IT has been pointed out that the mechanical aids which man has devised to assist him in his varied pursuits of daily life are subject to an evolution precisely similar in character to that which governs the development of living organisms-. ,. In this evolution of our mechanical adjuncts there is a tendency to transfer to them a greater and greater share of the functions originally performed by man himself. Thus the rude implements of primitive man, the cudgel, the stone hammer, may be regarded as a modified arm, a fist remodeled to adapt it to a special end. The energy for the action of such simple tools is supplied directly by the operator, without 'undergoing any fundamental modification on its way to the point of application. Later came levers, engines of war, and various instruments of more complicated character. Here the energy is in most cases still derived from the primitive source, the human body, but its factors undergo various changes, as in the lever, which, by lengthening the path of travel of the point of application, secures a proportionate gain in the mechanical power available—or in the crossbow, which stores up in the form of elastic strain the work done by the muscles of the arm. This pent up energy, when suddenly released by the action of the trigger, speeds the deadly missile at the foe. The bowman, having in a separate act charged his weapon with the strength of his arm, is, in the second stage of the process, free to give his whole attention to the aim. But man early found means to supplement the limited powers of his body from more lavish sources —the wind, the running stream, were pressed into his service. Then came explosives, and last of all the patient steam engine. And now becomes apparent a new feature. The new servant does more than merely replace the hand, the arm, or the feet that carry us from place to place. The inventor has, as it were, breathed into his creature a part of his own sentient soul. In orderly sequence, and with a precision that defies imitation by human hands, a legion of tireless engines in the factories throughout our land perform innumerable tasks that seem to require the guidance of a reasoning mind. The co-ordination centers of the inventor's brain have, as it were, been implanted in the machine. Nor is this all. Such purely mental a task as numerical computation is now intrusted, with great saving of time and brain-fatigue, to the mechanical calculator. Indeed, a machine has been built, which, when given the premises of a problem, will, by purely mechanical manipulation, complete the argument and set forth the logical conclusion. This “logical machine,” it is true, is at the present time but a scientific curiosity and perhaps will always remain so. Coming right down to current events, a most instructive and interesting case is presented to us in the Doutre aeroplane stabilizer recently described in our columns. The action of this apparatus displays all the characteristic features of the “sensory motor circuit” of psychology. Throughout all the interactions of the individual with the external world there runs a cycle. The first link in the chain is, as a rule, a stimulus from outside, causing a “sense impression” II some one or other of Our organs of special sense, such as the eye, the ear, or the tactile papilllE of the skin. Occasionally an “internal sense” such as our sense of orientation or equilibration may take the place of our consciousness of things without. In the last stage the cycle returns again to the external world, the action being now reversed, the organism reacting upon its environments. Intermediate between these two stages there is necessarily a connecting process, which may be intensely complicated, involving all the intricacy of a long chain of mental operations; in other cases the connection is at least seemingly simple. The sensory motor circuit appears most clearly in so-called reflex actions, for here the successive steps occur in immediate sequence. Thus a sudden loud report produces an instant quiver of the eye-lid; if through some accident the balance of our body is upset, reflex action, through the medium of our sense of equilibrium, located in the semi-circular canals of the inner ear, immediately calls out a righting motion in the requisite muscles. Consciousness does not necessarily enter into these effects, which, indeed, continue during the lighter stages of anaesthesia, but, as has already been indicated, conscious action is subject to the same cycle. This is obvious enough when the reaction follows close upon the stimulus, as, for instance, when the sight of some desirable object induces us to put forth our hand and seize it. But in the great majority of cases, in the infinite variety of our daily activities, the reaction is “delayed” and many complicated steps of mental and emotional experience intervene between the data furnished by our senses and the action based upon them. But however complex these data may be, involving often the entire previous history of the individual; however intricate the maze through which the mind weaves its thread from the entrance to the soul, a sense perception, to the final goal, the reaction upon the environment: the same sensory motor circuit is discernible throughout. For all the contents of our mind are ultimately referable to sense impressions. The Doutre stabilizer is equipped with an anemometer plate which responds to variations in pressure, thus, as it were, informing the apparatus of external conditions, just as our eye, our ear, .our sense of touch, keep us informed of the state of the world around us. More than this, by a suitable mechanical connection, the stimulus thus applied to the anemometer, by relay action, sets freea store of energy which actuates an auxiliary motor. This reacts upon the environment in such a way as to preserve the aeroplane from accident. Furthermore, the Doutre stabilizer comprises an element which is the exact counterpart of some of our internal senses. The apparatus reacts not only to changes in external conditions, but also to changes of its own speed. A number of gliding weights are partially free to move relatively to the body of the aeroplane. According to the laws of dynamics, they will do so, owing to their inertia, as soon as the aeroplane suffers an acceleration. The relative motion of the gliding weights with reference to the body of the aeroplane is made to actuate the auxiliary motor, and again we have an exact counterpart of reflex action, designed to maintain the “life” of the machine. Had the inventor set to work with the deliberate intention of preparing a mechanical model illustrating reflex action, he could hardly have produced a more perfect example than is presented to us in the Doutre stabilizer. THE necessity for technical men and scientific methods in the administration of the modern city is one of the most impressive lessons to be derived from the Budget Exhibit now being held in the city of New York . for the information and instruction of its taxpayers. Taking place in October at a time when the annual discussion of the city's appropriations for the ensuing year is in progress, this exhibition supplies a full and illustrated record of the activities of the municipality. Like any large private corporation, a city requires efficiency of management and systematic cost accounting just as if it were concerned with manufacturing or transportation; but on account of political conditions, charter and other legislation, and, even more largely, lack of interest and dense ignorance on the part of the citizen stockholders, municipal efficiency and economy are more difficult of realization. However, they are the keynotes of all practical municipal administration no less than of the successful conduct of industrial operations, and to the interested taxpayer in such a ' city as New York they figure prominently at the time of the adoption of the annual budget by the Board of Estimate. To this body must come the heads of all the city departments, with their requests for appropriations for the ensuing year properly analyzed and classified, and with a record of work accomplished under previous appropriations. To secure the appropriations asked for, the department heads must convince the Board of Estimate and the taxpayers of the city that their estimates are reasonable and the record of their work such as to warrant the desired appropriation, or as much thereof as the best interests of the city will permit. To get the greatest publicity for these different departmental statements, which in 1910 included the eighteen hundred items that went to make up a $174,000,000 budget, the city of New York for two years past has hired an unoccupied mercantile building on Broadway, where are displayed such charts, diagrams, photographs, and appropriate objects as best illustrate the needs and work of each department, bureau or office. In many cases, such as departments of law and finance, the exhibit is merely statistical or a summary; but in others there are displayed photographs, specimens, apparatus, or machinery which show the application of modern science and engineering to municipal problems and conditions, and the resulting increase in efficiency and economy by the adoption of recent inventions and improved scientific methods. For example, child hygiene, and food and milk inspection are items calling this year for largely increased estimates by the Health Department. At the Budget Exhibit can be seen charts showing what has already been accomplished along these lines together with statements of what is desired. To give point to this there are shown actual photographs contrasting wholesome conditions with those which give rise to disease; also the various physicians, nurses, inspectors and other officials of the department are portrayed at work in schools, tenements, milk stations, and even at the farms. To support the demand of the Fire Commissioner for appropriations for new motor apparatus, there may be seen at the exhibition a high-power gasoline pumping engine, that has recently passed the rigorous requirements of the department engineers, and a modern motor hose wagon temporarily withdrawn from active service. Interesting as these are as engineering novelties, it is in connection with their surprising economy that they find place in the budget exhibit, eliminating as they do the more expensive fire horse, an honored specimen of which is stabled hardby the new apparatus. The best methods of fire-proof construction and fire prevention, soon to be enforced by a new Bureau of Fire Prevention, are also shown. The Department of Docks and Ferries by plans, photographs and models shows its comprehensive schemes for developing and increasing the water front to provide much needed facilities for commerce. The Department of Water Supply, Gas and Electricity shows the various devices used in the distribution. and measurement of water, with some interesting relief maps by which the history of water supply and distribution is shown from the time of the settlement of the city. The progress of the great Catskill Aqueduct is also graphically illustrated by photographs and models, and a comparison is made with previous supply systems. These few instances are but typical of the many exhibits, both graphic and practical, that make up this most interesting display; but they like others serve to emphasize that close connection between municipal economy and scientific work which is not always realized outside the ranks of municipal engineering. If the lives of the poor and particularly of infants are properly to be safeguarded the testing of milk and food must be done in the laboratory and standards adopted for the inspectors. Improved fire apparatus must be supplied, if adequate protection is to be furnished to buildings that are ever increasing in number, volume and height. New docks for the commerce of the future and to produce revenue for the city must show the best civil engineering of the day. These projects, illustrated and described, do, or should, represent the best engineering of the time. And the citizen who examines the vast budget of the city for its current expenses as well as the bonds issued for permanent improvement, must have the conclusion forced upon him that it is the engineer rather than the politician who should be primarily responsible for conducting the affairs of a great city, at least if efficiency and economy are to be secured. Even under present conditions the part played by the former is greater than many would suspect. It is the engineer, the architect, the sanitarian, the physician, the landscape gardener and other workers of applied science that make our cities. Their influence equals, if it does not surpass that of our legislators and politicians. This fact is impressed strongly upon every understanding visitor to the Budget exhibition.