412 PEOCKEDINGS OF THE SOCIETY. 



the apparatus were explained to the Meeting by reference to a diagram 

 and by the exhibition of the instrument itself. 



The Chairman said he had the pleasure some time ago of examining 

 Mr. Gordon's apparatus, which was undoubtedly a very ingenious device 

 for illuminating objects under the Microscope by means of a light source, 

 which had hitherto been intractable. What especially struck him was 

 the simple and effective way in which the intensity of the light could be 

 regulated as required, without disturbing any focal or aperture adjust- 

 ment. A well defined circular light-source could of course be obtained 

 from any sufficiently extended flame by the simple expedient of placing 

 a piece of perforated sheet metal in front of it, but the intensity of such 

 a source could not unfortunately be easily and satisfactorily regulated. 



Mr. J. E. Barnard said that he gathered from Mr. Gordon's paper 

 that he had discarded the Nernst lamp because of its want of durability. 

 This was an objection when they were first introduced, but they appear 

 to be less subject to this now than formerly. If a Nernst filament runs 

 for the first fifty or sixty hours without fracture, it then appears to enter 

 on a longer life, and will often run for a long period. He had used a 

 1 -ampere Nernst lamp for the last two or three years, and during that 

 period the filament had not been renewed. He used it nearly always 

 for short periods, when it was turned on and off frequently, which was 

 rather a severe test, but it was still working satisfactorily. He thought 

 it was to be recommended as it gave a much greater degree of luminosity 

 per unit area of filament than any carbon or metallic filament electric 

 lamp. As regarded the tubular lamps, they were subject to a very great 

 drop in intensity after having been in use for a time, and he thought if 

 Mr. Gordon could get a carbon lamp in a small tube as suggested, he 

 would find the drop to be very considerable, because the smaller the 

 tube the more rapidly would the lamp deteriorate. He thought it 

 might really be considered that a Nernst lamp would be the best for 

 the purpose. 



Dr. Spitta did not agree that Nernst lamps were at all reliable, and 

 he deprecated any attempt to use them on this account. He was speaking 

 of the smallest size, not the half ampere, which in his experience he 

 found much more durable. It was only fair to state, however, that he 

 understood the Company were bringing out a new pattern, which they 

 hoped would be half the price and quite efficient. 



Mr. Barnard said he should explain that he had taken the precaution 

 never to run a lamp on the full voltage it was made for, but always 

 reduced this 7h p.c. to 10 p.c. If this was allowed the lamp was found 

 to work well. The makers suggest that some allowance should be made 

 in this respect, but it is quite practicable to allow a much greater margin 

 than they suggest, with the result that the life of the filament is greater. 

 The only practical objection to this is that the preliminary heating up 

 period is somewhat increased, but this is a small objection for micro- 

 scopic or similar scientific purposes. 



Mr. Wesche thought that for general Microscope work there was 

 nothing better than a good paraffin lamp. While admitting the ad- 

 vantage of the more powerful illumination of electric lamps, he had 

 experienced much waste of time and trial of patience through the break- 

 ing of filaments and the failure of fuses. 



