Hemispherical glass roofs

2048. The last and most important era is marked by the fortunate discovery of the late Sir G. Mackenzie, in 1815, 'that the form of glass roofs best calculated for the admission of the sun's rays is a hemispherical figure.' This may be considered as the ultimatum in regard to the principle and perfection of form; and it has given rise to many beautiful curvilinear structures: