must be pointed out that when the raw or unglycerinated gall was used as the protecting medium, a certain small proportion of cases contracted severe and even fatal attacks of rinderpest; though whether this was due to the gall itself or to the accidental contamination with virulent blood is not stated in the report, though we should imagine that this latter accident might be by no

means uncommon.

Finally, there is the method based on the use of the "anti-bodies" found in the blood of salted cattle, i.e. cattle that have suffered from a severe attack of the disease, but have recovered. By injecting gradually increasing quantities of virulent blood into such animals, the anti-bodies appear in still larger proportions in the blood, and can then be used either in the form of a serum solution or as a defibrinated blood solution. This serum may be used to confer such a degree of passive immunity on the animal, that it either escapes the disease altogether, or contracts it in a much modified form; again, the serum may be used to cure an animal in which there is already a rise of temperature accompanied by other signs of a naturally acquired attack of rinderpest.

All these methods have now been used at the Cape, and it may be of some interest to our readers to learn what is the consensus of opinion as laid down in the Resolution of Conference. It is agreed "that inoculation with bile, either pure (Dr. Koch's) or glycerinated (Dr. Edington's), should not be adopted in any district in which it has not already been commenced, as more satisfactory and more permanent results are obtained from the use of serum, and the latter method can be more successfully applied in clean herds than in herds which have been previously inoculated with bile."

The "Conference" then arrive at the conclusion that it is better not to recommend that the inoculation with Koch's bile should be followed by an inoculation with virulent blood on the tenth day, as formerly recommended, as it is found that unless this blood inoculation is followed by a decided reaction-which occurs very rarely-the immunity already conferred by the bile is not increased. It is recommended, however, that in the case of dairy cattle which have already been inoculated with Koch's bile a second bile inoculation may be made, as this will confer a protection for several months, and at the same time will not interfere with the secretion of milk.

The glycerinated bile method should be followed on the tenth day by the inoculation of one-tenth of a c.c. of virulent blood; and although a second blood inoculation fourteen to seventeen days later increases the active immunity in certain cases, its use has been followed by considerable mortality, and the Conference, while not opposing a second inoculation of blood, does not recommend its universal adoption, as it is attended with considerable risk.

There appears to be a decided opinion that serum, when properly prepared, is superior to, and much more convenient for use than defibrinated blood, and its use is strongly recommended in preference to the latter when it can be obtained, though it is also recommended that a certain number of fortified salted cattle -i.e. immunised cattle-be sent to districts far removed from centres where serum is prepared, in order that defibrinated blood may be prepared in cases of sudden

emergency.

It seems to be the general experience (as in other diseases in which the serum treatment is used) that in healthy herds the use of serum alone does not confer a very permanent immunity; it is therefore considered necessary, in infected districts, to infect healthy animals with rinderpest, and keep the attacks under control by means of the serum. This may be most safely and satisfactorily accomplished by injecting virulent blood subcutaneously on one side of the animal, and serum on the other. If necessary, i.e. if the disease takes

too active a form, a fresh dose of serum will usually enable the animal to pull through the attack. For all practical purposes, however, it has been found that clean herds, in which there is no disease already, should not be inoculated with serum until the disease makes its appearance amongst them, or in their immediate neighbourhood. The whole of the animals should then be injected, after which, or simultaneously, they may be injected with virulent blood, or be kept in close continuous association with infected animals by kraaling them together every night. In this way the animals become salted or protected; under these conditions the immunity produced is active and of long duration, as opposed to the temporary and passive immunity that is conferred by serum when used alone, and perhaps also by bile. Where bile has already been inoculated, it is no use to inject serum and then virulent blood; for, as already mentioned, the immunity conferred by the bile varies very greatly in degree in different cases. Where such bile inoculation has been resorted to, the most satisfactory course for the owner to pursue is to keep a supply of serum by him and inject all cattle as soon as they are observed to be ill, or as soon as the thermometer indicates a rise of temperature. Where serum cannot be obtained, as already mentioned, the blood from salted cattle may be used. These salted cattle are usually fortified by injections of virulent blood, commencing with 10 c.c., and then going to 20, 50 and, lastly, 100 c.c. at intervals of ten days. Either serum or blood is injected in quantities of 100 or 200 c.c. into the animals suffering from the disease. This injection may be made subcutaneously, and not into the muscles, either behind the shoulder or into the dewlap.

It is, perhaps, too early to be dogmatic on the question of the best method of treating cattle for the prevention and cure of rinderpest, but when the exceedingly fatal nature of the disease is borne in mind, and when it is remembered that the disease is so markedly infective and fatal that whole herds are practically exterminated when once the disease is introduced (the objections that are brought forward against inoculation against anthrax, that the percentage mortality from inoculation is almost or quite as great as the percentage mortality from the disease itself not holding good in this case), it is not to be wondered at that the South African farmers received with enthusiasm any method which would preserve to them even a large percentage of their cattle, and that many of them were quite willing to run the risk of introducing rinderpest through the bile inoculation if they could only be sure that some 60 or 70 per cent. of the so infected animals would recover, and would then be protected to a certain degree against future attacks.

As Koch's bile method complied with such conditions it was undoubtedly a marked step forward, whilst it also made it possible to obtain salted cattle with which serum experiments might afterwards be carried out.

These serum experiments-showing that in serum the veterinary surgeon has in his hands a weapon by using which he is able to control the course, even of a severe attack of rinderpest-have given the farmers confidence enough to make them actually anxious to produce the disease under such conditions that they may keep it under control, and so salt their cattle artificially; thus rendering them immune for a considerable period against infection, even of the most virulent character.

With the vast agricultural and cattle-breeding interest at stake, we may anticipate that Koch's earlier experiments will, in the very near future, be improved upon, that South African cattle raisers and dealers will in the long run be enormously benefited, and that a source of wealth, which until a very short time ago was threatened with almost immediate extinction, will continue to be one of the principal resources of a great and flourishing colony.

LARGE REFRACTING AND REFLECTING

TELESCOPES.

THE HE Yerkes Observatory, which has recently been completed and inaugurated, contains in its instrumental equipment the largest refractor in the world, the diameter of the object-glass spanning 40 inches.

The late Mr. Alvan Clark, the constructor of the lens in question, expressed the hope that still larger apertures might be successfully made, but he pointed out that the effect of flexure in larger discs was to be mostly feared, although he felt that it might be perhaps possible to still further increase the aperture without endangering the performance of the objective. Being therefore apparently near the limit to which such large objectglasses can be successfully constructed and mounted, it is only quite natural that attention should be turned to the other form of telescope, namely the reflector, and inquire whether this type of instrument is restricted in the same way as the refractor, or whether it can step beyond these bounds and open up fields which would otherwise be lost to us.

Discussions as to the capabilities of these two types of telescopes have been very rife, and while some observers hold that the reflector is the instrument of the future, others again take the other side and advocate refractors. It is now generally conceded that for definition the refractor is the instrument par excellence, but for purposes where light-grasping power is the main requirement the reflector takes the first place. In the cases of very large apertures reflectors can be made of diameters far exceeding anything that can be attempted for refractors. A point of initial importance in large instruments is the question of the focal length of the object-glass or mirror, as the case may be, for on this factor depends the length of the telescope tube. Now if this be of considerable length, the telescope mounting and dome have to be of considerable proportions, rendering the instrument both expensive and subject to many possible errors. To retain the size of the aperture of the instrument and reduce the focal length is a natural means of overcoming this difficulty, and this has been attempted in many instruments. Such a reduction is, however, accompanied by several optical drawbacks which detract from the efficiency of the instruments.

In the case of reflectors of large aperture and very short focal length a most striking deficiency becomes apparent, and, curiously enough, this has practically been passed unnoticed until Prof. Schaeberle (Astr. Journal, vol. xviii. No. 413) quite recently brought attention to it. So large is this source of bad definition, that he refers to it as a "fundamental optical defect." How he came to alight on this source of blurring factor will be best gathered from the following brief extract in his own words.

"On a very favourable night, I recently had the opportunity of testing the great Crossley reflector of the Lick Observatory, and found the surface of the same to be a practically perfect paraboloid of revolution; but on examining certain celestial objects-Saturn among others -I was very much surprised to find that the instrument failed most signally to come up to expectations. While puzzling and pondering over the probable cause of the poor results given by what I knew to be a finely figured surface, it occurred to me to ascertain the exact amount of the error introduced in the form of the image, resulting from the well-known fact that the focal point is not at the centre of curvature of the parabolic mirror."

To understand the origin of this bad definition, one must imagine a small circular disc situated in the focal plane of the paraboloid of revolution, and concentric with the optical axis. Viewing this disc from different points on the surface of the mirror, it is obvious that it will appear circular only when the eye is in the optical

axis, but in all other positions it will appear elliptical, the eccentricities of the ellipses becoming greater the further the eye is moved away from the optical axis. Further, the angular diameter of both axes of the disc will decrease as the eye moves away from the optical axis, in consequence of the increase in distance from the focal point. The result of such a source of error as this would be that if the rays from the components of a double star be reflected by the mirror, the linear distance between their focal images as formed from different areas along any radius of the mirror will vary from a minimum for the area on the optical axis to a maximum for that area furthest away. In the case of a planetary disc, there will be produced a blurring effect caused by the numerous images of different sizes overlapping one another.

Having investigated this source of error, Prof. Schaeberle made a comparison of the efficiency of the more prominent reflectors now in use. The result is of such interest, that we must refer to it at some length.

In the following table the blurring effect for each mirror is tabulated in the fourth column, the fifth and angular diameters of the outer ring of Saturn and the sixth columns representing the computed difference of solar or lunar disc based on the given ratio of diameters.

The last column gives the values for the limiting radius of the field of view of best definition for each telescope, on the assumption that the radius of the field of measured distances with the optical axis as centre, does not exceed a value which would introduce an error of more than o"05. The most striking feature of this column is the smallness of the fields in the several cases mentioned which are not influenced by this error.

A glance down the fifth column brings out clearly the fact that the smaller the ratio of focal length to diameter of mirror, the larger the difference of angular diameter of the objects observed. Thus in the case of the Draper, Schaeberle, and the two Lassell instruments, where this ratio is comparatively large, about 9: 1, the differences are small, while for the two Common mirrors and Schaeberle's 12-inch, where the mean ratio is approximately 4: 1, the differences increase very rapidly.

Not only will this blurring effect, caused by these differences of angular diameters of the images, be notably increased as the focal length is decreased, but the greater diameter of the image, and therefore distance from the optical axis, will bring this defect more in evidence.

The main result of the investigation, summed up in a few words, is that large parabolic mirrors having a ratio of focal length to aperture less than fourteen to one are, as regards definition, "theoretically unfit for making observations of extreme delicacy." It may be mentioned that this defect does not mar the efficiency of such instruments for certain kinds of work, such as spectroscopic, bolometric, &c.

the Altai wapiti, a species first made known in this country by antlers obtained by the second Yarkand expedition in Kashgar, and described by Mr. Blanford. The herd includes the first living examples of this splendid species ever brought to this country, although visitors to the Zoological Gardens have now an opportunity of seeing an immature specimen. And it is not a little remarkable that a stag so well known in the Altai, where it is kept in a semi-domestic condition by the farmers, should so long have remained a stranger to the menageries of Europe.

Perhaps, however, the most generally attractive of all the enclosures is the one which may be called the Chital paddock, on account of its containing a large herd of the beautiful chital or Indian spotted deer. A most successful photograph of a group of deer feeding in this paddock, for which we are also indebted to Her Grace the

case, and whereas these animals thrive and multiply at Woburn to an extraordinary degree, some northern species, like the elk and reindeer, which might have been expected to flourish best, die off in an unaccountable manner. Out of several head of American elk only a solitary survivor now remains, while all the adult reindeer are dead. Some young American calves of the latter species have, however, been recently received, and it may be hoped their fate will be happier. Possibly if Norwegian reindeer and elk were tried, they might do better than their American representatives. But it must be remembered that both these animals have disappeared at a comparatively recent date from Britain; and there may be something in our climate at the present time absolutely unfavourable to their existence.

The various Oriental races of sambar and rusa flourish at Woburn equally well with the chital, and the large

Duchess of Bedford, forms the subject of the second illustration. In addition to numerous chital, easily recognised by their dappled coats, this photograph shows several examples of the true maral, or Caspian red deer, from the Caucasus, which are the largest animals in the photo. This deer, it may be observed, although often regarded as a distinct species, appears to be nothing more than a race, or sub-species, of the red deer of Western Europe. Of the other smaller animals in the group, a Virginian deer occupies the foreground on the left, while several mouflon, and at least one Indian antelope, or black-buck, are in the

centre.

From the torrid nature of their environment, it might have been supposed that the Indian chital and blackbuck would have been among the species least suitable to withstand our climate. Nevertheless, this is not the

series of these animals now collected there affords material for a fairly full study of an exceedingly difficult group. Hog-deer and muntjacs are also among those which are hardy and capable of acclimatisation. Other Oriental species represented in the collection are the swamp-deer of India, and the thameng of Burma and Siam; but these are kept in smaller and well-protected enclosures, with ample shelter. From the colder nature of their habitat, the various species and races of the sikas of Japan and Northern China might naturally be expected to do well, and as a matter of fact this has been found to be the case. In addition to the common Japanese and Manchurian sikas, the collection includes the large and handsome Pekin sika, previously known only by the type specimens sent home by the late Consul Swinhoe after the sack of the Imperial Summer Palace. Père David's deer has been already mentioned as among

those running at large in the park, and there is good prospect of the herd of this aberrant and interesting species increasing in number. A solitary male of the previously imperfectly known Bedford's deer (Cervus xanthopygus) has unfortunately succumbed to a lingering decline, although happily not till it exhibited the remarkable variation between the summer and winter pélage. Roe deer, of course, flourish; and recently there was the opportunity of seeing the European, Siberian, and Manchurian species, or races, living side by side. The rare Chinese water-deer (Hydropotes) is represented by a single doe, which exhibits to perfection the skulking habits peculiar to the species; but a specimen of Michie's tufted deer, which formerly was one of the attractions of the collection, now adorns the museum at the Abbey. Musk-deer do not belie their hardy nature, and it is one of the most interesting sights in the park to

marsh deer and pampas deer. Young examples of each of these two latter are, however, at the present time in the collection, and as they are very carefully tended, and the experience derived from their predecessors is available, it may be hoped they will survive. A tiny little deer, apparently referable to Mazama gymnotis, is also among the newest arrivals, and its career will naturally be watched with deep anxiety. Brockets have been tried with hopeless ill-success, and the attempt to acclimatise them has reluctantly been abandoned.

During the very short period the collection has been in existence it has included, counting red and fallow deer, close on forty distinct species and races-no mean record when it is remembered that the total number of valid forms which have been exhibited in the London Zoological Gardens since its foundation does not exceed forty-eight. As every effort is being made to increase

watch these little deer bounding across their enclosure in the manner so well-known to all Himalayan sports

men.

In marked contrast to the adaptability of the Oriental deer to their new surroundings is the ill-luck attending the introduction of most of the American deer, exclusive of the wapiti. The only exception to this is the Virginian deer, which flourishes and breeds, some mingling with the chital herd, others roaming at will in the open park, and a few taking up their abode in the immediate vicinity of the Abbey itself. These latter exhibit tameness and fearlessness to an extraordinary degree-only, indeed, exceeded by the members of a little herd of roe from the Caucasus, one of which permits itself to be fondled like a pet lamb. Black-tailed and, we believe, mule-deer have been tried without success; while the same ill-fate has attended several examples of the South American

the Woburn collection, it bids fair to beat the record in the number of species, as it already does in individuals. R. L.

THE LATE PROFESSOR A. SCHRAUF. THE HE comparatively small number of mineralogical workers and teachers has been once more diminished, and to the recent deaths of Mallard, Daubrée, DesCloizeaux, Sohncke, Retgers, Kenngott, Haughton and Heddle, must now be added that of Albrecht Schrauf, Professor of Physical Mineralogy in the University of Vienna, who has passed away, after long illness, near the end of the sixtieth year of his age. A. Schrauf was born on December 14, 1837; he became assistant in the Mineral Department of the Imperial Museum of Vienna in 1861, and Keeper in 1867; after