234 ADJOURNED DISCUSSION IN LONDON 



IJ inch, of one of the solid glass rods supplied by Messrs, Beck, for 

 half an hour at a time, without the slight-est damage to the glass, 

 and I am inclined to think that this " bogey " of the danger to 

 your collecting lens is somewhat over-rated. 



Mr. C. Beck: Has Commander Ainslie tested the amount cf 

 light lost by absorption from glass to glass. Is it 75 per cent. ? 



Commander Ainslie : Yes, of course, a great deal of light is 

 lost. It was a question of the capability of the glass to withstand 

 heat. It is a question of the size of the illuminant. I have seen 

 a piece of ground glass as the source of illumination instead of the 

 crater of the arc itself. 



Mr. Maurice Blood : You can use a large collecting lens. 



Commander Ainslie : But you will not get more light, because 

 it is the intrinsic brilliancy of the light that counts. 



Dr. R. Clay: The feature that pleases me most in the micro- 

 scopes that Mr. Beck has show^n is the provision that he has made 

 by which one can start with a simple form and gradually build it 

 up. I have been advocating this for some time, and I am very glad 

 to see it is accomplished here. That a student who has not too much 

 money can commence with an inexpensive instrument and add to it 

 as he goes along, and as he feels the necessity for and understands 

 the use of improved apparatus, is a very great advantage. 



I was very much interested in Commander Ainslie's formula 

 connecting the area illuminated by a substage condenser and the 

 aperture of the condenser. I think it is one of the most important 

 things that has been brought forward during this Symposium, because 

 there is quite a lot of nonsense talked about the illumination of 

 microscope objects, and that formula puts the whole in a nutshell. 

 I was also interested in the paper on the illumination of metallurgical 

 specimens, as I think it is possible with a prism that I devised some 

 time ago for another purpose to. give the 50 per cent, illumination 

 that has been asked for in that paper. 



Mr. W. R. Traviss: I should like to mention that it is over 35 

 years ago since I introduced to Messrs. Swift and Son a microscope 

 on the lines of the one that the last speaker has said he would like 

 to see, viz., an instrument that could be commenced in a small way 

 and gradually built up as time goes on. 



The simplest form had a firm tripod, of which the toes of the 

 legs were cork-filled to give firmness. The stage was a cut-open form 

 recommended by the late Dr. Dallinger and Mr. E. M. Nelson. 

 The coarse adjustment was made by the body sliding in a cloth lined 

 fitting. The screwed holes for the attachment of the limb or arm 

 to the stage were made a standard distance from the optical centre, 

 so that a coarse adjustment with rack and pinion movement could 

 be exchanged. The side edges of the stage were grooved for the 

 vertical movement of a mechanical stage or roller sliding bar which 



