PROCEEDINGS OF THE SOCIETY. 563 



for use at the bedside, as for the use of persons who preferred to carry 

 a medium size instrument with them when travelling. 



The new mechanical stage was of somewhat novel construction, it 

 having three special features, viz. a large horizontal travel amounting to 

 ;;^ inches, a surface perfectly unobstructed, and further the two milled 

 heads, which were mounted on one spindle on the Turrell system, were 

 placed at an angle to the movements of the stage which was not usual. 



The stage was specially designed for the use of bacteriologists and 

 those who examine living objects. 



The working arrangement was effected by rackwork and pinion of 

 peculiar construction ;"a sliding bar could be used on the stage if occasion 

 required. 



Mr. Beck said he had brought with him to the Meeting a Spinthari- 

 scope, the arrangement by which Sir William Crookes demonstrated the 

 Rontgen rays emitted by radium. This was also made in the form of 

 a microscopic object, but it required to be shown in a darkened room. 

 In a room such as that in which they were meeting, where there were a 

 number of electric lights, it would be very difficult to show, but it was 

 quite easy to see at any time in a room not too brightly lighted. 



The Chairman moved a vote of thanks to the three gentlemen to 

 whom the Society was indebted for their interesting exhibitions, all of 

 which presented distinct improvements in the directions which the 

 makers had in view. 



The thanks of the Meeting were then unanimously voted. 



The Chairman said the first paper on the Agenda was by Lord 

 Rayleigh, " On the Theory of Optical Images, with special reference to 

 the" Microscope." Lord Rayleigh had written to excuse himself from 

 being present, and mentioned that this paper was to be regarded as supple- 

 mentary to a paper of his which appeared in 1896 in the Philosophical 

 Magazine, and at his special request the Council had agreed that the 

 original paper should appear in the Journal along with the supplement, 

 so that the Fellows may have the whole argument before them. 



Dr. Hebb then read a portion of this communication, the rest being 

 taken as read. 



Mr. Vezey said the paper contributed by Lord Rayleigh was a most 

 valuable one, and he felt sure the Fellows would agree that his Lordship 

 had paid a compliment to the Society by making it the medium of his 

 communication. Lord Rayleigh had also kindly permitted the republi- 

 cation of an earlier paper of his on the Microscope, and this would appear 

 in the same number of the Society's Journal as his paper just read by 

 the Secretary, and the value of the latter would be greatly increased 

 thereby. The Society was greatly indebted to Lord Rayleigh. 



The thanks of the Society were then, on the motion of the President, 

 cordially voted to Lord Rayleigh for his paper. 



Dr. H. Siedentopf read his paper, " On the Rendering Visible of 

 Ultra-Microscopic Particles, and of Ultra-Microscopic Bacteria," the 



