It may be worth noticing that a regular polyhedron--the elements of which exert a force not varying at all with the distance, and in which the absolute energy of the centre is precisely equal to that of the vertices combined--gives a resulting force following the law of gravitation, at any distance compared with which its own dimensions can be neglected; and within this distance the force will change its sign under the same conditions of direction as specified in the previous case. But, as the intensity of this force will change with the size of the molecule, it does not appear that a system of this kind would be admissible, since, besides the periodical change due to its own internal vibration, it would probably be changed in size, or even in shape, which would be worse, by compression or expansion of the mass; which would be the more likely, as the molecules could approach much nearer than in the former supposition. The law followed by gravitation also seems to be almost or quite necessary for forces radiating from a point. The author's theory seems, on the whole, extremely plausible. That each element of matter exerts a force following the law of gravitation, is almost demonstrable _à priori_; that the elements are mere points, will also generally be admitted; that some of the actions should be repulsive, is obviously necessary; that each molecule is composed of a definite number of atoms, is suggested by chemical laws; and the polyhedric forms seem certainly the most reasonable, though crystalline forms would indicate that others may be occasionally found. The possibility of the construction of irregular molecules out of elements of unequal powers seems, by the way, to be worth examining. Further developments of the theory may have recently been made; of course, the author does not claim in this work to have laid down more than its first principles. At present, it seems, to say the least, to furnish the best basis for the mathematical investigation of the internal constitution of matter that has been suggested, and such investigations would be almost certain to lead to valuable results, whether confirmatory or otherwise. THE HOLY-WEEK OF 1869 IN HAVANA. PALM-SUNDAY. THE TENEBRÆ. MAUNDY-THURSDAY.