538 PROCEEDINGS OF THE 



conference, which had been much hampered by the political 

 unrest, hurriedly broke up. The Chairman tendered the Club's 

 thanks to Mr. Bousselet for his report, and congratulated him on 

 his safe return. 



A paper by Mr. A. A. C. Eliot Merlin, F.R.M.S., was read (in 

 part) on " The Minimum Visible." It commenced : " I have 

 read with great interest and profit our President's address on 

 1 Organisms and Origins.' The subject is one that must fascinate 

 every microscopist, whatever his line of research. In the address 

 the point was raised respecting the minimum visible, it being 

 stated that ' it seems impossible to obtain any precise information 

 as to the size of the smallest particles that can be seen with the 

 microscope.' Now, setting aside the ultra-microscope, as our 

 knowledge is very exact and definite indeed on this subject, it 

 may prove of interest to deal with the question at some length. 

 As a matter of fact, when a particle properly illuminated is just 

 visible with a given objective, if the aperture be cut down by 

 means of an iris diaphragm, placed above the back lens, so that 

 the particle just ceases to be visible, and the N.A. to which the 

 objective has been reduced is measured, then the dimensions of 

 the particle can be exactly ascertained from the antipoint table 

 published by Mr. Nelson in the Journal of the Royal Microscopical 

 Society. This antipoint table should prove invaluable when 

 accurate and minute measurements are necessary." 



A recent paper by Mr. N. E. Brown, A.L.S., " Some Notes on 

 the Structure of Diatoms," was referred to, in which Mr. Brown 

 stated that he had seen pores on the surface of certain diatoms 

 which he estimated at 1/200, 000th of an inch in diameter. Mr. 

 Merlin, examining some of the diatoms under a very perfect 

 ^ apochromat, N.A. 1'4, employed with a magnification of 

 4,200, readily distinguished these pores, but in them so resolved 

 believed he immediately recognised Dr. Boyston Pigott's " dark 

 eidolic dots of interference." 



In speaking on the subject of Mr. Merlin's paper, Mr. 

 N. E. Brown said : " If I understand Mr. Merlin correctly, the 

 two points in it which call for any remark from myself are 

 that the structures I have conceived to be pores were discovered 

 by Dr. Boyston Pigott many years ago, and considered by him 

 due to interference. I much regret that I have not read Dr. 

 Boyston Pigott's paper, or I should have referred to it in my 





