This section is from the book "The Gardener's Monthly And Horticulturist V20", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
We do not quite understand the following, which we rind in the Polytechnic Review. Illustrations would perhaps he required to make it plain. But as there may be something, if properly understood in the principle, of value to our greenhouse people, we give it in the hope that it may bring out further information :
"We lately saw a defectively glazed glass roof under treatment toward restorating broken panes and stopping leaks. Counted by the acre, the surface of such glazing is enormous in the city of St. Louis, and would be increased were the immunity from leakage and breakage nearly assured. The system of glazing used on the roof of the Royal Aquarium, London, is held up as a model of this sort of protection and convenience; it •consists of a series of zinc bars of pot-hook section, with a return bend, the bars being screwed on the purlins. The top is simply a pot-hook or hanger section, at the bottom of the same section reversed. The glass rests in the groove of the lower bars and back groove of the intermediate upper one, in which it has full vertical play. The panes of glass lap each other; and the theory is, that no water can find its way inside the building covered by a roof glazed on this principle. The advantages of this system appear to be the diminution of breakage of glass from vibration, and expansion and contraction and other causes due to rigid fixing in the ordinary system, and the facility with which glass can be fixed or a damaged pane removed and replaced.
The grooves carrying off water from the inside as well as from the outside is of course another advantage, for unless the roof be a very flat angle, indeed, water will not leave the glass, but will run down into the outside groove. Condensed water and vapors are, therefore, thus well got rid of".