the requisite corrections, so that we may be able to foretell how much the range will be increased or diminished by the wind, and what allowance should be made in the direction of the projectile to the right or left. The results of Major Maitland's observations are of value to others besides military authorities, inasmuch as they give a means of determining the velocity of the wind at considerable elevations above the ground. The theoretical investigations given by him depend perhaps too much upon the assumption that the pressure of the wind against the projectile is inversely as the square of the velocity of the wind, according to the formula of Sweaton. But the actual observations quoted by him form an acceptable contribution to our knowledge on this subject. A wind whose velocity is estimated at twenty miles an hour produces, according to his observations, a deviation of thirtyeight feet in a range of two miles, the diameter of the projectile being six and a quarter inches.

THE BRAYTON READY MOTOR.

Mr. Brayton has lately brought before the public a gas-engine, in which sixty pounds' pressure may be generated within the space of one minute, and which can be started by the application of a match with almost the facility that gas may be lighted. In construction this new motor, which has lately figured in the proceedings and discussions of several of our Mechanics' Institutes, closely resembles the steam-engine; its cylinder and piston, valve-gear, and connections being essentially the same. The principal difference consists in the addition of a compressing-pump and a reservoir, for the purpose of compressing and of retaining a quantity of combustible gases, mixed with a proper proportion of air for its complete combustion, and at a pressure exceeding that which it is proposed to have exerted in the working cylinder. A "jacket" surrounds the cylinder, through which water is kept constantly circulating. The comparatively low temperature thus secured in the walls of the cylinder allows of the employment of the piston with packing rings which has become the standard for the steam engine, and likewise of the same method of lubrication. A diaphragm similar to that which gives the Davy safety-lamp its security, and composed of several layers of wire-gauze, is placed at the opening

through which the gaseous mixture enters the cylinder. This is of more closely woven material than that used in the safety-lamp, and several thicknesses are employed, in order that it may act as an effectual preventive against the communication of ignition to the mass of gas inclosed in the reservoir. A similar diaphragm, but of much smaller area, allows a very small quantity of gas to stream continuously into the cylinder, and as this current is not interrupted by the closing of the induction-valve, its little jet burns constantly, and is always ready to ignite an entering charge. A safety-valve of large area is provided as a precaution against the possible accident of the flames reaching the reservoir.

The burning-gas employed and the air are taken in proper proportions into the compressing-pump, and from this are carried forward, intimately mixed, to the point at which the mixture is to do its work; by this means complete combus tion is insured. In the machines of this type in operation at the time of this writing crude petroleum is employed in place of gaseous fuel, and the reservoir is filled simply with air which is carburetted at the point of combustion. It thus becomes possible to operate with but a very minute quantity of liquid in the apparatus at any one time, and an explo sion is practically impossible from the fact that the explosive mixture is not formed until it arrives at the combustion chamber.

The induction-valve is protected from the action of the hot gases by the safety diaphragm which is interposed between it and the cylinder. Upon the opening of the inductionvalve the mixed gases enter, and are promptly ignited by the constantly burning jet before described. The inventor of this ingenious mechanism claims that the operation of his engine is precisely similar in the action of the engine proper and in the distribution of pressure in its cylinder to that of the steam-engine; that the entering mixed gases burn stead ily-not explosively-as they flow into the cylinder; and that the pressure from the commencement of the stroke to the point of cut-off, as proved by indicator diagrams, is as uniform as that observed in any steam-cylinder.

M. TECHNOLOGY.

RECENT PROGRESS IN PHOTOGRAPHY.

The success attending recent experiments in photography seems to justify the expectation of an early revolution in the manipulations of some of its fundamental processes. In the negative process, all the more vexatious and uncertain details have been in a great measure eliminated, and the practice of this branch of photography has been adapted to even the ordinary tourist. The collodion negative process, which displaced the daguerreotype process, about twenty-five years ago, as much by reason of its wider range of applications as because of its comparative simplicity and certainty, has remained essentially the same as when first introduced. Improvements in it have been mainly in the detail, and their adjustment to the various applications of which it was soon found susceptible. Its inconveniences, and the apparently needless complexity of its manipulations, were soon felt, and attempts made to remedy them; but the sensitive collodion film is still produced upon the glass plate by the professional photographer by charging it indirectly with the iodide and bromide of silver, sensitive to light. Some soluble iodides and bromides, insensitive to light, are first introduced into the collodion; and after a film of it has been formed upon the glass, it is rendered sensitive by immersing it in a solution of silver nitrate, where the insoluble haloid salts of silver form in the film, while the nitrates of the other bases, previously combined with the halogens, remain in the solution. But besides the complexity of the manipulations, the silver solution is expensive and voluminous, and requires expensive and fragile receptacles; and, withal, has generally been regarded as the most decided variable in the process, and, directly or indirectly, chargeable with most of its failures. In out-door photography, all the inconveniences and uncertainties attending the use of this solution are multiplied to such an extent that, failing in attempts to eliminate it altogether, the best effort, especially of amateurs, was directed to the improvement of the so-called dry processes, in which

plates, prepared up to the sensitive stage, are rendered capable of being kept in that condition by washing them thoroughly with water, then applying some preservative solution, as of tannin, gum, etc., and drying them. Although some of these processes in careful hands have been made to afford very satisfactory results, they are upon the whole inferior to the wet process in rapidity, certainty, and general excellence, in spite of the excessive care and labor required in the preparation and development of the plates. Another plan of relief from the silver solution, which naturally suggested it self at an early day, was the formation of the sensitive silver salts in the collodion, before pouring it upon the glass plate, by introducing into it the silver nitrate and the necessary iodides and bromides. But, after trial, this direct method was regarded for a long time as impracticable, mainly because the iodide and bromide of silver could not be made to form in a sufficiently finely divided condition to remain suspended in the collodion. At last, however, the so-called washed collodion emulsion process has been brought to such a degree of perfection that all the manipulations hitherto found necessary with the baths, washing-trays, preservative solutions, etc., seem to be reduced to the minimum of the one single, simple operation of pouring a sensitive emulsion of the haloid salts of silver with collodion upon the glass plate, and allowing the film to dry. All the articles required are already to be had in the market. The plates thus prepared are said to be of the best quality, of great certainty, and of absolute uniformity, equal in sensitiveness to those prepared by any dry process, and affording a fine film, free from granulation, even under the microscope, and, by regu lation of the development, adapted to the production of neg atives or positives, as may be desired. Besides the freedom from custom-house annoyances that this process guarantees to the tourist, it renders him at all times, as far as the size of his plates is concerned, entirely independent of the size of the receptacles for the various solutions. The first successful experiments in this direction were made by Bolton and Sayce, two amateurs of Liverpool, about ten years ago. They found that by omitting the iodide, an emulsion of bromide of silver with collodion could be formed, suitable for photographic processes. The conditions most favorable to

emulsification have since been most persistently investigated. The first difficulty in the process lay in the inability to introduce the silver nitrate and the bromide employed into the collodion in quantities exactly chemically equivalent; and if the silver nitrate happens to be in excess, fogging the negative results, unless some restraining mineral acid is introduced; while excess of the bromide reduces the sensitiveness of the film to a degree corresponding to that excess, and also exerts a solvent action on the invisible image, unless it is quickly developed. In practice it was found best, therefore, to employ a decided excess of bromide, and then to impart sensitiveness to the film, and prevent any solvent action on the image by washing out the soluble bromide with water. The soluble nitrate of the base, previously combined in the bromide, formed in the film in the operation, although of little consequence in the silver bath in the old process, would also tend to split the film on drying by its crystallization, if allowed to remain in it. All these difficulties were, finally, simply and effectually met by Mr. Bolton by washing out all the crystallizable salts from the emulsion, previously to the formation of a film with it on glass, while a preservative agent was added at the same time. An emulsion was prepared, with only such a degree of care as to the adjustment of the salts that it might give tolerable results, and was then poured into a large flat dish, and the film, when set, was washed several times with small quantities of distilled water, after having been divided into small squares with a silver fruit-knife, until all soluble matter was removed. The very light pellicle, formed by drying the film obtained in this way, contains all the essential ingredients for a sensitive emulsion, seems to keep indefinitely, and only requires simple solution in a mixture of equal parts of alcohol and ether, with the addition of a little alcoholic solution of tannin and of a saturated alcoholic solution of soap, to furnish an emulsion for the preparation of plates for present or future use. Such washed emulsion pellicle, in the form of shreds or powder, can be obtained by mail. The development of a plate is effected by wetting the surface with methylated alcohol and rinsing with water, then treating it with a weak solution of pyrogallic acid for about a minute, and then, whether a feeble picture be visible or not, pouring