556 PROCEEDINGS OF THE SOCIETY. 



making a mechanical stage without plates, so that the object might 

 rest at once upon the most solid part of the stage itself. The device 

 which he now exhibited fulfilled this requirement, the slide being 

 held in its place by a clip, to which motion in two directions could 

 be given by means of milled heads, whilst the whole rested upon the 

 glass stage-plate perfectly free from any flexure. Moreover, if the 

 mechanical movement was not wanted to be used, it was readily 

 removable, leaving the stage clear. Another small improvement had 

 been made, by means of which the mirror could be placed in a fixed 

 position, so as to get variations in the inclination of the light from 

 the fixed mirror when the radial movement was used. 



The President thought that the ease with which the mechanical 

 movement could be removed from the stage made Mr. Mayall's 

 modification a most excellent feature. 



Mr. G. D. Hirst's communication was read referring to the 

 report in the Journal of the Eoyal Society of New South Wales (ante, 

 Vol. V. 1885, p. 1077), attributing to him the view that a highly 

 refractive mounting medium enabled objectives of small aperture to 

 compete in resolution with wide-angled oil-immersion objectives. 

 Mr, Hirst explained that the report was unfortunately worded so as 

 to convey a totally erroneous impression of what he claimed, which 

 was only that the highly refractive medium would render difficult 

 test diatoms so easy to a good high-angled water lens, that the 

 superiority of the oil-immersion objective will not be apparent, except 

 under the very deepest eye-piecing. 



Dr. Hudson's request was read for specimens of BracMonus 

 pala, which he was unable to procure in his own locality, and which 

 he required for the purpose of illustration in his ' Eotifera.' 



Mr. C. D. Ahrens's paper " On a new Polarizing Prism " was read 

 (supra, p. 397). Mr. Crisp said that, having asked the opinion of 

 Professor Silvanus P. Thompson as to the merits of the prism, he 

 had received from him the following reply : — " My opinion of 

 Ahrens's new prism is that for use as a polarizer it is absolutely 

 unrivalled. Flat ends, wide angle, absence of distortion, absence of 

 troublesome coloured fringes, all go in its favour. The line that 

 marks the junction of the sections is all but imperceptible, and never 

 troubles the clearness of the field, as used for this purpose. For use 

 as an analyzer I am not so clear about the prism ; but even so it 

 works very well. Take it all round, I consider it the best polarizing 

 prism that has yet been devised." 



Dr- Sternberg's paper " On Micrococcus Pasteuri" was read (supra, 

 p. 391), in which he called attention to the characters which dis- 

 tinguish it in a very definite manner from the microbe of fowl-cholera. 



