ON SPONGIOPORPHYRIN. 847 



one to read off the percentages of unabsorbed light. These 

 are the percentages which are expressed by the ordinates 

 of the curves. The abscissfe of the curves are wave-lengths 

 of light, in millionths of a millimetre (lufi). 



I may now give the data upon which these curves are con- 

 structed. 



[The tables of measurements and the diagrams exhibiting 

 these results in the form of a curve are printed on the next 

 tAvo pages (pp. 348, 349), so as to enable the reader to com- 

 pare tliem without diflBculty. They should be compared with 

 tlie similar curves drawn by Professor Engelmann for 

 chEetopteriu and bonellin (this Journal, vol. 40). The size 

 and conditions adopted for the two diagrams of absorption 

 curves here figured would seem to be well adapted to serve 

 as a standard scheme, and it would be desirable to have a 

 series prepared on this model, illustrating the absorption of 

 each of the more important substances which present irre- 

 gular curves of absorption, such as haemoglobin, chlorophyll, 

 potassium permanganate, nitrous oxide gas, etc. — E. R. L.] 



