434 absorbed aqueous vapor, and this absorption, which is explained by the hygrometric property of the glycerine, had continually repaired the diminution of thickness due to the descent of the liquid. Now, in the present experiment, as there was no water in the jar, and hence the atmosphere which surrounded the bubble was less humid, it might be supposed that the effect of the descent of the liquid had at first prevailed over that of the absorption, and that afterwards it was the contrary which took place. Upon this assumption, I deposited in the bottom of the dry jar morsels of caustic potash, and contrived by the application of a little lard around the orifice of the jar and of the aperture through which passed the copper tube, that, after the introduction of the bubble, the pasteboard disk should close the opening hermetically. Further, as the small quantity of liquid which always accumulates by degrees at the base of the bubble must contribute by its weight to cause a rupture of the latter, a space of ten minutes was allowed to elapse before the removal of the drop; the film had thus already become thinner when it was introduced into the jar, and the accumulation resulting from the further descent of the liquid would be much less. Now, under these conditions, the diminution of thickness of the film was continuous, the bubble lasted for nearly three days, and when it burst, it had arrived at the transition from the yellow to the white of the first order; it then presented a central space of a pale yellow tint, surrounded by a white ring. The level of the water in the observed branch of the manometer underwent small oscillations, sometimes in one direction, sometimes in the other, but the last of them was in the direction of an augmentation of pressure. Although, during the long duration of this bubble, the temperature of the apartment had necessarily undergone slight changes, the oscillations just mentioned could not be entirely attributed to these, for, if that had been so, there would have been seen, after each of the three nights, a movement of the manometer in the direction of an augmentation of pressure; but the contrary was observed after the first two nights, and it was only after the third that there was a movement in that direction. From the progression of these movements it results that if the pressure varied, it was in an irregular manner, in both directions, and terminating not in a diminution, but an augmentation at least relative; we may therefore admit, I think, that the final thickness of the film was still superior to double the radius of sensible activity of the molecular attraction. 1 8554 § 33. Let us now see what we may deduce from this last experiment. According to the table given by Newton, the thickness of a film of pure water which reflects the yellow of the first order is, in millionths of an English inch,. 5, or 5.333, and for the white of the same order 37, or 3.875. We may therefore take the mean, namely 4.064, as the closely approximative value of the thickness corresponding, at least in the case of pure water, to the transition between those colors and the English inch being equal to 25mm.4, this thickness is equivalent to of a millimetre. Now we know that, for two different substances, the thickness of the films which reflect the same tint is in the inverse ratio of the indices of refraction of those substances. In order therefore to obtain the real thickness of our film of glyceric liquid, it suffices to multiply the denominator of the preceding fraction by the ratio of the index of the glyceric liquid to that of water. I have measured the former approximately by means of a hollow prism a liquides, and have found it equal to 1.377. That of water being 1.336, there results, for the thickness of the glyceric film, of a millimetre. The half of this quantity, or of a millimetre, constitutes therefore the limit furnished by the experiment in question. Hence we arrive at the very probable conclusion, that in the glyceric liquid the radius of sensible activity of the molecular attraction is less than 17000 of a millimetre. 17622 I had proposed to continue this investigation with a view to reach, if possible, the black tint, and to elucidate the variations of the manometer; but the cold season has intervened, diminishing the persistence of the bubbles, and I have been forced to postpone my attempts till a more favorable period. Note on the preparation of the glyceric liquid with the impure glycerines of commerce. The first glycerine which I tried was that sold by the apothecaries of Ghent. It is of an intense yellow color and disagreeable odor, and contains in large quantity a foreign substance, which I believe to be lime, and of which it is necessary to rid it. After many fruitless attempts, the following process occurred to me, and has been attended with considerable success: Mix in a flask a suitable quantity of distilled water and an equal quantity of the glycerine in question; then introduce into the flask a quantity of Marseilles soap cut in thin shavings, whose weight should be about a fifteenth of that of the water; these shavings remain floating on the liquid. The soap should have been kept in a moist place; if dry, the action is scarcely appreciable. After five minutes the flask is to be slowly turned three or four times, when small white particles will be seen to be detached from the soap and disseminated through the liquid, and which, when the flask is left at rest, gradually ascend. The slow turning is to be repeated at intervals of five minutes, for an hour and a half; the particles become more and more numerous, and eventually and permanently fill the whole mass. The greater part of the soap remains unattacked, but an excess was needed in order to present the more surface to the action of the liquid. This is disengaged from the particles and the excess of soap by passing it through a filter formed of cotton stuff of close texture; when a new supply of the soapshavings equal to the first is introduced, and the turnings are to be repeated as before for the space of an hour, the particles again form and must be separated anew by filtering; the liquor now passes in a milky state, but is rendered lim pid, or nearly so, by filtering it through paper; the preparation is then complete. All these operations should be conducted at a time when the outer temperature and that of the apartment are from 18° to 20°; if this last limit be greatly exceeded the liquid will dissolve too much soap. A bubble formed of this liquid and deposited on a ring, as indicated in §§ 13 and 15, may subsist for perhaps an hour and a half. This liquid, however, has one serious inconvenience; at a temperature below 18° it fails altogether to yield bubbles; hence, when we wish to use it in winter, it is necessary previously to keep the flask for about an hour in water maintained at 20°. It is needless to add that the apartment should be warmed. I have tried, in the second place, a glycerine which came, as I was assured, from Paris. It has the same color and the same odor with that from Ghent. When mixed with the solution of soap the compound is at first slightly turbid, and after some hours becomes very milky. If this liquid be left at rest the precipitate, as in the case of the glycerine of London, already described, ascends gradually, and forms in a few days a distinct layer on the top. Here, also, the limpid liquid should be withdrawn by means of a siphon. The proportions which I have used with most success are five volumes of glycerine and four of the same solution of soap employed for the glycerine of London. The liquid thus obtained yielded bubbles which lasted five quarters of an hour. This trial was made in autumn, at a time when the external temperature did not rise above 7° or 8°, by operating in a warmed apartment, but without any other precaution. It is probable that the same liquid prepared in summer would furnish films of a still greater persistence. I am led to believe, from what I know of the different processes by which the glycerines of commerce are obtained, that all that can be procured are analogous to one or other of the three which I have employed; hence it will be seen that the best course is to obtain the substance from London, provided none as pure can be found elsewhere. OUTLINE OF A SYSTEMATIC REVIEW OF THE CLASS OF BIRDS. BY PROFESSOR W. LILLJEBORG, OF UPSALA. [From proceedings of Zoological Society of London, for January, 1866.] [The following article is believed to present the later views of some of the best systematic ornithologists in reference to the classification and arrangement of the higher divisions of birds, such as have been adopted in the main by the highest authorities. It is essentially the same as has been followed in the recent rearrangement of the mounted birds in the museum of the Smithsonian Institution. The article, as written in the original Swedish, was translated some years ago by Professor Jillson, then of the United States Patent Office, for publication in the annual report of the Institution, but the MSS. was mislaid in the hands of a gentleman to whom it was intrusted for the purpose of revision, and never found. The present paper is of later date, and presented in an English dress to the Zoological Society of London, early in 1866, by the author. The tables, originally in Latin in this communication, have been translated into English by Professor Gill.-J. HENRY. J LITERATURE. We may particularly mention Chr. L. Nitzsch,* C. J. Sundevall,† G. R. Gray, J. Cabanis,§ and C. L. Bonaparte,|| among those that of late years have devoted their attention to the classification of birds. John Müller ¶ has given an important contribution to this classification by his treatise on the apparatus of singing in the larynx inferior in a great number of Passeres. The contribution given by Nitzsch certainly contains only a very short and incomplete review of the class of birds; but it has, notwithstanding, a particular scientific value from its attracting attention to the importance that the carotides communes of the birds have in their classification. The ornithological system given by Sundevall has the merit of being based upon a careful and particular examination of the exterior characters of the birds, and of, for the first time, calling attention to the importance of the wingcoverts in classification, and exhibits a correct idea of the designating characters in the nature of the birds. The structure of the wings generally has been minutely described in the treatise on these organs, and its importance as regards * Observationes de Avium arteria carotide communi. Hala, 1829. (Appendix to a programme by Prosector Fridericus Blumius Ictus.) + Ornithologiskt system (Transactions of the Royal Academy of Science of Sweden, for the year 1835, (printed 1836,) p. 43.) Over foglarnas wingar (ibid. for the year 1843, (printed 1844,) p. 303.) Svenska foglarna, 1856. A List of the Genera of Birds, (London, 1841.) The Genera of Birds, (London, 1844–49.) Ornithologische Notizen (Wiegmann's Archiv für Naturgeschichte, 1847, vol. i, pp. 186 and 308.) Museum Heineanum, (Halberstadt, 1850-63.) Conspectus generum avium (Leyden, 1850-57;) Conspectus systematis ornithologiæ (Annales des Scienco Naturelles, 1857? ;) Tableaux paralléliques des ordres Linnéens, Anseres, Grallæ, et Grallinæ, (Paris, 1856.) (Extract from Comptes Rendus des Séances de l'Académie des Sciences;) besides several other treatises in different magazines. ¶ Abhandlungen der königl. Akad. der Wissenschaften zu Berlin, 1847, p. 321. classification held forth. As the wings must be considered to be of the highest importance to a bird, being among those parts that indeed make him a bird, it is natural that a system in which the structure of the wings has been considered should be preferable to any other where the wings have been neglected, or this subject but slightly touched upon, without any minute examination of their structure. The above-mentioned author has, in his "Svenska Foglarna,” observed the muscular structure of their feet as important in classification, after having previously, for the first time, called attention to the same at the meeting of naturalists in Stockholm, in 1851. The new genera and species that have been added since Latham's "Index Ornithologicus" was edited had increased to such a number, and their literature had become so scattered, that such a work as G. R. Gray's systematic "List of the Genera of Birds," although only a list of names without characters, was very necessary to science, and the obtaining of the same also highly beneficial. The right of priority has generally been observed in this work. The same author has, in his "Genera of Birds," given descriptions of the orders, families, and genera, and even figures of the same. A single species of some genera is represented by a colored figure; and of others only certain parts, such as the head or the foot of some typical species, have been figured. This work is certainly of great value for the study of birds; and the very good figures often give a necessary explanation to the descriptions of the genera, which at times are but little distinguishable, and are not given in a diagnostic manner. Cabanis has, in his ornithological system, given good characters for the arranged groups, taken partly from J. Müller's descriptions of the inferior larynx, partly from the nature of the horny covering on the tarsi, first studied by Keyersling and Blasius, and partly from the number of quills and tail-feathers. It is principally the order Passeres to which this author has devoted his attention, and which consequently has obtained an improved classification. It has been divided into two groups, (Oscines and Clamatores,) and the families have been carefully limited and arranged. This work, with that of Sundevall, may rightly be considered most important in the classification of birds. The numerous contributions to this classification that have been made by Bonaparte are valuable as giving minute registers of families and species, showing an unusual knowledge of the species, and a sharp distinction between the genera, and often arranging these in a manner corresponding with the demands of the natural affinity; but they are generally only registers of names, often giving the characters for the species, but very seldom for the higher groups. Bonaparte has published, in the "Transactions of the Linnean Society," xviii, p. 258, a systematic arrangement of the class of birds, together with the classes of the other vertebrated animals in general. The first class has been divided into two sub-classes-Insessores and Grallatores. The first of these corresponds fully with the one arranged by us under the same name, and the latter includes both Gralle and Natatores. This classification corresponds also with the one given here, in the Longipennes having their place between the Steganopodes and the Pygopodes. Characters of the orders, families, and subfamilies are also given. After this brief reference to the literature, we will proceed to a synoptic statement of the principles upon which the systematic arrangement here given rests. PRINCIPLES. We have preferred the progressive method, as it seems to us to be the most rational, from its correspondence with the physiological and geological development. We therefore commence the system with the lowest, and finish it with the highest forms. Irritability seems to us to be the most distinguishing character for birds; and this should consequently be taken into consideration more than others with regard to their classification. The swimmers seem to us the lowest, from their showing a tendency to the lowest form of vertebrated animals-the fish form. In the Aptenodytide, where the wings resemble fins, and where they, as in all other diving birds, serve as such, we have this form most strongly designated. The heavy, clumsy structure, with small wings and short legs, also makes them generally less active than other birds, and shows a lower development of the type of bird. This, however, is not the case with all the swimmers; and the order Longipennes gives us instances where swimmers possess a high degree of activity. The Passerine birds (Passeres) seem to us to possess the highest irritability, and to be those in which the nature of birds has reached its highest development. We do not by irritability mean the muscular strength alone, but vivacity and activity generally. Where this is most manifold, most changing and constant, it is the most developed. We find in the Passeres "the power to stay and move with ease as well on the ground as in the trees or in the air, and to make their presence known by characteristic melodious notes," (Sundevall;) we find them in a constant and manifold motion, and they let us constantly hear their notes either as song or as affectionate voices. The birds of prey have generally been placed highest, and been considered the most developed, in consequence of their muscular strength and strong flight, and their thereby supposed high degree of irritability; but by keeping them in captivity we find at once that the birds of prey are dull birds, and that they, as regards irritability, are far behind the Passeres. They remain for a long time silent and quiet, and do not generally show any activity, unless they are frightened or driven by appetite for food. The Passerine birds, on the contrary, are in captivity constantly in motion, and let us incessantly hear their lively song and affectionate voices. Besides, we cannot in a system place the birds of prey far from the lower groups of the Columbine and the Gallinaceous sections without violating natural affinities based upon important characters. They correspond with these lower groups as regards external characters in the nature of their wing-coverts, and, as regards interior anatomical characters, in the nature of their carotides communes. Some of them, for instance those of the Vulturine section, exhibit, with regard to their form, a near analogy with some of those of the two mentioned groups. We may, for instance, compare a Condor with a Turkey. A system that places the dirty Vultures highest does not seem to us to indicate a correct idea of the nature of the birds. If we do not regard flight, which is common to almost all birds, but consider birds with regard to the various other ways of motion for which they especially are shaped, and for which their structure is also adapted, we find easily that these in general may be comprehended in three different modes, viz: 1st, swimming on the water; 2d, running on the ground; and 3d, climbing and jumping on the branches of trees.* The hinder extremities or the legs exhibit, in conformity with this, three different forms. This induces us to divide the class of birds into three primary groups or sub-classes: 1, Natatores; 2, Cursores; 3, Insessores. Those belonging to the third group generally move more with the assistance of their wings than the others, except some forms of the Natatores, and show generally a higher development of the bird-type. This group also furnishes the greatest variety of forms. The Natatores include about 550 species, the Cursores 900, and the Insessores 6,900, (Bonaparte.) Nitzsch has, in the treatise referred to, divided the class of birds into three groups: Aves aëreæ, Aves terrestres, and Aves aquaticæ, which in a reverse order correspond with the three groups here arranged; but he differs from us in including the Columbine birds among the Terrestres, and the Grallatorial birds *The second mode appears an intermediate link between the first and third. |