53S PROCEEDINGS OF THE SOCIETY. 



a delicately poised balance, was indicated by a diagram drawn on the 

 board, lie at first tried a copper box to contain the air, but this did 

 not answer owing to the critical expansion of the copper about the 

 temperature of 100° F. which brought about a gradually rising tempera- 

 ture in the stage. He then successfully tried the effect of placing 

 within the brass box forming the stage a number of glass bulbs as shown 

 by a further diagram. Heat from the flame was conducted by means 

 of a silver rod which dipped into a paraffin bath attached to the side of 

 the stage itself. The entire arrangement was found to answer admirably, 

 and an almost constant temperature could be maintained for a very 

 considerable time. 



Mr. Cecil R. C. Lyster also exhibited an improved form of electrical 

 warm stage. He said that most of those previously made on this prin- 

 ciple were heated by means of resistance coils, but he found that it was 

 impossible to maintain an equable temperature in this way from the 

 ordinary house current on account of its constant variations of intensity, 

 for though it was nominally 100 volts it was not constant, sometimes 

 rising to 103 and at others falling to 07, which caused considerable 

 alterations in the temperature of the resistance coil. He had therefore 

 endeavoured to find something which would obviate this inconvenience, 

 and had found that by using Cryptol (A. Gallenkamp & Co.) as a 

 resistance, a perfectly even temperature could be maintained as long as 

 the current was passing. The amount of current consumed was ex- 

 tremely small, not exceeding 150 milliamperes, a quantity which was 

 insufficient to work an electric meter, so that practically the arrange- 

 ment could be worked for nothing. He regretted that he was unable to 

 show the apparatus in action that evening, for although he had brought 

 it to the meeting, he found that the current supplied to that building 

 was 200 volts, whereas the resistance of the stage exhibited was only for 

 100. 



On the motion of the Chairman a hearty vote of thanks was passed to 

 Dr. Barlow and to Mr. Lyster for exhibiting and explaining these very 

 ingenious and simple contrivances to the Society. 



Mr. C. L. Curties exhibited an improved dark ground illuminator 

 for high powers. He said he had received some time since an adapter 

 from Messrs. Leitz, of Wetzlar, having a central dark stop for use near 

 the back lens of one of their x \ 2 inch oil immersion objectives, and when 

 this was employed with a special low-angle condenser, having rotating 

 diaphragms and centring screws, making it suitable for Leitz' Micro- 

 scopes, very good results were obtained. As, however, this adapter 

 could only be used with objectives of Messrs. Leitz' manufacture, he 

 had made an adapter with interchangeable stops fixed to pins, w 7 hich 

 were carried in the centre of the adapter, thus making it suitable for use 

 with objectives of any make. He had found that when using an 

 achromatic condenser of the ordinary type, stopped down a certain 

 amount, all the results obtained by means of the special condenser 

 were reproduced. He was showing Pleurosigma angulatum with this 

 arrangement on a dark ground under a ^ inch oil immersion objective 



