Although the ordinary double hung window has been found superior, on the whole, to any other device for furnishing light and ventilation, it has two defects, one of which becomes quite serious in the upper stories of buildings. These defects are that the outside of the glass is not easily cleaned, and only one-half of the opening can be utilized for ventilation at a time (unless there is a pocket above the head). Several devices have been patented for overcoming these objections, the most successful of which appears to the author to be those which permit each sash to revolve on a centre, thus permitting the outside of the glass to be easily cleaned from the inside, and also affording greater ventilation in warm weather.

Fig. 106.   Bolles' Patent Revolving Sash.

Fig. 106. - Bolles' Patent Revolving Sash.

Bolles' Patent Revolving Sash. - Of these patented windows, that which appears to have proved the most practicable, or which, at least, has found the greatest favor, is known as the Bolles' Patent Revolving Sash.

This window has been quite extensively used in New York and neighboring States with very satisfactory results.

The revolving arrangement can be fitted to any double hung window frame, as it affects only the sash. Each sash is pivoted at the centre of gravity of the sides, the sash being made narrower than the width between the stop beads and pivoted to a separate convex strip, which slides up and down in the frame, in precisely the same way as an ordinary window, the sash chain or cord being attached to the strips, as shown in Fig. 106. The inner surface of the strips is convex, and accurately fits into a corresponding concave groove in the sides of the sash, making a perfectly water-tight joint. The back of the sliding strips are pressed against the pulley stile by specially designed expansion pins, fitted with springs, and the pivots are also fitted with springs which hold the sash and sliding strips firmly against each other, no matter in what position the sash may be placed.

It is claimed that by means of the expansion pins, above described, the sashes are held as firmly and run as smoothly as in the old style window and are equally as tight. To turn either sash - reverse it, or place it in a slanting or horizontal position - all that is necessary is to push the bottom rail outward, the binding action of the springs being sufficient to hold the sash in any desired position. The sliding strips (preferably of straight grain white pine), may be made at the mill furnishing the sash, or can be procured from the Bolles' Revolving Co., who also furnish all of the necessary fittings and complete working plans for shaping the stiles and applying the fittings. The side pulleys should be placed as high as possible (overhead pulleys are preferred). The cord and weight are the same as in the ordinary window; parting strip to extend 13/16-inch. This device is also used on transoms and large non-sliding sash. The mechanism of this sash and its operation is shown in Fig. 106.