491 



The Hon. Secretary gave notice that in the course of concluding 

 a new lease wit li their landlords, the I loyal Society of Medicine, 

 it had been found necessary to alter the days of meeting from the 

 first and third Fridays to the second and fourth Tuesday-. The 

 next ordinary meeting, to be held Friday, May 7th, would be 

 made special for the purpose of altering Rules 1 and 9 to accord 

 with the new arrangement. The new lease would take effect 

 from June next. 



Mr. C. Lees Curties, F.R.M.S., of Messrs. Baker, gave an 

 exhibition of some of the different illuminants for the microscope. 

 He said that the subject was a very large one, and it would be 

 quite easy to cover all the available table-space with the different 

 forms of apparatus designed from time to time to this end. He 

 proposed, however, to confine himself to lamps, but, owing to 

 the limited number of plugs available, could only exhibit three 

 electric lamps at a time. Be was showing >ome paraffin and 

 electric lamps in comparison. 



First as i" the evenness of illumination of the field. 



Second : Intensity. 



Third : Colour and the advantage "t' screens. 



All the six microscopes shown had /..-in. oil-immersion objecth es 

 of N.A. l-:>0. eyepieces No. Land Abbe condensers (not achro- 

 matic). The specimen shown was Pleurosigma angzdatum. 



The first microscope was illuminated by a |-in.-wick paraffin 

 lamp, edge of flame, and the diatom was perfectly resolved ; 

 but the sides of the held were not evenly illuminated. 



The second stand had the same kind of lamp, but with the 

 addition of the small illuminating lens lately suggested by 

 Mr. II. M. Nelson. The resolution was as perfect as in No. 1, 

 and the field was evenly lighted. 



The third microscope also had a |-in.-wick lamp as illuminant, 

 but a green glass screen was employed. The extra sharpness 

 and improved definition well illustrated the advantage of the 

 use of suitable screens for such work. Microscope No 4 had 

 similar optical parts and specimen, and was to have been 

 illuminated by a Nernst electric, but which, owing to failure 

 of the resistance, was not available. When such an illuminant 

 is employed, owing to the narrow filament, only a small part of 

 the field is lighted. By employing the ground-glass screen 

 supplied with the lamp, even illumination may be obtained, but 



