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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 16 4goth 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 Hitter, 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. 



Continuation of an Account of a peculiar Arrangement in the Arteries 

 distributed on the Muscles of slow-moving Animals, fyc. In a Letter 

 from Mr. Anthony Carlisle to John Symmons, Esq. F.R.S. Read 

 December 8, 1803. [Phil. Trans. 1804, p. 17.] 



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 arborescent 

 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 dimi- 

 nution in their power of action ; and that wherever we find cylin- 

 drical 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 swim- 

 ming-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. 



