446 PROCEEDINGS OF THE SOCIETY. 



tracing the origin of the colours to this, in the diatom in question, he 

 found that the same phenomena were met with, though not so strikingly, 

 in many other diatoms, Phurosigma angulatum amongst the number. 

 He had indicated at the time how this might be applied in order to 

 estimate the thickness of the diatoms.* He thought Mr. Hartridge 

 might find it of some use to him to have an independent method avail- 

 able of tackling a problem of this nature for the purpose of comparing 

 and testing results. 



Mr. Hartridge said there was one point to which he would Hke to 

 call attention, and that was that he did not think Mr. Gordon fully 

 appreciated what he (the speaker) was trying to get at, when he 

 remarked in his letter how difficult it was to estimate the difference 

 in refraction set up by hexagonal and triagonal structure. Mr. Hart- 

 ridge said he did not propose to make any attempt to estimate the 

 shaiie of apertures : what he proposed to do was to find out what the 

 markings were, their approximate size, and various other points con- 

 nected ^\ith them. 



Mr. Hartridge thanked Mr. Rheinberg for his suggestion in regard 

 to the colours of Pleurosigma, but so far as he knew at present there 

 was no evidence of laminary structure. The series of colours obtained 

 seemed to agree much more with those one would expect from the 

 passage of diffraction spectra of increasing order than with those caused 

 by interference, as in Newton's rings. 



(Mr. Rheinberg bad since the Sleeting kindly sent Mr. Hartridge a 

 reprint of the paper on Actinocyclus Ralfsii (Journ. Quekett Micr. Club, 

 April 1913, p. 13), to which he had referred. This contains an excellent 

 account of the experimental data to be observed when mutual inter- 

 ference of spectra takes place. Mr. Hartridge recommended every one 

 interested in this subject to refer to the original paper, if not already 

 familiar with it.) 



In further illustration of his paper, Mr. Hartridge had diagrams of 

 his apparatus thrown on to the screen, fully explaining aU details of 

 construction. 



The hour growing late, and it being necessary for the President 

 (Professor Sims Woodhead) to leave, Mr. F. J. Cheshire took the Chair, 

 and a very hearty vote of thanks was proposed to Mr. Hamilton 

 Hartridge for his interesting and valuable contribution to microscopical 

 science, which vote was carried with acclamation by all present. 



Mr. E. J. Sheppard read a paper on "The Structure of the 

 Nucleus." 



In discussion on the paper, Mr. Coon said that, though not a Member 

 of the Society, he was taking advantage of his privilege as a visitor by 

 saying a few words on the subject, for it was one in which as an amateur 

 he had taken considerable interest. A few days ago when examining 

 some sections of the lily ovary at an optician's, he had been much struck 



* Journ. Quekett Micr. Club, viii. (1901) pp. 13-24. 



