of compound salts, employing their different constituents as nuclei, as I think by such experiments some light may be thrown upon the relations between these constituents when associated together in solution. There are, however, very few true double salts of which it is possible to obtain thoroughly supersaturated solutions. JOHN M. THOMSON

ON THE EARLY STAGES OF THE

CECILIANS

THERE are few groups of vertebrates respecting whose

life history and development so little is known, as the curious snake-like amphibians forming the order Peromela, and usually known as Caecilians. In all the ordinary zoological text-books in use in this country, the early stages of these animals are either left entirely unnoticed, or, at most, allusion is made to Johannes Müller's classical discovery of gill-slits in the young of Epicrium glutinosum. Even Prof. Huxley, in his article on the Amphibia in the first volume of the "Encyclopædia Britannica," published in 1875, after an allusion to Müller's discovery, states :-"It is to be regretted that nothing is known of the development of the Peromela" (loc. cit. p. 770). This being the case, it may be useful to call attention to two papers on the development of the Cæcilians, by Dr. Peters, the eminent German naturalist, read by him before the Royal Academy of Sciences of Berlin, and published in their Monatsberichte, as their contents seem to be unknown to, or overlooked by, the bulk of English zoologists. The first of these bears the date of January, 1874, the second was read eighteen months later (July 19, 1875). In the first of these Dr. Peters, after noticing the discovery by Müller of gill-slits in Epicrium, and its subsequent confirmation by himself (cf. Monatsbericht, 1864, p. 303) continues, "it was therefore extremely interesting to me to learn from Prof. Wrzensniowski of Warsaw, who last sammer honoured me with a visit, that some years ago the naturalist-traveller Constantin Jelski had sent him from Cayenne a gravid Cecilia, which after its capture had given birth to a young one, and had contained in its uterus several fullgrown embryos. Herr Wrzensniowski has now sent me for examination three of the young ones, and the old animal, referable to Cæcilia compressicauda (Dum. and Bibr.), and has givea with them the following notes, part of which are extremely interesting. These notes are extracted from a letter of Jelski's, dated from Cayenne, November 12, 1866, to Herr Taczanowski, the well-known Polish zoologist, in which he gives his account of an expedition to East Guiana, to a plantation called "Bon Père," belonging to a M. Lalanne, from which he had just returned. After narrating the method of fishing by means of nets adopted, and the great abundance of fish, Jelski continues"In the course of the hunt, the negro who was frightening the fish away from the bank, suddenly uttered a loud cry: we all saw something that looked like an electric eel swimming about with worm-like movements just under the surface of the water. M. Lalanne and I held back the negro, who was about to cut the animal into bits with his sword, the net was hauled up, and the creature landed. We all thought it was an eel, but on closer examination decided that it was a gigantic water-worm. I put the creature into a special vessel, and as I had already fish enough, and did not hope to obtain any others, went home. As I was taking this problematical creature out of the vessel, to put it into the calabash, I saw two of them instead of one. The old one had produced a young one. After I had laid the old one on the table, I examined it more closely; it exhibited very slow, tremulous, slight movements. Shortly afterwards I found it in true convulsions. I perceived that it was about to produce a second young one. I placed it in spirit, so as to convince people of its being viviparous. Membranes (Häute) were

ejected together with the first young one.' Herr Wrzensniowski adds-'After the receipt of the animal, I dissected it myself, and found in the oviduct five young, which I at once extracted, and two of which I send you together with the one that was born in Cayenne. All these examples that were removed from the oviducts were remarkable for a membranous outgrowth on the necks which was very easily torn off, and left a transverse linear scar, as in the specimen born in Cayenne, so that only a single specimen has retained this outgrowth till now. In the uterus I perceived nothing else noteworthy; the embryos lay in a dilatation of both oviducts, just as they now are in the spirit, without being covered by any membranous envelopes. I conclude therefore that the membranes, which, according to Herr Jelski, were extruded together with the young one from the oviduct were nothing else than the shed neck-vesicles (Nackenblase), which we could not find again in the parcel from Cayenne.'

sum.

"The female forwarded to me, whose oviducts had been removed, was fifty cm. long, and four cm, deep in the middle; its head measured three cm.; of the young ones, the newlyborn one, and one of the embryos, had a length of 157 millims., and a depth of twelve millims.; their heads measured eleven millims.; the other was only 136 millims. long and twelve millims. deep; its head was ten millims. They show no trace of the skinny vertical swimming-tail (Flossensaum) which both J. Müller and myself found on the hinder ends of the young E. glutinosum. But what surprised me much more was that there was no trace to be found of lateral gill-openings, like those which have now been discovered in several young examples of Epicrium glutinoThe head and fore part of the body in all three specimens lay bent back towards the sides of the belly, so that apparently in the uterus this curved part, that is the under side of the head, is closely applied to the body, and the end of the body also seems to have been recurved towards the sides of the belly. From the neck of the one specimen two smooth vesicles, fiftyfive millims. long, of irregular shape, and variously constricted, project; on them a blood vessel ramifies, whilst at their narrow transverse base they are connected together, though unfortunately no more can be learnt as to their original position, except that from their flat convex-concave form they are probably closely applied to the body.1 On the transverse scar, where the epidermis is absent, which these vesicles leave after falling off, on each side a small hole is visible, the lumen of one or two vessels, which are in connection with the aortic arches of their side. These vesicles therefore are external gills, which resemble the bellshaped external gills which Dr. Weinland discovered in the larvæ which develop in the external dorsal pouch in the female Notodelphys (Opisthodelphys) ovifera, and which he has described so well and thoroughly (Müll. Archiv, 1854, P. 457, Taf. xviii., Fig. 5, 6)." After some prefatory remarks on the distribution of the vessels to these bladder-like gills, Dr. Peters concludes:-"In any case, this discovery of a new agreement in the development of the Cæcilians with the other Batrachians is one of the greatest scientific interest, for in fact, not only is there now no doubt that, as in the Anura, so also amongst the Cæcilians a different gill-structure (Kiemenbildung) obtains, but it can also now be stated with certainty that in these animals also, for which the establishment of a third class or sub-class of Amphibians has even been proprosed, no amnion or allantois are developed, that, in part at least, they are viviparous, and that, at a certain period of the year, they are to be sought for, not in moist earth, but in water. Moreover, it is extremely probable that these animals, which only occur to fishermen rarely, and at a certain season, are not recognised by them, but are in fact shunned and destroyed on account of their ugly and wormlike aspect, and on this account so rarely come into the hands of collectors in their larval state."

In his second paper, read July 19, 1875, Dr. Peters contributes some further notes on the same subject, giving figures illustrating the young Cæcilia with its bladder-like gills still in situ, as well as the scars left on the neck after the fall of the gills, and the distribution and relations of the great vessels and aortic arches. The bulk of the paper is taken up with an account of the anatomy of the young Cæcilians, but a few additional remarks "As was on other points are given which we here reproduce. there (i.e. in his first paper) stated, in this species the embryos at birth are at most three and two-thirds smaller than the mother. It is also known that the young of Epicrium glutinosum, in which

This is also very probable from the observations of Weinland on Opisthodelphys ovifera, where the bell-shaped gills envelope most of the body.

the lateral gill-slits are still visible, are even larger as compared with the parent animal than is the case in Cacilia compressicauda. According to this, one might almost believe that such a relation in size is universal in the embryo Cæcilians. On the other hand, one might conjecture that a development with external vesicular gills, which obtains only exceptionally amongst the Anura, as in Opisthodelphys and Nototrema, occurred more commonly amongst the Cæcilians. The few observations however which have as yet been made on the other species of Caecilians do not confirm this. Thus A. Dumeril, in a young C. oxyura, 50 millims. long, has found on each side of the neck a branchial cleft, which it is true lies somewhat higher than in E. glutinosum, but still proves that in this species no external vesicular gills are developed (Mem. Soc. Sc. Nat. Cherbourg, ix., taf., I Fig. 8). Further, Prof. Möbius on the occasion of his late visit to the Seychelles, brought back several examples of C. rostrata (Cuv.), of very varying sizes (from 35 to 240 millims.) which have neither branchial clefts, nor a swimming-tail, nor do they show the scars on the neck that accompany the vesicular gills. All this leads one to conclude that the development of the Cæcilians, like that of the Anura, goes on in very various ways, and that in this field too important discoveries are still to be made. It cannot therefore be too deeply impressed on naturalists who visit tropical countries where Cæcilians are found, to give to this subject their especial attention."

PHILOSOPHY OF THE PUPATION OF SOME BUTTERFLIES1

THE comparatively sudden transitions from one state to another in insects, have always excited the keenest interest. The change from larva to chrysalis in those butterflies known as suspensi, and which in the chrysalis state hang from the tip of the body, has, perhaps, been looked upon as the most wonderful. The preliminary acts in the performance have been pretty well observed and described by various authors since the days of Vallisnieri. The larva hangs by the anal end, turning up the anterior part of the body in a more or less complete curve, and the skin finally splits from the head to the front edge of the metathoracic joint, and is worked back in a shrivelled mass towards the point of attachment. Now comes the critical feat which has most puzzled naturalists, viz., the independent attachment of the chrysalis and the withdrawal from, and the getting rid of, the larval skin which such attachment implies.

Réaumur explained it in 1734 by the clutching of the larval skin between alternate sutures of the soft joints of the chrysalis ; and his happy and circumspect account from observations made on Vanessa urtica has formed the basis for subsequent accounts; no one obtained a deeper insight into the philosophy of the act until, some two years since, Dr. J. A. Osborne, of Milford, England, discovered that a distinct membrane is concerned in it. In casual observations of the process I had long become convinced that the popular accounts were crude and inaccurate, and I had preserved specimens in the act of transforming, for future study; but the philosophy of the change cannot be satisfactorily made out from alcoholic specimens alone, nor from the study of one species. The present paper is based on observations made on species belonging to more than a dozen genera, the conclusions having been partially presented last June to the Philosophical Society of Wa hington.

The body of the larva is composed (exclusive of the head) of twelve egments or joints, and a sub-joint. It is with this subjoint that we have here to deal, for to it beneath the rectum are appended the anal pro-legs, and above this is the anal plate.

If we carefully examine the anal plates of the larvae of the true suspeni, we shall find that while they differ in form they have one feature in common, viz., the being furnished dorsally and po teriorly with numerous short spines and points generally retrorse, or so placed that the larva can make use of them in suspending. These special spines on the anal plate are only fully develed after the last larval moult, being more or less obsolete in the earlier stages, and they are also under muscular control. Even in the succincti, where, as a rule, the anal plate is not specialised, spines are, nevertheless, sparsely found, especially on the border.

All writers whom I have consulted speak of the larval suspension being due to the entanglement of the hooks of the anal pro-legs Abstract of a paper read before the American Association for the Advancement of Science, by Prof. C. V. Riley.

in the silk, and do not mention the use of the anal plate which the hillock of silk is sometimes spun in special form.1

The normal form may be likened to that of an inverted sets or shoe, or to a ships-knee, and one of the most interesting a of the larva, preliminary to suspension, is the bending working of the anal parts in order to fasten the back of the p to the inside of the back of the settee, while the crotchets of the legs are entangled in the more flattened position or seat some cases (as in Danais) the hillock of silk is more elongat and the spines of the truncate plate mostly occur around the bue margin and even beneath it, so that in fastening them the h seems to be drawing the silk up the rectum. In other cases a in Euptoieta) the plate, in addition to the spines, has a promine": tubercle on each anterior outer border well calculated to lo securely into the silk. After suspension, and as the fluids grat tate anteriorly, the silken hillock becomes more conical (th: threads being loosely spun and elastic) and the hooks both of the plate and the pro-legs hang more loosely from it.

In the final getting rid of the larval skin and attachment the chrysalis there are concerned

1. Certain factors belonging to the larva and cast off with is skin. 2. Those belonging to the chrysalis ; and to intellig explain the process it is necessary to more fully characterise d homologise these parts than has hitherto been done.

In the former category, in addition to the natural adhesives of the moist, mucous, and membranous corium, there are three physiological factors concerned: (1) the tracheal ligamen, 1 the shed trachea from the last or ninth pair of spiracles wh uniformly become blind or obsolete in the chrysalis; (2) the rectal ligament or shed intestinal canal; (3) the Osborne z retaining membrane (membrana retinens), which is but a stretche. part of the membranous coriam that accumulates around the rectum and in the anal pro-legs.

In the second category we have the structural features of the chrysalis. These are, first, the cremaster proper, which is the homologue of the anal plate of the larva, and the form of which is foreshadowed in that of said anal plate. This cremaster assumes a great variety of different forms, but in general may be said to be a tapering piece more or less incurved ventrally, and having the ventral and dorsal margins thickened or ridged, and these ridges may be respectively called the rentral and the dorsal cremastral ridges. This cremaster is surmounted at the apex and sometimes along the ventral ridges by what may be called the cremastral hook-pad, thickly studded with minute bet stout hooks, which are sometimes compound or furnished with barbs very much as are some of our fishing-hooks, and which are most admirably adapted to the purpose for which they are intended.

Secondly, we have the sustainers (sustentores), two projections which homologise with the soles (planta) of the anal pro-legs, and which take on various forms, but are always directed for ward, so as to easily catch hold of the retaining membrane. In the yellow butterflies (as Callydrias, Terias, Colias), where the body of the chrysalis is so thrown back that mere projecting tubercles would not suffice, we find them transformed into actual hooks; while in some of the succincti they are little more thas lepidopterous pupae these remnants of the anal pro-legs are mort a thickening of the anterior margin of the sub-joint. In al or less indicated, while in certain moths (Pterophorida) wher the pupa is partly suspended, they are, as in the Nymphalids. covered with long hooks similar to those at the tip of the

cremaster.

Thirdly, we have what may be called the sustentor ridge. usually connected with the sustainers, embracing them on the outside, and extending backward to the inside of the ventral ereforming quite a deep notch, which doubtless assists in catching mastral ridges, and sometimes, as in Paphia and Limenita, hold of the larval skin in the efforts to attach the cremaste

It is an interesting fact in this connection that Roesel, who has new had any superior as a delineator of insect larvæ, makes the Nymphalids a his figures all suspend to an elongate conical piece of silk apparently issuing from the anus, with the legs invariably free and in no instance hooked li is evident, however, from his text, that he was not aware of the use of the anal plate, and since he speaks of the larvæ attaching themselves by the hind legs or extremities, it is equally evident that his figures do not correspond with the text, while the freedom of the legs in his figures is, of course, a

error

2 What is here termed the corium is the membranous layer between the separating larva skin and the forming chrysalis. If, as recent investigat seem to show, it is only the outer half of the dermal layer of the skin whe is cast off in the exuviation of invertebrates, and not the whole skin with its three layers, then this membrane is developed between the splitting pars of said outer layer, and is not, strictly speaking, the corium.

hese sustentor ridges are homologous with the limb of the anal ro-legs and the exposed edge with the posterior border of said mb. They vary much in form, and may be more or less bsolete.

Fourthly, between them is what may be called the rectal piece, onsisting of a piece more or less well marked and elevated, specially around the closed rectum.

It is principally by the leverage obtained by the hooking of The sustainers in the retaining membrane, which acts as a swing ng fulcrum, that the chrysalis is prevented from falling after the eremaster is withdrawn from the larval skin. It is also princibally by this same means that it is enabled to reach the silk with the cremastral hook-pad. Yet the rectal ligament plays a most important part, and in some species a more important part even, in my estimation, than the membrane itself. The tracheal digaments which, from a study of specimens plunged in alcohol when the larval skin was about half shed, I was at first inclined to believe important auxiliaries, are, I am satisfied, of very little if any service in most cases. The rectal ligament is a constant physiological factor, and its importance cannot be ascertained by attempts to sever the membrane at the critical moment, because in such attempts the ligament is more or less drawn out beyond the power of the sphincter muscles in the chrysalis to control it.

now

Dissected immediately after suspension, the sub-joint_of_the larva will be found to be lying, especially between the legs and around the rectum, in an abundance of translucent, membranous material. An hour or more after suspension the end of the forming chrysalis begins to separate from the larval skin, except at the tip of the cremaster. Gradually the skin of the legs and of the whole sub-joint stretches, and with the stretching the cremaster elongates, the rectal piece recedes more and more from the larval rectum, and the sustentor ridges diverge more and more from the cremaster, carrying with them, on the sustainers, a part of the soft membrane. If a larva be carefully dissected at this stage, the forming membrane may be raised with the point of a needle, and stretched so as to show its connection with the rectal ligament; or it may be

lifted entirely from the retainers, when, by its elasticity, it contracts, and becomes more or less fully absorbed in the rectal ligament. It is at this stage that the strength of the latter may be fully tested, and if the chrysalis, flayed from the larval skin, and freed from the retaining membrane, be grasped in the neighbourhood of the rectum, so as to supply the natural holding power of the sphincter muscles, the rectal ligament will sustain, as I have abundantly proved, at least ten or twelve times the weight of the chrysalis; while it will support, if held by the larval skin, several times the weight of the chrysalis before separating therefrom. In brief, the retaining membrane is that part of the inner larval skin surrounding the pro-legs drawn down by the sustainers, and always intimately connected with and forming but a branch of the rectal ligament. When extended from its attachments, as when the chrysalis rises to the silk, this membrane dries, and in the cast-off larval skin retains more or less perfectly the stretched form. If the corium of the larva be thick and strong, as in Vanessa, the dried membrane will be broad, with two indentations where it was held by the retainers; if the corium be more delicate, as in Danais, Paphia, or Apatura, the dried membrane will be more forked, showing how the retainers have acted upon its elasticity. In every case, however, it shows, under the microscope, the longitudinal folds and creases incident to the stretching, and, compared to the rectal ligament proper, it seems to lose importance as it is less needed; for the succincti will generally attach when it is severed or loosened from the retainers, while in Apatura (at least as exemplified in the North American species), which combines the peculiarities of both the succincti and suspensi, it does not become specialised, and the chrysalis seems to rely almost entirely on the rectal ligament, assisted by the partial holding of the delicate larval skin, not only between what is left of the sustainers and the ventral posterior margin of the twelfth joint, but between the ventral sutures of this last and the preceding joint. And here I would remark, in conclusion, that the ventral borders of two or three of the joints preceding the subjoint are, in most chrysalids which I have studied, so hardened that the larval corium is actually

1

The larva of Apatura attaches horizontally, making the front pair of abdominal pro-legs answer the purpose of the girth; but in the shedding of the skin this attachment is severed, and the forming chrysalis assumes the perpendicular position, and in the withdrawal and attachment of the cremaster it acts as the true suspensi

grasped between them and the deep sutures made in contracting. In some instances (especially in some species of Papilio) the posterior border of the twelfth joint is produced into a medial transverse ridge fully as prominent as that formed by the sustainers, which here are flattened and coalesce; so that the sutures of some of the terminal joints in the chrysalis do subserve the purpose ascribed to them by Réaumur, but in a somewhat different way.

UNIVERSITY AND EDUCATIONAL

INTELLIGENCE

THE Oxford University Gazette of October 10 contains counsel's opinion on the proposed faculty of Natural Science at Oxford. It has been proposed that the University should, by statute, establish a new faculty, under the name of "The Faculty of Natural Science," should grant degrees of Bachelor and Master in that faculty, and should give to Masters of enjoyed by Masters of Arts, so making them Members of ConNatural Science all the rights and privileges which are now vocation (the governing body of the University), and enabling University. Mr. Horace Davey is of opinion that the University them to vote for the members returned to Parliament by the may create a new faculty in science, or (which comes to the same thing) may sever one of the sciences or philosophies formerly comprised in the Faculty of Arts, and may make it into a new faculty,, and grant degrees therein. Such a severance was anciently made in the case of grammar, rhetoric, and music. But Mr. Davey believes that the University has no power to confer upon graduates in a new natural science faculty the rights which now belong to Masters of Arts, and the degree of Bachelor or Master of Natural Science would not make the holder a Member of Convocation. This difficulty Mr. Davey suggests, might be avoided by the University conferring the degree of Master of Arts on any person obtaining the corresponding degree in the new faculty.

The new chemical laboratories at the Oxford University Museum will be opened for students this term. The chemical

department has now for many terms been overcrowded, and the

new buildings will not only afford ample space for beginners and pass-men getting up their "simple salts," but contain rooms set apart for special work and fitted with the best appliances under the careful superintendence of Mr. W. W. Fisher, Aldrichean Demonstrator.

The new chemical laboratory at Balliol College will be opened this term under the superintendence of Mr. H. B. Dixon. Balliol and Trinity Colleges have combined to equip and maintain this laboratory, and a physical lecture room for the use of their own

students.

At the University Museum Prof. Odling will lecture, this term, on Organic Chemistry; Mr. Fisher will lecture on Elementary Organic, and Mr. Donkin on Elementary Inorganic, Chemistry. Frof. Clifton will lecture on Elementary Electricity, and Prof. Story-Maskelyne on the Use of the Goniometer. Prof. Prestwich gives a course on two afternoons a week, on the Paleozoic Rocks, at the Museum, and Prof. Lawson will lecture on Vegetable Histology, at the Botanic Garden. Rev. C. Pritchard, Savilian Professor of Astronomy, will give practical instruction at the University Observatory, on fine evenings during the term; he will also continue giving public lectures on the history of astronomy. Dr. Rolleston will lecture n Circulation and Respiration, and practical instruction in anatomy and physiology will be carried on in the laboratory, under the superintendence of Mr. Robertson, Mr. Jackson, and Mr. Plton. Mr. Barclay Thompson will lecture on the Anatomy of the Amphibia, at the Museum. At Christchurch Mr. Vernon Harcourt will give a course of lectures on the Elements of Chen stry, and Mr. R. E. Baynes will give a course on Mechanics.

At Magdalen College Laboratory Dr. Pike will lectu e on Chemistry, and Mr. Yule and Mr. Chapman on Biology.

Exeter College has lost the valuable services of Prof. Lankester. Mr. Lewis Morgan, formerly house surgeon at the Radcliffe Infirmary, will carry on instruction in the biological laboratory of the College.

College to a scholarship on the foundation of Miss Hannah Brakenbury, "For the Encouragement of the Study of Natural Science," worth 80/, a year (557. and tuition free), tenable during residence for four years. There is no limit of age, bur members of the University must not have exceeded eight terms from

In the month of November there will be an election at Balliol

IN

THURSDAY, OCTOBER 23, 1879

THE INTRA-MERCURIAL PLANET QUESTION N No. 2253-54 of the Astronomische Nachrichten, Dr. C. H. F. Peters, the discoverer of so many minor planets, has "Some critical remarks on so-called intraMercurial planet observations," including the observations reported by Prof. Watson during the totality of the eclipse of July 29, 1878. Replies to these remarks have since appeared from Prof. Watson and also from Mr. Lewis Swift, of Rochester, New York, who, it will be remembered, also considered he had seen an object which could be no known star or planet. Prof. Peters enters upon other cases where intra-Mercurial bodies have been suspected, but we shall confine ourselves mainly here to his criticism of Prof. Watson's observations during the last eclipse. His object is to adduce evidence disproving Watson's conclusion that he had seen one, probably two unknown planets, and he grounds his argument chiefly upon the small size of the circles to which Watson trusted, and the fact that nearly on the parallel of his two objects a and b, and at an almost equal distance, a small one, in right ascension, were the stars and Cancri. He states that the circles of wood with paper scales pasted on them, were only 5 and 4 inches respectively in diameter, and as Prof. Watson estimated the probable error of a position given by them at only five minutes, the space would measure on the circles only of an inch, and further he states that the wires which served as pointers "were so elastic as easily to give way several degrees under the touch by a pencil." So far, therefore, from accepting Watson's estimate of the precision of his readings, Prof. Peters thinks he does him no injustice in supposing that they were made "at the utmost to inch, corresponding to twenty minutes of arc upon his circles;" and in this case, the differences of a from 0 Cancri, and of from Cancri, or + 2m. 55s. and + 3m. 235. respectively, he believes may be explained by the errors in the markings or readings. It is also urged that the markings for the sun were made under circumstances less hurried than those for the suspected planets. Watson estimated the objects at the time of 4 and 4 magnitude, and, remarking that absolute magnitude must be quite uncertain under such conditions, Peters points out that the difference of brightness corresponds pretty nearly with that given by Argelander, Heis, and others between and Cancri; and he adds, "it is, therefore, quite apparent to every unbiassed mind that Watson observed and Cancri, nothing else." It should be added that Prof. Peters attempts to explain the ruddiness of the object near 0,-"If the sand ledge, under the lee of which the telescope was standing had nothing to do with it; " the observation, perhaps, teaches that the corona possesses the property of less absorbing the red rays, and may, therefore, be of some value. It seems also, in his view, that the corona gives a disk to the stars, or calms down the radiations to a kind of spurious disk, as a slight fog does; and as he does not admit that the power employed would show a real disk, we are to assume this was the case during Prof. Watson's observations. With regard to Mr. Swift's observations, it is represented that his successive publiVOL. XX.-No. 521

cations offer so singular a gradation in the statements as to unfit them to be the subject of a scientific discussion. As we have stated, Prof. Watson has replied to the criticisms which the Clinton astronomer has published to "make evident beyond cavil how erroneous the conclusion too rashly rushed at by the observers." He protests against mis-statement of the facts connected with his observations, remarking that it appears to him the grossest of unfairness to attempt to discredit an observation made by an experienced observer by deliberately misrepresenting the circumstances of the observations." So far from the pointers of his circles bending under the touch by a pencil, they were made of unannealed brass wire one-eighth of an inch in thickness, not filed to a point, but to a knife-edge, placed vertical to the plane of the circle; they were quite rigid, and could not be disturbed in the least by the pencil when marking. The probable errors attributed to his readings Watson declares to be absurd, and says that any one interested may, by a few trials ascertain that by the method he adopted it is possible to measure without a greater probable error than 2'; the limit of 5' which he gave was an outside one. Peters had urged that a practised observer would have compared the object a directly with 0 Cancri, as the two would have been in the field together with the telescope employed, to which Prof. Watson replies, and with justice, that besides the want of time for such direct comparison, the method he was applying was different. If he had known that a new star would present itself near Cancri, he could have prepared himself for direct comparison; under the circumstances his plan of securing rapid indication of the position of any object that might be visible seems to have been as effective a one as could have been devised, and, as Dr. Draper termed it when it was explained to him the night before the eclipse, "a good dodge." Further, Watson observes that the assertion that his circles "were of wood, with paper scales pasted on to them, and wires serving as pointers," shows conclusively that Peters either did not yet understand his method, or that he was "purposely mis-stating the circumstances of his observations."

Finally, he makes what he terms these emphatic declarations :-"I. I observed, during the total eclipse of July 29, 1878, a new star between Cancri and the sun, and south of the sun, whose position and magnitude were as already published by me. 2. I observed another star, which I believe to be a new star, whose magnitude and position were as already published by me." Whether or not these objects were intra-Mercurial planets he does not positively assert, but he had the right to express the hones belief that they were. Watson adds that he "hopes ere long to give good reason for the faith that is in him," by which we understand him to imply that he has the intention to enter further upon the subject.

We will venture to say that the general feeling amongst astronomers when first reading Prof. Watson's announcement of his observations during the totality of the eclipse of 1878, of one, if not two, unknown objects, would be that a man of such known ability and experience as an observer, and so good a practical astronomer, as shown, amongst other proofs, by his able treatise on practical astronomy, would not risk his whole scientific reputation by putting forth such a statement to the world, unless he

D D