Calyx campanulatus, 5-dentatus, æstivatione imbricatâ, pube stellatâ tomentosus, bracteolatus. Petala 5, hypogyna, unguiculata, æstivatione convoluta, callo inter unguem et laminam. Stamina in toro longo filiformi insidentia. Antheræ 15, sessiles, in cyatho capituliformi, apice tantum pervio, obsoletè 5-dentato connatæ, extrorsæ, biloculares, loculis divaricatis intricatis, longitudinaliter dehiscentibus. Pollen sphæricum glabrum. Ovarium sessile, intrà cyathum antheriferum, ovatum, glabrum, 5-angulare, 5-loculare, loculis dispermis. Ovula margini loculorum unum super alterum affixa, superiore basi concavo in inferiorem incumbente. Stigma 5-lobum, simplicissimum, sessile. Capsula stipitata, lignosa, obovata, 5-angularis, 5-locularis, loculicidò 5-valvis, axi nullo. Semina cuique loculo duo basi alata.——Arbor (Chinæ) foliis alternis exstipulatis, racemis terminalibus compositis, floribus albis. 1. Reevesia thyrsoidea. _Habitat_ in China (v. s. sp. in Herb. et iconem in Bibliotheca Soc. Hort.) [p113] ASTRONOMICAL AND NAUTICAL COLLECTIONS. i. _Elementary View of the_ UNDULATORY _Theory of_ LIGHT. _By_ Mr. FRESNEL. [Continued from the last Number.] I shall not undertake to explain here in detail the reasons and the calculations which lead to the general formulas that I have employed to determine the position of the fringes and the intensity of the inflected rays: but I think it right to give at least a distinct idea of the principles on which this theory rests, and particularly of the principle of _interference_, which explains the mutual action of the rays of light on each other. The name of interference was given by Dr. YOUNG to the law which he discovered, and of which he has made so many ingenious applications.