optical puzzle than was the case with the lower powers; in fact, the effect obtained was one which, if it had occurred in any object where there were fibres or striæ crossing each other in a similar way, would easily lead to the true character of such an object being mistaken.

There was one other little matter which he thought it might be of some interest to mention. Among the species of black fungi which were found infesting orange and other trees, and which appeared in great abundance last autumn, one attacked a bay tree or true laurel growing out of doors, and it seemed able to remain and grow upon the leaf for a long time without injuring it. Many of the leaves which he had examined did not seem at all damaged, although the fungi had remained upon them from last autumn to the present time. It was quite easy to take them off with a penknife, and as there was no penetration of the fungus into the structure of the leaf, as soon as the film was removed the leaf seemed all right again. A fungologist to whom he had shown it, thought it to be a species of Capnodium. (Drawings of its general appearance were then made upon the blackboard.) An interesting physiological question arose in connection with it: What was the good of the plant to the fungus if it did not penetrate the structure of the leaf? The respiration of plants was the same in principle as that of animals, but they were also able to do what animals could not do, and that was to digest carbonic acid. Whether any of the matters exhaled by the leaf were of use to the fungus, he could not say. Specimens of the leaves with fungi upon them were then handed round, in the hope that some gentleman present might be able to identify them.

Mr. Thomas Palmer said he had found a very similar fungus recently upon the leaves of the Arbutus. It did not penetrate the leaf, but was merely a kind of surface fungus, and could be readily brushed off by tolerably stiff bristles. He had, however, observed that when the black mass had been removed, the leaf underneath was of a much lighter colour than the surrounding parts.

The President had found a number of small beads, in irregular grape-like groups, in connection with it, which he thought might possibly be spores.

Mr. Vize said that, without examining the specimens more closely, he could not determine the species; his impression, however, was, that it was an immature form of Capnodium, which, as a rule, it was very difficult to find in England in the mature state. Under a bell glass, with sufficient warmth and moisture, they could be got to develop more fully.

The President inquired if Mr. Vize could answer the question, of what special use was the plant to the fungus; what caused it to establish itself there?

Mr. Vize could only suppose that the spores had dropped at some time upon the leaf, and having found a nidus, had there developed. It was well known that the spores were carried about in the air, and that special spores were developed in special positions which happened to favour their habit of growth.

Dr. M. C. Cooke, in reply to a question from the President, said

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that the drawings made upon the black-board sufficiently convinced him, without looking further at the specimens, that the plant which they had there was one which was common on almost all the hard-leaved shrubs, Capnodium Footii. It was the early condition of it, and beyond which it seldom proceeded farther in this country. It consisted chiefly of a pellicle of mycelium, the free cells of which gave rise to the quantity of threads shown. In the fourth volume of the Journal of the Horticultural Society they would find a paper upon the subject by the Rev. J. M. Berkeley and Desmazières, in which it was fully described, and which, he believed, gave rise to the genus Capnodium, which at present contained three species, of which this one, C. Footii, was the most common. With reference to the pellicle being so easily removed, he had the honour of reading a paper before the Royal Horticultural Society upon this subject, and the conclusion at which he then arrived was that in many cases it appeared that this fungus developed itself upon the honey dew and other secretions upon the surface of the leaf. For instance, the lime tree was well known for the quantity of sweet matter found upon its leaves, and in the autumn it was not unusual to find almost every leaf affected by a black, sooty appearance, which was nothing more nor less than Capnodium, and it appeared certain that this fungus drew its nutriment from this secretion of saccharine matter either by some of the Aphis tribe or by the plant itself, without striking at all into the substance of the leaf.

The President felt sure they were all very much obliged to Dr. Cooke for the very interesting remarks which he had made. It showed that if the Fellows of the Society would sometimes mention things which came under their notice, it might, as in the present instance, lead to a very interesting communication from some one present who might be qualified to give them the further information which they required.

The following gentlemen were elected Fellows of the Society: Mr. Amos Hobson; Mr. George Brook; Mr. G. A. Woods; and Mr. Frank Campion.

SCIENTIFIC EVENING, May 15, 1878.

The last scientific evening of the session was held, by kind permission of the authorities, in the libraries of King's College, on the 15th of May. There was a good attendance of the Fellows, and as the subjoined list will show, apparatus and objects of great interest were exhibited. The Society were indebted to Messrs. How and Co. and Mr. Baker for the use of a number of excellent lamps.

List of Objects Exhibited.

Mr. J. Badcock: Fredericella sultana, and a supposed new ciliated Infusorian.

Mr. J. W. Bailey: Folding microscope with large stage, and nummulitic limestone.

Mr. Charles Baker: Zeiss' new oil immersion object-glass not requiring correction.

Mr. Thomas Bolton: Hydatina senta.

Mr. J. Browning: Stained and injected preparations illustrating the anatomy of the Frog; and a new lantern microscope with oxyhydrogen light, for use with ordinary objects and slides.

Mr. J. C. Burch: New reflecting micrometer.

Mr. Rochford Connor: A set of beautiful drawings of microscopic objects, comprising Foraminifera, Polycystina, Diatomaceæ, and other objects.

Mr. Frank Crisp: A pair of large Nicol's prisms 12 inches long, with 3 inches clear field; a set of large quartz crystals 3 inches over, and other objects for exhibition with the prisms. Made by Mr. Ahrens.

Mr. Thomas Curties: Lophopus crystallinus; a selection of the Rev. J. Vize's micro-fungi mounted, and a collection of Professor Cleve's diatom slides.

Mr. F. Enock: Some insect preparations mounted without pressure; tongue of Cerceris arenaria, &c.

Mr. F. Fitch: Reproductive organs of Nomada lineola, both male and female; a parasitic bee, &c.

Mr. C. J. Fox: Mica combination of twenty-four films, showing by polarized light the first three orders of the Newtonian spectrum, divided into eighths; mica combination of eighty-four films, showing Airy's spirals; and crystals of sulphate of cadmium, with polarizing apparatus rotating by clockwork.

Mr. W. H. Gilburt: Section of yew, Taxus baccata.

Dr. W. J. Gray: Fungoid cancer of mamma, double stained by Mr. Cole.

Messrs. How and Co.: Sections of rocks, lherzolite from the Pyrenees, Cornish serpentine, and hornblende schist.

Dr. Millar: Sections of Acarnus innominatus, and one showing that the recurved spicules figured by Carter as Acarnus innominatus is a distinct sponge.

Mr. A. D. Michael: A new species of Cheyletus, proposed to be called C. flabellifer.

Mr. Fred. Oxley: A supposed new species of Ecistes.

Mr. B. W. Priest: A sponge, Halyphysema tumanowiezii.

Mr. G. P. Price: Some anatomical preparations, injected intestine of rat, duodenum of rat, &c.

Mr. A. Pumphrey exhibited and described his new process of autographic printing, which he illustrated by means of a sketch brought by a Fellow to the meeting.

Messrs. Ross and Co.: New Zentmayer microscope-stand with recent improvements, and Wenham's high-power binocular prism, showing the Podura scale with and object-glass.

Mr. W. W. Reeves: Callidina sent up by Lord S. G. Osborne during April, 1873, and kept alive by having water put to them about once in six or seven months.

Mr. H. J. Slack: Cheyletus eruditus and other mites.

Mr. James Smith: Specimens of leaves, showing hairs and spines. Mr. H. C. Sorby: Drawings made with pigments from human hair, one red and the other black.

Mr. Charles Stewart: Sporogonia of Funaria hygrometrica, and some new Polyzoa.

Mr. Amos Topping: Various patterns of grouped Polycystina, and some injected preparations mounted in balsam, but preserving the true form as in fluid mounting.

Mr. F. H. Ward: New form of micro-spectroscope; spectrum of didymium, didymium glass, &c.; and sections of the stem of Eucalyptus stained with carmine, logwood, &c.

Mr. Robert G. West: Lissajou's curves on glass slides for the microscope.

KING'S COLLEGE, LONDON, June 5, 1878.

H. J. Slack, Esq., President, in the chair.

The minutes of the preceding meeting were read, and were signed by the President.

A list of the donations received since the last meeting was read by the Secretary, and the thanks of the Society were voted to the respective donors.

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The President said that under the old practice of the Society its meetings took place on the second Wednesday in the month; but when the Monthly Microscopical Journal' was commenced, it was represented to them by the Publisher that this did not give sufficient time to allow of the Proceedings' appearing in the next monthly issue. On this account their night of meeting was altered to the first Wednesday in the month, which had been found to clash with the meetings of the Geological Society and some others, to the great inconvenience of many of the Fellows. Under the new arrangements for the Journal there would be no difficulty in regard to the publication of the Proceedings' if their meetings were held later in the month; and it had therefore been suggested that they should revert to the original plan of meeting on the second instead of on the first Wednesday in the month. Their next meeting would not take place until October, before which time a new list of meetings would be issued, and in which the alteration would appear. It was not quite formal to bring the question before an ordinary meeting, but the Council-with whom it rested to make the change-thought it better to mention it this evening, so that if any Fellow had any objection he might be able to state it. All that the Council wished was to accommodate the greatest number as much as possible.

There being no objection raised, the President formally announced that in future the meetings of the Society would be held on the second Wednesday in each month during the session.

The President said the meeting would be pleased to hear that they were favoured with the presence that evening of Professor Stokes, Sec. R.S., who had come up from Cambridge to read a paper he had prepared on the angular aperture of object-glasses, and which it was considered would entirely dispose of the points formerly in controversy on this question. Before he read it, the Secretary would read a note by Professor Keith, bearing on the same subject.

Mr. Frank Crisp (Secretary) then read the note by Professor Keith,

which was entitled "On the Results of a Computation relating to Tolles' Objective." It was accompanied by photographs of the Professor's computation and of his diagram of the objective, showing the lenses of which it was composed and the path of a ray through it.

Professor Stokes, after disclaiming for his paper all the importance attached to it by the President, proceeded to read it with comments, illustrating it by reference to diagrams, and by drawings upon the black-board.

Mr. Ingpen ventured to make a few remarks on the practical bearing of the paper they had just heard. The theory was evidently correct, and would not be doubted by anyone acquainted with the more advanced optics, but there was some practical difficulty in securing an illuminating pencil which could utilize the increased angle of aperture obtained by the new arrangement. This could not be done by any ordinary condenser, where the light impinged upon the under side of a flat surface, but it was effected by Professor Abbe's immersion illuminator, and others constructed on similar principles. Another difficulty-one for the optician-was to construct such middle and back combinations for the objective as would utilize the large cone of rays entering the front hemisphere. This Professor Abbe had certainly achieved to the extent of 113°, which was a great advance on all previous apertures.

Mr. J. W. Stephenson (Treasurer) said it was true that they were limited to an equivalent angle of 180° in air if they had a plane dry surface beneath the slide; to get the full effect they must, of course, have some medium to connect the condenser with the balsamed object instead of air; Professor Abbe had now devised an immersion condenser having a balsam angle of 138°.

Mr. Mayall, jun., said that Professor Abbe had not been the first to devise means of illumination far exceeding the limit that obtains when the base of the slide is flat and dry. A lens almost exactly similar to Professor Abbe's was figured by Mr. Wenham in the Quarterly Journal' more than twenty years ago, and the purpose was the same,— to obtain extremely oblique illumination. Mr. Wenham suggested its use with the paraboloid. Then we had the reflex illuminator, that works well up to a moderate limit; the immersion semi-cylinder that permits the rays to fall on the object, when mounted on the slide or in balsam, at an inclination approximating to 90° in glass, and various forms of immersion prisms, among which Dr. Woodward's is particularly practical. He did not understand Mr. Ingpen's difficulty in providing oblique rays of sufficient intensity for practical use, as the difficulty he had found was to regulate the amount of the light, not its obliquity. For example: by blocking out the whole of that part of the illuminating pencil on a balsamed object that corresponds to the air pencil of 180°, and using only rays beyond this inclination, he had found, with objectives having balsam angle of 95° and upwards, the more difficult images were made more appreciable by the eye. It appeared to him it was the excess of angle beyond 82° in glass of the illuminating pencil that enables us to see the more difficult images; and so it is with the aperture of the objective. In the demonstration