132 Dr. C. A. MacMunn. On the Colouring-matters [Apr. 5, 



In § 5 is studied the case of induced currents. Since any disturb- 

 ance in the field (however arbitrary) can be expressed, as regards the 

 time, by a series of simple harmonic terms, it is sufficient to consider 

 the case when the variations in the inducing system follow the simple 

 harmonic law. This case has, moreover, acquired a special interest 

 since the invention of the telephone. The two extreme cases, where 

 the period of the variation in the field is very large or very small in 

 comparison with the time of decay of free currents in the sphere, are 

 discussed in some detail. 



In § 6 the case of a thin spherical shell is briefly examined. 



I next proceed to investigate what modifications must be introduced 

 into the methods and the results of the preceding sections when the 

 substance of the sphere is susceptible of magnetisation. This occupies 

 §§7, 8, 9,10. _ 



In the remaining sections of the paper I investigate the solution of 

 our fundamental equations, taking account of the finite value of v. 

 The corrections to our former results are of most interest in the 

 solutions of the second type. Although the preceding theory, based 

 on the assumption v— oo , is sufficient for all purposes of compa- 

 rison with experiment, there are certain processes of (at all events) 

 theoretical interest of which it fails altogether to give an account, 

 viz., all those cases in which any change in the superficial electrifica- 

 tion of the sphere takes place. For the expression of these the 

 solutions of the second type are appropriate. There is no difficulty in 

 w r orking out the requisite formula?, but in the application to the case 

 of free motion a difficulty of interpretation arises, which is noticed in 

 the proper place. 



III. " Observations on the Colouring-matters of the so-called 

 Bile of Invertebrates, on those of the Bile of Vertebrates, 

 and on some unusual Urine Pigments, &c." By Charles A. 

 MacMunn, B.A., M.D. Communicated by Dr. M. FOSTER, 

 Sec. R.S. Received March 8, 1883. 



(Abstract.) 



In this paper the result of a systematic examination of the bile and 

 various extracts of the livers of Mollusca and Arthropoda, and of the 

 pyloric or radial caeca and other appendages of the digestive system 

 of Echinodermata is described. The universal distribution of one 

 colouring-matter, which by appropriate experiments is shown to be a 

 chlorophyll pigment, is proved. It occurs in the above organs and can 

 be detected in the bile of specimens of Helix after a six months' fast ; 



