brought before the society the most important improvement in the microscope since the days of Mr. Wenham.—Mr. Browning briefly explained his reasons for believing that the second prism used did not produce imperfect definition. The President said that he would confirm Mr. Lee's observations concerning the use of high powers in Mr. Stephenson's microscope. The th had been used with great advantage, and though both the fields of view were not equally illuminated under this high power, it would at once be seen from the construction of the instrument that only the art of the optician was required to make both tubes equally valuable in using high powers. Those who had had the pleasure of examining the instrument as well as himself would bear him out in the statement that the effect of giving an erect image is of the highest importance in cases where dissection was being conducted. The instrument devised by Mr. Stephenson contained no error of importance, and the slight want of flatness in the field could be readily obviated.

Hippuric Acid as a Microscopic Object.—In the Journal of the Quekett Club for April, Mr. T. Charters White gives an excellent account of the crystallization of this substance in order to prepare it for the microscope.

The Comparative Steadiness of the Ross and Jackson Plan of Microscope.— An important practical paper was lately read before the Royal Microscopical Society by Dr. Carpenter, giving the results of his observations on the relative steadiness of these two forms of microscope stands. Speaking of his experience of the two models in the last deep-sea expedition, he said: “When the ship was going under 'easy steam,' with either a fair wind or a light contrary breeze, there was enough general vibration to produce a considerable differential vibration in any microscope liable to it, and thus to occasion a decided tremor in the image even when only moderate powers were employed. But when we were steaming with full power against a head-sea, the general vibration became so great as to be the severest test of the mechanical arrangements of our microscopes. Now, it happened that whilst my own instrument-a portable binocular microscope weighing less than seven pounds, which is my usual travelling companion-is constructed on the Jackson model, Professor Wyville Thomson was provided with an instrument of about the same scale, but heavier by some pounds, made upon the Ross model; and we thus had an opportunity of fairly testing the two plans of construction under circumstances peculiarly critical. The difference in their performance was even more remarkable than I had anticipated. I found that I could use a 1th-inch objective on my own microscope, with an even greater freedom from tremor in the image' than I could use a 3rdsinch objective on Professor Wyville Thomson's. In fact the image'danced' very perceptibly in the latter, even when the 11-inch objective was in use." -Monthly Microscopical Journal, April.

An American Graduating Diaphragm.—Mr. Zentmayer has described an instrument of this kind in the Journal of the Franklin Institute (February. See also Monthly Microscopical Journal, June). It has been described also in the Chemical News by Mr. Henry Morton. It consists of two cylinders or rollers with parallel axes and surfaces in contact, having similar conical grooves on their surfaces, and fine teeth cut at one end of each, which, gearing together, cause them to rotate in unison. There is, theoretically, an objection to a dia

phragm of this construction, from the fact that its opening will not always be in the same plane-that is, the smallest cross-section of the space between the rollers will not always be equidistant from a plane at right angles to the line of sight and passing through the axes of the rollers. With the larger opening, this smallest section will be nearest to, and with the smaller, farther from, such a plane. In practice, however, this difference is so small as to be entirely unimportant, and may even, in some cases, be turned to advantage. There are other forms of gradually adjustable stops which have been employed with more or less success, but few, according to Mr. Morton, involving so many elements of durability and convenience.

Browning's Pocket Microscope.-Mr. John Browning has recently turned out a pocket microscope, which we have much pleasure in commending to the notice of those of our readers contemplating a sea-side tour.

Its

general features are shown in the figure. It has two objectives, 1-inch and 2-inch, and a large-field eye-piece. The workmanship, like that of all Mr. Browning's instruments, whether astronomical or general optical, is excellent. This instrument-the most portable yet contrived-is made with the body in two parts, one sliding into the other; the outer portion also slides down through the opening in the stage, which carries the objects. Two legs are hinged at about the centre of the instrument; the rod or tube, on which the reflecting mirror is fixed, forms a third leg. Thus, when the two hinged legs are open, the instrument has a firm tripod stand. These legs being opened, the lower part of the body drawn up through the stage, and the eye-drawer withdrawn from the body to about the same length is all that is required to set up the instrument ready for use. The tube spoken of as carrying the reflecting mirror and forming one of the legs has a fine screw on the inside, and a milled head at the top. This screw gives a fine adjustment. The instrument has an eye

piece with a large field, and good objectives. The height, when set up for use, is about one foot, and the dimensions of the case which contains the instrument with two objectives, dipping tubes, and pliers complete, is only 63 inches long, 3 inches wide, and 12 inch long.

PHOTOGRAPHY.

Combination Printing.-The advantages of being able to effect a judicious combination print from several negatives are more and more impressing themselves upon the photographer. One of the most familiar examples of this kind of printing is the putting in of skies in prints otherwise quite cloudless. In the early days of the art, a white sky in a landscape was a sine quá non; at the present time such a picture would not be tolerated. The landscape photographer keeps a set of negatives of clouds taken under different conditions of lighting, so that he can select for any landscape a fitting sky. This is the easiest kind of combination printing, because it does not require any exactness in registration; but far different is the case when a number of figures have to be printed with a landscape background from different negatives: here the greatest mechanical nicety is required to prevent the junction-line of the two from being noticed. To such a state of perfection has this department of photography now been carried, that it is not merely possible but quite easy to combine the parts of several negatives in one print, in such a manner as to produce a mechanically perfect whole— whether it be artistically perfect depends of course upon the harmony that exists between the several pieces of which the picture is made up. A landscape lighted from the right while its figures are lighted from the left furnishes an example of incongruity. Within the past few weeks, a patent has been obtained by Mr. B. J. Edwards for a printing frame, so constructed as to permit of combination printing being effected with the greatest possible efficiency; and as a result of what may be obtained by its means, it will be easy to have a photograph of one's own drawing-room taken (which requires a very long exposure in the camera) and introduce in it the members of the family, taken in the photographic studio under those circumstances of lighting most conducive to success in portraiture. This kind of printing is invaluable for picnic groups, cricketers, and other bodies, who may be singly taken in the studio, and yet form a completed group arranged in their field—a negative of which will have been separately taken.

Photographic Journalism.—The demise of a weekly journal, The Illustrated Photographer, is announced. The reputation it bore was latterly of an unfavourable kind, a good deal of personal and scurrilous matter having been introduced, without a corresponding counterpoise of ability. Its best illustrations, too, had occasionally done previous duty in the pages of other illustrated periodicals; and this, together with incompetency in the editorial management, could lead to no other result than that which has befallen it. There are now only two journals devoted to photography in this country— viz. The British Journal of Photography, which is in its seventeenth annual volume, and The Photographic News, in its fourteenth volume. The Journal

of the Photographic Society now contains only the transactions of that body, and is only published when a meeting of the Society is held, or eight times a year. Several of the foreign journals live, for the most part, on the English ones; the once original Humphrey's Journal (New York) is probably the most noted specimen of this class.

Permanence of Photographs in Asphaltum.-The durability of photographs obtained by the Pouncy process has been called in question. The process is based on the fact that bitumen of Judea, when dissolved in a suitable menstruum and applied to paper or any other surface, is rendered insoluble in proportion to its exposure to light. This property of asphaltum has been long known, but Mr. Pouncy mixes with it printers' ink; hence when the photograph is developed by turpentine the blacks are composed of printers' ink and bitumen. The question that arose is this-Seeing that bitumen is regarded by artists with very great aversion on account of its notorious bad qualities as a permanent pigment, will not its presence in the blacks of Pouncy's photographs be also objectionable? To this Mr. Pouncy replies, in effect, that the blacks or body of his pictures are not formed of bitumen alone, but of printers' ink mixed with it; that only the merest trace of bitumen is present in them, and that this portion is so altered by light as to have become incapable of "running" or cracking-the objections urged against bitumen when used as a pigment by the painters.

Negatives on Paper.-An effort is being made to reintroduce the taking of negatives on paper instead of on glass. A peripatetic photographer who desires to obtain-say-fifty views while on his travels will find an astounding difference in weight between fifty stout plates of glass, twelve or eighteen inches in dimensions, and the same number of leaves of paper the same size. Why paper should not be more used for negative purposes than it is we cannot say. The negative is taken upon, not in, the glass plate, and one would think that the same sensitive coating that is applied to the glass might also be applied to the paper. If this can be done successfully, which, from experiments now in course of being made and recorded, appears to be the case, then will a very great advance indeed have been made in photography as applied to the resources of the traveller.

New Salting Agent for Paper.-Some French photographers are recommending chloride of aluminium for salting paper instead of the chlorides of sodium and ammonium generally used at present. The chief advantage of using this salt appears to be that the image is retained well on the surface, and that consequently the details in the shadows of the print are better rendered.

Niepce de St. Victor.-Photographic science has received a sad loss by the death of M. Niepce de St. Victor, which occurred on April 7, after a few minutes' illness. He was seventy-two years of age. To him we owe very much indeed, including photography on glass plates, and printing upon albumenised paper. From 1847 to 1862 he presented to the Academy of Sciences in Paris no fewer than twenty-six mémoires, the subjects of which were chiefly photography on glass, photographic engraving, and heliochromy. His family being left unprovided for, photographers throughout Europe are making a subscription for them.

PHYSICS.

A Spectroscope for the Invisible Rays at the Red End of the Spectrum.— The Council of the Royal Society recently voted some funds to Mr. C. Brooke, F.R.S., for the construction of a spectroscope to search for lines in the invisible rays beyond the red end of the spectrum. The instrument is now in course of construction by Mr. Browning, F.R.A.S., and the prisms, which are made of rock-salt, have already been ground, polished, and tested. As glass stops many of the ultra-red rays, it is necessary to use lenses and prisms of rock-salt. When the apparatus is finished, a spectrum will be projected on a screen, and then search will be made for the lines by means of a delicate thermo-electrometer, with a thermo-pile having a fine slit in front. "It is found that the lines in the visible part of the spectrum contain no heat, so it is supposed that no rays of any kind fall at those points."

Physical Science at Cambridge.-After a series of long discussions and a considerable degree of opposition the new chair of Physical Science is about to be established at Cambridge. The Syndicate appointed for the purpose had to give up the notion of raising the funds by subscription from the several colleges. They confined their attention, therefore, to the means of raising sufficient funds only for carrying out the recommendations of the Physical Science Syndicate in their report dated Feb. 27, 1869. These were to provide the stipends of a Professor of Experimental Physics, of a demonstrator, and an attendant, requiring altogether a sum of 660%. per annum; also to provide a capital sum of 5,000l. for a new building, and 1,3001. for apparatus. The Syndicate are of opinion that these sums may be raised from the ordinary sources of revenue of the University, and that a small addition (viz. 2s. a head) to the amount of the annual capitation tax will suffice for the purpose.

Fall of a Large Meteorite.-At the meeting of the Geological Society on March 23, Mr. R. H. Scott, F.G.S., communicated an extract from a letter addressed to him by M. Coumbary, Director of the Imperial Observatory of Constantinople, containing an account received from M. L. Carabello of the reported fall of a large meteorite near Mourzouk, in the district of Fezzan, in lat. 26° N. and long. 12° E. of Paris. It fell on the evening of the 25th December last, in the form of a great globe of fire, measuring nearly a mètre in diameter; on touching the earth it threw off strong sparks with a noise like the report of a pistol, and exhaled a peculiar odour. It fell near a group of Arabs, who were so much frightened by it that they "immediately discharged their guns at this incomprehensible monster."

Meteorological Observations in the Captive Balloon.-The yearly Report of the Aeronautical Society contains an account by Mr. Glaisher, F.R.S., of the results obtained by him in his observations of the thermometer and barometer in the Captive Balloon. He says that the Captive Balloon supplied, in a most admirable manner, the power of repetition of observations within 1,000 ft., which no free balloon could do. Our knowledge of the humidity of the air, and of its temperature up to this elevation is very limited. Every ascent in the free balloon had proved that the theory of the decline of 1° of temperature in every increase of elevation was erroneous. In some ascents a decrease of more than 1° was met with in the first 100 ft., notwithstand