798 PROCEEDINGS OF THE SOCIETY. 



MEETING 



Held on the 17th of November, 1909, at 20 Hanover Square, W. 

 F. J. Cheshire, Esq., Vice-President, in the Chair. 



The Minutes of the Meeting of the 20th of October were read and 

 confirmed, and were signed by the Chairman. 



The following Donation was announced : — 



From 

 Andrew Pritchard, A History of Infusoria, including the Des-j ^. -^ j Ttf ar fc s 

 rnidiacese and Diatornacese. 4th ed. (8vo, London, 1861) .. / 



With reference to the copy of Infusoria, DesmidiacesB, and Diatomacese 

 presented by Mr. Marks, Dr. Hebb said they were very glad to get 

 this, as though they formerly had it in their library upstairs, it had been 

 borrowed by someone and had never been returned. 



On the motion of the Chairman, a special vote of thanks was given to 

 Mr. Marks for his valuable donation. 



Mr. C. Beck exhibited and described a new form of speculum lamp 

 devised by Mr. J. W. Gordon, which was a modification of the lamp ex- 

 hibited at the last Meeting. It was mounted on a base having a raising 

 motion. The light was furnished by an electric lamp, and was concen- 

 trated upon the surface of the end of a glass rod, the structure of the 

 filament of the lamp being entirely broken up by internal reflection, so 

 that a mass of homogeneous light was produced, coining out of the rod 

 at an angle of not more than 15° or 20°. For critical illumination, the 

 iris-diaphragm on the surface of the cylinder was a very useful adjust- 

 ment, by means of which the surface of the illuminated field could be 

 easily limited. In front of the source of light there was a little con- 

 denser, which could be independently focused, and in front of the tube a 

 trough was provided— to contain a solution of sulphate of copper or other 

 liquid, for producing monochromatic light, or a piece of monochromatic 

 glass ; or a piece of glass with a central patch could be introduced for 

 obtaining dark-ground or oblique illumination. The great advantage 

 of being able to modify the intensity of the light without disturbing 

 any of the apparatus connected with the Microscope — which was a special 

 feature of this kind of lamp — was obtained by racking the electric lamp 

 to or from the end of the glass rod ; the lamp could also be used very 

 low down, as it could be placed almost close to the table. The whole of 

 the apparatus was carried upon a block, so arranged that it could be 

 swung in almost any direction, which rendered this an almost universal 

 lamp. Where electric current was not available, an inverted gas-mantle 

 could be effectively substituted, the structure of the mantle being com- 

 pletely broken up by the reflections inside the glass rod ; this was 

 further effected by the end of the rod next to the light being slightly 

 and very finely ground, the outer end being polished. 



