anatomy without the shelter of a quill. Plumage indeed of every kind is non-resistent to Röntgen's rays; and that the skin of a fish is scarcely less transparent than the element in which it moves, will be seen at a glance by our readers. It was taken by Mr. A. A. Campbell Swinton with a focustube' invented at King's College, by means of which the shadows thrown on the sensitive plates gain greatly in sharpness. The companion-pictures are likewise specimens of his best work; and they have been admirably reproduced by the Swan Electric Engraving Company. The embryonic character of the skeleton of the two days' old puppy-dog will be noticed; also the poor frog's broken leg, the discomfort attendant on which must have considerably detracted from the marshy joys' of his life. The spine and ankle are masterpieces; the dissecting faculty of the X-rays could not be more perfectly displayed; and the pair of spectacles, in its shagreen case, illustrates both the extraordinary permeability by them of animal-hides, and the marked difference in opacity between steel and glass. Among other curiosities of portraiture, we hear of pigeons and sparrows, mice and rabbits, anatomised in despite of fur and feathers; and of a crayfish, taken by Mr. W. A. D. Rudge, the shell of which proved to be of about the transparency of aluminium. The surgical uses of Professor Röntgen's marvellous discovery are innumerable; and fresh instances of its successful application furnish themes for weekly comment in the Lancet' and other specialist papers. The veil of flesh may now at will be withdrawn from the bony structure beneath, the diseases and malformations of which can be studied in autographic representations. Calcareous deposits in the various organs of the body, ossifications, intruded foreign substances, stand out in relief, indicating with certainty the seat of disorder, guiding the hand of the operator, and rendering exploratory processes superfluous. Suitable patients are at a premium. A woman who has absorbed a needle, a man harbouring a projectile, is a persona grata at every Surgical Institute in the Old and New Worlds. Had Aspromonte been fought in these tempi leggiadri, Garibaldi's ankle would have been quit of its bullet in fewer hours than the weeks of its actual lodgment. The profit derivable to medical diagnosis from the novel method, although less direct and immediate than its surgical utility, is sure before long to accrue. But the delicate modifications of exposure and development, by means of which the internal organs will be brought, it is hoped, within the range of radiographic inspection, must be worked out tentatively, by the the aid of instruction from daily experience. An important step has, however, already been taken by the substitution, to a certain limited extent, of the human retina for the sensitive plate. Professor Salvioni's 'cryptoscope,' described before the Medico-Chirurgical Academy of Bologna, February 6, 1896, consists of a tube, completely closed at one end by a disc of black cardboard overlaid with fluorescent sulphide of calcium, for which Edison substitutes the tungstate of the same metal. Under the influence of the X-rays, the diaphragm thus prepared becomes brilliantly luminous, and the shadows of interposed objects, more or less dense according to the degree of their transparency, are readily seen by an eye applied to the open end of the observing cylinder. We can, in this way, count at a glance the bones in our own hand, or inspect the contents of our neighbour's pocket. Hence instant discernment of the invisible' must henceforth be reckoned among the resources of civilization. So handy an instrument for examining the interior of the body must, before long, find its way into the hands of every physician. Nor is it impossible that, by its employment, much information may be gathered regarding the nature of vital processes. The circulation of the blood may be watched, the throbbings of the heart, the progress of digestion, the elaboration of secretions. Even a bony rampart will not perhaps avail to protect from scrutiny the organs behind it. For M. Charles Henry has discovered that a coating of sulphide of zinc diminishes or abolishes opacity to Röntgen's rays; and he hazards the forecast that, by painting the breastbone with this fluorescent salt, a view right through it of the heart and lungs may be afforded. Nor do we dare to pronounce him over-sanguine. The practical performances of radiography warrant high hopes for its future. M. Brouardel of Paris has induced it to display the contents of infernal machines; volumes innocent of aspect have in the same way been shown by MM. Girard and Bordas to be crammed with explosives and projectiles; and thus, the peril of forcing open suspicious parcels can be evaded by merely exposing them to emissions from a vacuum-bulb. The similar detection of flaws in pieces of metal promises to afford a safeguard against accidents to machinery, or with ordnance; † a great advance in dentistry, through the same agency, is announced as imminent; and it supplies an easy and unfailing test for the genuineness of diamonds. But the versatility of its powers can hardly yet be appreciated. Comptes Rendus,' Feb. 10, 1896. Nature,' Feb. 21, 1896. The easy passage of the new rays through carbon and its compounds with oxygen, hydrogen, and nitrogen, is the particular faculty by which they have gained their sudden fame; since it is that to which is due the astonishing transparency to them of all bodies of organic origin. They traverse pineboards hardly enfeebled; almost disregard ebonite, vulcanite, gelatine, leather, jet; and run through printed matter with a facility unknown to the most indolent reviewer, producing their characteristic effects, fluorescent and photographic, after a journey through a book of a thousand pages. Hence a sixpence placed in the midst of a bulky tome becomes fully apparent as an obstacle to their transit. And the heavier the metal, the more conspicuous its interposition. Professor Dewar has in fact ascertained that these gradations of transparency are regulated by atomic weights. The complexity of the molecule is of no consequence in this respect; only the mass of the individual atom tells. Electrical or optical properties, colour, crystalline structure, chemical combinations, count for little or nothing; the atomic principle is dominant throughout. Here we have one of many symptoms that the rays concern themselves with matter only in its finest subdivisions, ignoring it as an extended mass. It should be added that they suffer no deflection in a magnetic field. What then are these singular einanations? Their indifference to the magnet shows decisively that they are not streams of electrified particles, like the cathode-rays. They may accordingly be set down with confidence as a mode of ethereal vibration. The question inevitably follows: Should they be regarded as a peculiar kind of invisible light'? The title is no longer paradoxical; for the scientific meaning of the word 'light' has of late incalculably widened. Clerk Maxwell's electro-magnetic theory of light, splendidly verified by Hertz, lends coherence and unity to ideas concerning the energies of the material universe. For we now know that the 'luminiferous ether' is possessed of far more versatile powers than that phrase imports. It transmits electrical oscillations some miles long, ultra-violet wavelets, more than 120,000 of which are crowded into a single inch, together with endless intermediate undulations, a small fraction of which serve us for purposes of vision. Yet all belong to the same grand series. They travel with an identical speed of 186,000 miles a second; they obey the same laws of reflection, refraction, and polarisation; all can be extinguished by interference; and all are therefore to be regarded as disturbances of one medium differing only in scale and period. Like the waves of the sea, these various oscilla |