Page:Proceedings of the Royal Society of London Vol 1.djvu/152

Rh more particularly that which passes through blue glass.‘ This, we are told, may be separated by the prism into seven distinct portions, nearly equal in magnitude: the two ﬁrst are red, the third yellowish green, the fourth green, the ﬁfth blue, the sixth bluish violet, and the seventh violet. This division, it seems, agrees perfectly with that of the light reﬂected by a plate of air ﬁn] part of an inch in thick- ness: and hence we may infer the extreme minuteness of the par- ticles of light.

The sixth and last section describes an experiment on certain dark rays, which were ﬁrst noticed by Ritter, and relates to the exis- tence of solar rays accompanying light, but cognizable only by their- chemical effects. This fact our author has conﬁrmed by observing the effect of the reﬂection of these invisible solar rays from a thin plate of air capable of producing the well-known rings of colours. This image he threw on paper dipped in a solution of nitrate of silver, and in less than an hour he distinctly perceived portions of three dark rings, nearly of the same dimensions, but manifestly dif- ferent from the coloured rings. This seems to coincide with Dr. Herschel’s late discovery of rays of invisible heat; but our author doubts whether we are yet possessed of thermometers of sufﬁcient delicacy to place implicit conﬁdence in the experiments hitherto made on these rays by means of that instrument.

Since the communication of his former paper on that subject, the

author has collected further illustrations respecting the connexion between the disposition of the blood-vessels and the actions of the muscles. His ﬁrst observations relate to the spermatic and inter- costal arteries, and those.of the diaphragm in men ; which, he ﬁnds, are distributed 'in a different manner from those of the ordinary muscles. Compared with the distribution of the coronary arteries, it is found that the latter are much more subdivided or arboreseent than any other set, and that accordingly these supply the heart,—a muscle whose actions we know are more rapid than those of any other part of the muscular system.

It is hence inferred, that any impediment to the accustomed course of the blood, ﬂowing through muscles, induces a corresponding diminution in their power of action; and that wherever we ﬁnd cylindrical arteries emitting few lateral branches, we may conclude that they appertain to muscles of slow but in general of long-continued motion. Of this, instances are given in the human eye, the swimming-bladder of ﬁshes, the intestinum ileum of the Cavia Aguti, and various animals of the amphibious class. The better to illustrate his observations, the author has added ﬁgures of the swimming-bladder of the tench, and of the ileum of the Aguti.