Causes of the Motion of the Blood. 347 



lary circulation have not presented any remarkable change, 

 even when raising the pressure rapidly to 2, 3, 4, 6 and 

 8 atmospheres, and reciprocally. Farther, the circulation 

 has continued to preserve the same rhythm even under a 

 pressure of some centimetres (39 inches) in salamanders, 

 frogs and tadpoles. On placing in the appai'atus very 

 young rats and mice (it is well known that the mammalia, 

 during the first days of their birth, may remain some hours 

 without breathing) the circulation can be seen perfectly, in 

 vacuo. How absurd, then, is the opinion of these philoso- 

 phers who consider that, without atmospheric pressure, 

 circulation cannot go on ; but atmospheric pressure, com- 

 bined with the motions of respiration, are accessory causes 

 of the flow of the blood, as Dr. Poiseuille has shewn in 

 another memoir. 



From these experiments, he infers, that the thickness of 

 the layer of serum, the existence of which is due to the 

 affinity subsisting between the coats of the vessels and the 

 serum, a thickness which varies so remarkably from heat 

 and cold, is independent of surrounding pressure, that the 

 contractions of the heart preserve their normal rhythm, 

 whatever the pressure is. 



Several tubes of chara, placed in this apparatus, had pre- 

 sented, under a pressure, varying from 209 (7 # 8 inches) to 

 600 centimetres (236 inches) the same modes of circula- 

 tion ; and the motions of some infusorii contained in the 

 water of the chara, such as vorticelli, potiferoz, Sec, were 

 executed with the same facility as under the influence of 

 the atmosphere. 



Article IV. 



On the Connexion between Refracted and Diffracted Light. 

 By Paul Cooper, Esq. 



{From a Paper read before the Royal Society, 8th May, 1834.) 



It is remarkable, that nearly two centuries have elapsed, 

 during which, other sciences have sprung up and arrived 

 at maturity, without producing any considerable alteration 

 in the material theory of light, as it was left by its illustri- 



