464 Royal Society : Prof. Moseley on the 



that no air could be thus extricated, the author is induced to believe 

 that the quantity of air contained in the blood is variable : and he 

 has found this air to consist solely of carbonic acid gas. It would 

 also appear, from the experiments detailed in this paper, that a por- 

 tion of oxygen exists in the blood, not capable of being extracted 

 by the air-pump, yet capable of entering into combination with ni- 

 trous gas ; and existing in largest proportion in arterial blood. The 

 absorption of oxygen by blood is attended with an increase of tem- 

 perature. 



The experiments of the author tend to show that the lungs are 

 absorbing and secreting, and perhaps also inhaUng organs, and that 

 their peculiar function is to introduce oxygen into the blood and 

 separate carbonic acid from the blood : and they favour the idea that 

 animal heat is owing, first, to the fixation or condensation of oxygen 

 in the blood in the lungs during its conversion from venous to arte- 

 rial ; and secondly, to the combinations into which it enters in the 

 circulation in connexion with the diff^erent secretions and changes 

 essential to animal life. 



" On the Geometrical Forms of Turbinated and Discoid Shells." 

 By the Rev. H. Moseley, Professor of Natural Philosophy and As- 

 tronomy in King's College, London. Communicated by Thomas Bell, 

 Esq., F.R.S. 



This paper is occupied by an investigation of certain mathemati- 

 cal principles which the author considers as governing the formation 

 of turbinated and discoid shells. According to these views, all such 

 shells may be conceived to be generated by the revolution about a 

 fixed axis of the perimeter of a geometrical figure, which, remaining 

 always similar to itself, increases continually its dimensions. The 

 spiral lines which are observable on the opercula of certain classes 

 of shells, taken in connexion with the well-known properties of the 

 logarithmic or equiangular spiral, appear to have suggested the idea, 

 that not only the boundary of the operculum, which measures the 

 sectional expansion of a shell, but also the spiral lines, which in 

 general are well marked both externally and internally in the shell 

 itself, are curves of this nature. 



From an examination of the spirals marked on opercula, it appears 

 that the increase of their substance takes place on one margin only; 

 the other margin still retaining the spiral form, and acquiring an in- 

 crease of length by successive additions in the direction of the curve. 

 As in the logarithmic spiral the distances of successive spires, mea- 

 sured on the same radius vector produced from the pole, from 

 each other, are respectively in geometrical progression, if similar 

 distances between the successive whorls on the opercula of shells be 

 found to observe the same law, it will follow that these whorls must 

 have a similar form; and that such is the case, the author shows by a 

 variety of numerical results obtained by careful measurements on 

 three diff'erent opercula of shells of the order Turbo. That such is 

 the law of nature in the formation of this class of shells is rendered 

 probable by the instances adduced by the author, in which a con- 

 formity to this law is found to exist. 



