PKOCEEDINGS OF THE SOCIETY. 795 



were presentation slides to him by different donors at various times, and 

 which he had had the courtesy not to refuse. Anyhow, he felt sure 

 the Fellows present would like to thank the donors for their kindly 

 thought in sending the slides to the Society, and he dared say they 

 would be found of some service. 



Mr. C. Beck said that the lamp presented to the Society by Mr. 

 •Gordon was that which he had described at the Meeting in May. The 

 principle of this illuminator was that the light was not taken direct, but 

 by means of cylindrical glass rods, and in this instance three Micro- 

 scopes could be illuminated by the same lamp. The light conveyed in 

 this way overcame the difficulty met with through the image of the 

 filament of an electric lamp appearing in the field when high powers 

 and a focused condenser were used. It also had another advantage in 

 the ease with which the intensity of the light could be regulated by 

 moving the glass rod in or out of the brass tube so as to alter its 

 ■distance from the lamp without disturbing any other arrangement.' 

 When a colour screen was introduced, it greatly reduced the light from 

 •an ordinary lamp, and it was a very difficult thing to increase the 

 intensity of the light to a corresponding extent, but with this device it 

 could be done without any trouble whatever. One end of the rod was 

 ground and the other was clear, and a perfectly homogeneous area of 

 light surface was obtained. (The lamp in question was placed upon the 

 table for examination by the Fellows present.) 



The Chairman said that an illuminant on this system used to be 

 sold by Carl Zeiss about thirty years ago. It was said to give a good 

 diffused light, but some seemed to think it was not altogether satis- 

 factory for critical illumination. 



Mr. C. L. Curties said that a lamp of this kind with bent glass rods 

 was exhibited at one of the Society's Meetings by his father about 

 twenty-five years ago ; he believed it was made by a Berlin firm. 



Mr. A. E. Conrady said that a lamp of this kind was made at Bonn 

 by Koch, whose difficulty at the time was to get glass clear enough for 

 the purpose. 



Mr. Wesche inquired if this lamp could be used with the ordinary 

 electric current supplied to a house. 



The Chairman said the arrangement in front of him was provided 

 internally with a 100-volt incandescent lamp. Mr. Gordon had very 

 kindly presented the Society with two of these, which were intended to 

 be used in series, as the electricians called it, which meant that the 

 current from the main should pass first through one lamp and then 

 through the other. The 200-volt system of the building was by this 

 means suitably divided between the illuminants. If, however, it was 

 desired at any time to employ one illuminant only, it would be necessary 

 to change the internal 100-volt lamp for one that was constructed to 

 carry 200, as in this case there was no dividing the main current with 

 the twin illuminant. It was quite an easy thing to change the internal 

 lamps, but they must be had in readiness, for if it were attempted to use 

 the 100-volt internal lamp when the illuminant was employed by itself 

 the filament would be immediately destroyed. He hoped he had made 

 his meaning clear to Mr. Wesche. 



