99 



Mr. F. Oxley „ Mr. Parsons „ Mr. T. Powell. 



Mr. A. de S. Guimaraens Mr. Crisp „ Mr. F.H.Ward. 



Mr. E. Simpson „ Mr. Terry „ Mr.F. H. P. Hind. 



The President announced that Mr. Hainworth had been appointed auditor 

 of the accounts by the committee, and requested the appointment of 

 another gentleman to act in that capacity on behalf of the members. 



Mr. Dobson was then proposed by Mr. Curties, seconded by Mr. Cottam, 

 and elected in the usual manner. 



Mr. Frank Crisp then read a paper " On the Influence of Diffraction in 

 Microscopic Vision," the subject being well illustrated by excellent coloured 

 diagrams, and by objects and apparatus exhibited in the room, special 

 attention being called to the exhibition of Pleurosigma angulatum by Mr. 

 J. W. Stephenson with the new oil-immersion lens, and with the central 

 dioptric ray stopped out so as to produce an image formed by diffraction 

 spectra only. 



Mr. J. W. Stephenson, in reply to the President, said that Mr. Crisp had 

 so completely exhausted the subject that he hardly knew if he could add 

 anything to what had been said, except to point out that the experiment 

 which he proposed to show with P. angulatum was merely the exclusion of 

 the central dioptric beam, and that the effect of this was that the mark- 

 ings were shown as bright circular dots punched ont of a beautiful blue 

 ground. If every alternate spectrum was stopped out then hexagonal mark- 

 ings were seen. With the oil lens the angle was so large that it took in 

 spectra of the second order. 



Mr. Curties enquired if the appearance shown was to be considered as 

 the correct view of the object ? 



Mr. Stephenson said they did not know what was the correct view. 

 Mr. Ingpen said that what Mr. Crisp had brought forward as the rudi- 

 ments of this subject formed the groundwork of the knowledge of a branch 

 of microscopy which was of very great importance, and it was just in this 

 way that one should bring forward the first principles of a matter which 

 every one would agree ought to be well known, and could not be too widely 

 or thoroughly understood. And he might add that he hoped the subject 

 would be followed up not only by the members themselves, but also that 

 further instruction might be given at suitable times of the application of 

 the principles involved. As soon as the principles were explained in a 

 paper, the subject became educational, and there was then great scope for 

 explaining these applications to the members of the Club, to whom it could 

 be shown how great was the advance thus made both in the theory and 

 practice of the microscope. 



Mr. Frank Crisp briefly, by means of drawings upon the black board, 

 showed how the intersection of three sets of lines naturally produced the 

 appearance of hexagonal markings. 



The President then proposed a vote of thanks to Mr. Crisp for his 

 excellent paper, and also to Mr. Stephenson for his kindness in coming 

 down that evening to illustrate it. Carried by acclamation. 



Announcements of meetings and excursions for the ensuing month were 



