These three varieties of the Romana rustica are marked off from one another more distinctly than is the case with, say the Romance dialects of Italy; they do not interpenetrate one another, but where the one ends the other begins.
Leonardo certainly was in relation with some persons belonging to that circle when he published in 1220 another more extensive work, De practica geometriae, which he dedicated to the imperial astronomer Dominicus Hispanus.
In his Memoire sur le refraction des corps solides (1741) he was the first to give a theoretical explanation of the phenomenon which is witnessed when a body passes from one fluid to another more dense in a direction not perpendicular to the surface which separates the two fluids.
To oppose them the Confederates, limited as they were for means, managed to construct various ironclads, and to improvise a considerable fleet of minor vessels, and, though a fighting navy never assembled under a Confederate flag-officer, the Southern warships found another more damaging and more profitable scope for their activity.
The three existing genera, usually spoken of as members of the Gnetales, differ from one another more than is consistent with their inclusion in a single family; we may therefore better express their diverse characters by regarding them as types of three separate families-0) Ephedroideae, genus Ephedra; (2) Welwitschioideae, genus Welwitschia; (3) Gnetoideae, genus Gnetum.
With the exception of Australasia, the family has a cosmopolitan distribution; and its numerous species resemble one another more or less closely in general external characters.