An aperture in the wall of a building, for the admission of light and air. Modern windows are almost uniformly furnished with glazed frames, that open and close, besides shutters and blinds, by which the admission of the light and air may be easily regulated at pleasure. - See the Article Glazing. In this place we propose to notice several improvements which have of late years been made in the mechanical construction of windows.

It has frequently been a subject of complaint, that our public edifices are either insufficiently provided with the means of ventilation, or the arrangements for that purpose are very inconvenient. The oldest mode with which we are acquainted is that of casements hung upon hinges, and fastened by a latch. A later and more improved method was to hang the casements so as to swing upon centre pivots; the opening and shutting of these casements by pulleys and lines is always accompanied with noise, and they afford no defence from a shower of rain, nor to the prejudicial effects of the cold air descending on the heads of the persons assembled near to the windows. Another mode, lately introduced, is to cut out of the windows a space to receive the half of a glazed hopper, which is attached to the window, projecting inwards, having a flap on the top, lying horizontally, and opening upwards. These hoppers are extremely unsightly in themselves, but are rendered still more so by the dust which lodges on them; which dust is blown into the building when the flap is opened for the admission of air.

To remedy these inconveniences, Messrs. W. and D. Baily some years ago invented the arrangement delineated in the preceding page; by which a ready mode of action on the upper part of the window is obtained by very simple machinery, while the symmetry of the window is preserved. Fig. 1 gives a front inside view of a window, with the apparatus attached, and Jig. 2 is a side view of the same; a shows the flap of the window open; b b a bar to which the base of the flap is fixed, and on which it turns; e a lever, having one end fastened to the extremity of the bar b, and furnished at the other end with an eye, which receives the pin or stud d; this stud is fixed on the vertical rod e, which terminates below in a rack f, and is secured in an upright position by the loops or guides gg. through which it passes; h is a lan-thorn pinion of two teeth, which when turned round by means of the winch i takes into the notches of the rack, and consequently draws down the rod e or raises it, according to the direction in which the winch is turned In the first case, the stud d draws the lever down, and consequently opens the window; in the latter the stud is raised, and with it the lever, which shuts the window It may be proper to observe, that in case of the upper part of the window being square, and not having any mullions, it will be found necessary (to prevent the entrance of the air at the side of the casement, when it opens) to have a frame with two angular sides attached to the windows, and these sides must have a small return rebate for the casement to fall against when it is fully opened, which will prevent any inconvenience arising from the form of the window.

Fig. 1.

Fig. 2.

Servants and others employed in the cleaning and repairing of such windows in general provide so indifferently for their security, while employed on the outside, that numerous accidents have occurred, - some, of the most deplorable nature. The construction of the sash windows that we have now to notice, will not only effectually prevent these accidents, but will remain a permanent convenience to the house in which they may be adopted. In appearance these sashes resemble those of the common kind, and the upper and lower sash may be moved up and down in a similar manner. The outside of the sash may also be turned into the room, so that it may be easily painted, glazed, or cleaned, by a person standing within the room, without the necessity of removing the slips or headings; by doing which the glass is frequently broken, and the beads lost, left loose, or dismatched, and a considerable expense incurred. The frame of the window is fitted with grooves, weights, and pulleys, in the usual manner; the fillets on the sash are not made in the same piece with the sash frame, but fastened thereto by pivots, about the middle of the sash; upon these pivots the sash is turned round at pleasure, so as to get at the outside without disturbing the fillets or grooves.

When the sash is placed vertically (as the lower one in the figure) a spring catch on each side of it shoots into, and take hold of the sliding fillets; so that in this case the sash slides up or down in the usual manner, but can be immediately released, and turned inside-out by pushing back the springs, and at the same time pulling the sash inwards. This invention originated with Mr. Marshall, who communicated it to the Society of Arts; but the invention, with some unimportant modifications, was subsequently satented by Mr. Tucly, probably from ignorance of Mr. Marshall's prior claims, we notice this fact, as windows of this kind are sometimes called Marshall's, and at others Tucly's patent revolving windows. On account of the additional expense from six to twelve shillings) of these windows above the ordinary kind, the builders do not encourage them; but this additional expense is scarcely worthy of notice by a private individual in building, when the important advantages It confers are taken into account.

To keep the sashes of ordinary windows at equal distances from the sides, so that they may not be impeded in drawing up and down, (as is often the case, on account of the sash swinging as it is suspended by thetop,) Mr. Woolwich has proposed the simple appendage represented in the annexed cut. Fig. 1 is a plate of iron two inches long by one inch wide; to the lower part of which is fixed a spring b, that carries a roller at its upper end, and at c c are two holes vol. II.