Chapter 9

"Alongside of these general infective diseases produced by bacilli, local affections also occur, which indicate the presence of these organisms at the point where disease begins. As an example of these processes, which probably occur in various organs, I would mention gastritis bacillaris, of which I shall show you preparations. In this, we can trace the entrance of the bacilli into the peptic glands, as well as their further distribution in the walls of the stomach, and in the vascular system.

"The second group of the pathogenetic schizomycetae I propose to call, with Billroth, cocco-bacteria, because they consist of collections of micrococci, which are capable of transforming themselves into short rods. The former usually form groups united by zoögloea; by prolongation of the cocci rods are formed, which sprout out, break up by division into chains, and further lead again to the formation of resting masses of cocci. I distinguish, further, in this group, two genera--the microsporina and the monadina; in the former of which the micrococci are collected into spherical lumps, in the latter into layers. The one class is developed in artificial cultivation fluid, the other on the surface. The former requires a medium poor in oxygen, the latter a medium rich in oxygen, for their development.

"Among the affections produced by microsporina, I reckon especially the septic processes, and also true diphtheria. On the other hand, to the processes produced by monadina belong especially a large series of diseases, which according to their clinical and anatomical features, may be characterized as inflammatory processes, acute exanthemata, and infective tumors, or leucocytoses. Of inflammatory processes, those belong here which do not generally lead to suppuration, such as rheumatic affections, including the heart, kidney, and liver affections, which accompany this process, sequelae which, as is well known, lead more especially to formation of connective tissue, and not to suppuration. Here, also, belong croupous pneumonia, the allied disease erysipelas, certain puerperal processes, and finally, parotitis epidemica, or mumps.

"Among the acute exanthemata, the following may, up to the present time, be placed in this group; variola-vaccina, scarlatina, and measles.

"The group of infective tumors is represented by tuberculosis, syphilis, and glanders. Throughout the whole group of cocco-bacteria the demonstration of organisms in the diseased parts encounters difficulties which vary considerably in the different kinds."

The speaker concluded by describing the methods (now well known) by which the powers of the different organisms are tested.

He also referred to Pasteur's, Chauveau's, and Toussaint's recent experiments.

His conclusion was that the specific communicable diseases are produced by specific organisms.

* * * * *

THE CENTENARY OF THE DISCOVERY OF URANUS.

By W. F. DENNING, F.R.A.S.

The year 1781 was signalized by an astronomical discovery of great importance, and one which marked the epoch as memorable in the annals of science. A musician at Bath, William Herschel by name, who had been constructing some excellent telescopes and making a systematic survey of the heavens, observed an object on the night of March 13 of that year, which ultimately proved to be a large planet revolving in an orbit exterior to that of Saturn. The discovery was as unique as it was significant. Only five planets, in addition to the Earth, had hitherto been known; they were observed by the ancients, and by each succeeding generation, but now a new light burst upon men. The genius of Herschel had singled out from the host of stars which his telescope revealed an object the true character of which had evaded human perception for thousands of years!

The centenary of this remarkable advance in knowledge naturally recalls to mind the circumstances of the discovery, and makes us inquisitive to know what new facts have been gleaned of Herschel's planet, now that a hundred years have passed away, and we are enabled to look back and review the vast amount of labor which has been accomplished in this wide and attractive field of astronomical research. We may learn what new features have been discerned of the new body, and what additional discoveries in connection with other planets unknown in Herschel's day, have been effected by aid of the powerful telescopes which have been devoted to the work. We do not, however, intend dealing with the general question of planetary discovery, for at a glance we are impressed with its magnitude. While a century ago five planets only were known, we now have some two hundred and thirty of these bodies, and the stream of discovery flows on without abatement through each succeeding year. The detection of Uranus seems, indeed, to have been the prelude to many similar discoveries, and to have offered the incentive to greater diligence and energy on the part of observers in various parts of the world.

Many great discoveries have resulted from accident; and the leading facts attending that of Uranus prove that, in a large measure, the result was brought about in a similar way. Herschel, as he unwearyingly swept the heavens night after night, was in quest of sidereal wonders--such as double stars and nebulae--and he happened to alight upon the new planet in a purely chance way. He had no expectation of finding such a remarkable object, and indeed, when he had found it, wholly mistook its character. There could be no doubt that it was a body wholly dissimilar to the fixed stars, and it was equally certain that it could not be a nebula. It had a perceptible disk, for when it had first come under the critical eye of its discoverer he had noticed immediately that its appearance differed widely from the multitude of objects which crossed the field of his telescope. He had been accustomed to see hosts of stars pass in review, and their aspect was in one respect similar, namely, they were invariably presented as points of light incapable of being sensibly magnified, even with the highest powers. True, there was a great variety of apparent brightness in these objects and a singular diversity of configuration, but there was no exception to the invariable feature referred to. The point of light was constant, and no striking exception was anticipated until one night--March 13, 1781--Herschel being intently engaged in the examination of some small stars in the region of Gemini, brought an object under the range of, his telescope, which his eye at once selected as one of anomalous character.

Applying a higher power, he noticed that it exhibited a planetary disk, but his instrument failed to define it with sufficient distinctness, and hence he became doubtful as to its real nature. The object was found to be in motion, and subsequent observations led him to the assumption that it must be a comet of rather exceptional type. This appeared to be the best explanation of the strange body, for history contained many records of curious comets, some of which were observed as nearly circular patches of nebulous light, and probably of similar aspect to the object then visible; and apart from this it must be remembered that the idea of a large planet exterior to Saturn was a fact of such momentous import that Herschel, with a due regard to that modesty which accompanies true genius, refrained from attaching such an interpretation to his observations. He was content to direct the notice of astronomers to it as a phenomenon requiring close attention, and suggested that it might be a comet in consequence of its motion and the faint and somewhat ill-defined character of its appearance.

From the earliest ages five planets only were known, and the discovery of another large planet beyond the sphere of Saturn must at once revolutionize existing ideas as to the range of the solar system, and immediately take rank as a scientific event of equal interest to the discovery of the moons of Jupiter or the rings of Saturn, which each in their day impressed men with new ideas of the celestial mechanism. But the truth could not long be delayed. The new body being watched and its orbit rigorously computed from a series of observed positions revealed its true character, and Herschel was awarded the honor due to the author of a discovery of such importance. His diligence and pertinacity alone had enabled him to search out from among the multitude of stars thickly strewn over the firmament this unknown and well-nigh invisible planet which, during all the preceding years of the world's history, had eluded human perception. Men had been all unconscious of its existence as it had been slowly completing its circuits around the sun, obedient to the same laws as the other planets of the solar system, and awaiting the hour when the unfailing eve of Herschel should introduce it as the faint and far-off planet girding our system within its expansive folds.

As soon as the existence of the new orb was confirmed and the fact rendered indisputable, the question naturally arose whether it had ever been seen in former years by the authors of star catalogues, who could hardly have overlooked an object like this though its planetary nature had manifestly escaped detection. It was just perceptible to the naked eye, shining like a star of the sixth magnitude, and ought to have been distinguished by those who had reviewed the heavens with the purpose of determining and mapping the positions of the stars. Reference was, therefore, made to the chief catalogues, when it was found at once that the planet had been unquestionably observed by Tobias Mayer, Le Monnier, Bradley, and Flamsteed. It was several times noted by these observers: by Le Monnier no less than twelve times, and by Flamsteed on six occasions; and it is remarkable that in every instance its true character escaped detection. Neither its special appearance nor its motion attracted attention, so that it was merely catalogued as an ordinary fixed star. Thus Herschel was not anticipated in his discovery. It remained for him, in 1781, to note its exceptional aspect, and to specify it as an object requiring critical investigation. But the early observations above alluded to served a useful purpose in testing the accuracy of the computed orbit, for without waiting many years to compare the theoretical and observed positions, astronomers had in these old records a reliable series of points through which the previous course of the planet could be traced.

The calculations showed that its mean distance from the sun was some 1,750,000,000 miles, and that a revolution was completed in about eighty-four years. It was also found to be a very large planet, greatly exceeding either Mercury, Venus, the Earth, or Mars, though considerably inferior to either Jupiter or Saturn.

Here, then, was a discovery of the utmost importance, and one of the most salient additions to our knowledge which the telescope had ever achieved. The new planet was now definitely assigned its proper place in the solar system, and was regarded as of equal significance with the old planets. True, the new planet of Herschel could not be compared as regards its visible aspect with the other previously known members of our system, but it was nevertheless an object of equal weight. Its vast distance alone rendered it faint. It formed one of the constituent parts of the solar system, which, though separated by immense intervals of space, are yet coherent by the far-reaching effects of gravitation. There is, indeed, a bond of harmony between the series of planetary orbits, which exhibit a marked degree of regularity in their successive distances from the sun; and though they are not connected by any visible links, they are firmly held together by unseen influences, and their motions are subject to certain laws which have been revealed by centuries of observation.

The question of suitably naming the new planet soon came to the fore. Herschel himself proposed to designate it the "Georgium Sidus," in honor of his patron, George III., just as Galileo had called the satellites of Jupiter the "Medicean stars," after Cosmo de' Medici. But La Place proposed that the planet should be named after its discoverer; and thus it was frequently referred to as "Herschel," and sometimes as "The Herschelian planet." Astronomers on the continent objected to this system of personal nomenclature, and argued that the new body should receive an appellative in accordance with those adopted for the old planets, which had been selected from the heathen mythology. Several names were suggested as suitable (on the basis of this principle), and ultimately the one advanced by Bode received the most favor, and the planet thereafter was called "Uranus."

The varying positions of the new body as observed on successive nights were determined by comparisons with a group of six small stars, termed by Herschel [Greek: alpha, beta, gamma, delta, epsilon] and afterwards formed into a constellation under the designation of "Britannia," though it does not appear that this little asterism is acknowledged as one of our constellations. Its position is about midway between Taurus and Gemini, and the following are the principal stars computed for 1881.0, as given by Mr. Marth:

Star. Magnitude. Right Ascension. Declination. h. m. s. alpha 9.0 5 42 6.06 23° 35' 6.7" N. eta 8.7 5 43 17.82 23 26' 7.2 N. theta 8.8 5 44 0.99 23 53' 30.8 N. epsilon 8.8 5 45 40.68 23 34' 46.8 N.

The stars are therefore merely telescopic, and are confined to a small area of space, so that the propriety of adopting the group as a distinct constellation is very questionable. Their positions close to Uranus at the time of its discovery, and the fact that the planet's motion was detected by means of comparisons with them, has given to these stars an historical interest which in future years must often attract the student to their reobservation. But it would be unwise, as forming a bad precedent, to accept a group of stars of this inferior type as meriting to rank among the old constellations, when we have numbers of richer groups, situated on their confines, which first deserve such a distinction. However special or unique the circumstances connected with certain telescopic stars may be, and however necessary it may appear to signalize them by a specific title, we are inclined to question the adoption of such means as likely to exercise a wrong influence, inasmuch as it may hereafter originate further innovations of a similar character, and ultimate complications will be certain to arise.

Soon after the discovery of Uranus it was suspected that the planet was encircled, like Saturn, by a luminous ring, but on subsequent observation this was not confirmed, and no such appendage has ever been revealed in the more perfected instruments of our own times. Indeed, if Uranus displays a peculiarity of constitution in any way analogous to the ring system of Saturn, it must be of the most minute character so as to have thus evaded telescopic scrutiny during a hundred years.

The discovery soon attracted the notice of royalty, and the reigning sovereign, George III., anxious to practically express his appreciation of the valuable labors of Herschel, awarded him a pension of £200 a year and furnished him with a residence at Slough, near Windsor, and the means to erect a gigantic telescope with which he might be enabled to continue his important researches. This instrument consisted of a reflector on the "Front-view" construction, with a speculum 4 feet in diameter and of 40 feet focal length. Upon its completion, Herschel immediately began to observe the region of the new planet with the idea of discovering any satellites which might belong to it, for analogy suggested that it was surrounded by a numerous retinue of such bodies. He was soon successful, for, on the night of January 11, 1787. he saw two minute objects near the planet, which renewed observations revealed to be satellites; and he detected two additional ones in 1790, and two others in 1794, making six in all. But the observations were of extreme difficulty. The path of the planet frequently passed near minute stars, and it became hard to distinguish between them and the suspected satellites. Herschel, however, considered he had obtained conclusive evidence of the existence of six satellites with sidereal periods ranging from 5d. 21h. 25m. to 107d. 16h. 39m., and his means of observation being much superior to those possessed by any of his contemporaries it was impossible to have corroborative testimony.

The matter was thus allowed to rest until the middle of the present century, when Lassell, in the pure sky at Malta, endeavored to reobserve the satellites with a two-foot reflector. This instrument was considered superior to Herschel's telescope; and the atmosphere at this station being decidedly more suitable for such delicate observations than in England, it was removed there for the express purpose of dealing successfully with objects of extreme difficulty. The results were very important. Mr. Lassell became convinced that Uranus had only four satellites, and that if any others existed they remained to be discovered. Two of these were found to be identical with those seen by Herschel in 1787, and now called Titania and Oberon. The other two, Ariel and Umbriel, could not be identified with any of those alleged to have been previously detected by Herschel, so that the inference was that they were new bodies, and that the priority of discovery was due to Mr. Lassell; whence it also followed that the older observations were erroneous, and that in fact Herschel had been entirely mistaken with regard to the four satellites he believed he had detected subsequently to 1787.

In November, 1873, a fine twenty-six-inch object glass, by Alvan Clark, was mounted at the U. S. Naval Observatory at Washington, and it was soon employed upon the difficult task of solving the problem as to the exact periods of the Uranian satellites. This was very satisfactorily effected, and with distinct and conclusive favor to Mr. Lassell, whose observations were fully corroborated. Only four satellites could be distinguished by the American observers, and their periods, as computed from a valuable series of measures, agreed with those previously derived at Malta. In Appendix I. to the "Washington Observations" for 1873, Prof. Newcomb gave a valuable summary of results--the first obtained, be it noted, with that splendid instrument which soon afterward, in 1877, revealed the satellites of Mars--which included the elements of the satellites of Uranus as follows:

Mean Longitude.

Satellite. Epoch 1871. Radius of Period of Dec. 31, W.M.T. Orbit. Revolution in days. I. Ariel........ 21.83° 13.78" 2.52038 II. Umbriel..... 13.52 19.20 4.14418 III. Titania..... 229.93 31.48 7.70590 IV. Oberon...... 154.83 42.10 13.43327

Speaking of the comparative brightness of the satellites, Prof. Newcomb says:

"The greater proximity of the inner satellites to the planet makes it difficult to compare them photometrically with the outer ones, as actual feebleness of light cannot be distinguished from difficulty of seeing arising from the proximity of the planet. However, that Umbriel is intrinsically fainter than Titania is evinced by the fact that, although the least distance of the latter is somewhat less than the greatest distance of the former, there is never any difficulty in seeing it in that position. From their relative aspects in these respective positions I judge Umbriel to be about half as bright as Titania. Ariel must be brighter than Umbriel, because I have never seen the latter unless it was farther from the planet than the former at its maximum distance.... I think I may say with considerable certainty that there is no satellite within 2' of the planet, and outside of Oberon, having one-third the brilliancy of the latter, and therefore that none of Sir William Herschel's supposed outer satellites can have any real existence. The distances of the four known satellites increase in so regular a way that it can hardly be supposed that any others exist between them. Of what may be inside of Ariel it is impossible to speak with certainty, since in the state of atmosphere which prevails during our winter all the satellites named disappear at 10" from the planet."

Prof. Newcomb mentions that no systematic search for new satellites was undertaken because it must have interfered with the fullness and accuracy of the micrometer measures of the old satellites, which constituted the main purpose of the observations. Some faint objects were occasionally glimpsed near the planet, and their relative places determined, but they were never found to accompany Uranus. The fact, therefore, that no additional satellites were discovered is not to be regarded as a strong point in favor of the theory of their non-existence, because the great power and excellence of the telescope was expressly directed to the attainment of other ends; and moreover the season in which the planet came to opposition was distinctly unfavorable for the prosecution of a rigorous search for new satellites. There can, however, be no doubt that the analogies of the planetary systems interior to Uranus plainly suggest that this planet is attended by several satellites which the power of our greatest telescopes has hitherto failed to reveal; and that it is in this direction and that of Neptune we may anticipate further discoveries in future years when the conditions are more auspicious and the work is entered upon with special energy, aided by instruments of even greater capacity than those which have already so far conduced to our knowledge of the heavenly bodies.

Notwithstanding the extreme difficulty with which the Uranian satellites are observed, the two brighter ones, Titania and Oberon, discovered by William Herschel in 1787, have been occasionally detected in telescopes of moderate power, and identified by means of an ephemeris which has shown that the computed positions approximately agree with those observed. During the last few years Mr. Marth has published ephemerides of the satellites of both Saturn and Uranus, and many amateurs have to acknowledge the valuable aid rendered by these tables, which supply a ready means of identifying the satellites, and thus act as an incentive to observers who are induced to pursue such work for the sake of the interesting comparisons to be made afterward. In one exceptional instance the two outer satellites of Uranus appear to have been glimpsed with an object glass of only 43 inches aperture, and the facts are given in detail in the "Monthly Notices of the R.A.S.," April 1876, pp. 294-6. The observations were made in January, February, and March, 1876, by Mr. J.W. Ward, of Belfast; and the positions of the satellites, as he estimated them on several nights, are compared with those computed, the two sets presenting tolerably good agreement. Indeed the corroborations are such as to almost wholly negative any skepticism, though such extraordinary feats should always be received with caution.