430 Address by the President. [Sess. 



shown in Fig. 3, Plate L., in which it will be seen how small 

 a part of the sub -stage condenser is utilised. The letters 

 represent the same things as in Fig. 2. This shows the 

 advantage of having the condensing-lens fixed to the lamp 

 and correctly centred to its flame, as is done in the Beck 

 " complete " lamp and some lamps of other makers. 



A good way to get excellent results is to turn aside the 

 mirror and send the light direct from the lamp into the sub- 

 stage condenser. This, however, can only be done when the 

 microscope is placed sufficiently high on its trunnions to en- 

 able the proper inclination of the body to be made, and the 

 lamp flame can be brought sufficiently low. 



A very pleasant form of illumination for certain objects is 

 what is called dark-ground illumination — that is, the whole 

 field of the microscope is dark except the object, which is 

 brilliantly illuminated. This is effected by placing in the 

 turn-out arm of the sub-condenser a metal disc having parts 

 of the margin cut away at regular intervals but the centre 

 left entire. This entire centre must be larger or smaller 

 according to the aperture of the object-glass used. By this 

 arrangement the central rays from the sub-stage condenser 

 are prevented from entering the microscope, while the object 

 is illumined by the oblique rays only. The arrangement of 

 the light, as shown in Fig. 2, Plate L., is the best for this 

 kind of illumination. 



I have said nothing about illumination by polarised light 

 or illumination for photo-micrography, as these subjects would 

 lead me far beyond my present limits. I cannot, however, 

 close these remarks without acknowledging my indebtedness 

 to Mr E. M. Nelson, who, by common consent, is recognised 

 as one of the first experts in microscopical manipulation in 

 the country, and at whose feet many years ago I sat as a 

 learner. 



I would just add a few words about the care of the micro- 

 scope, which is an expensive instrument. Whatever kind of 

 microscope you buy — large or small — let it be of the first 

 quality, and take care of it, and you will derive satisfaction 

 from its use. Most large microscopes require to be folded in 

 some way to be put into the cases in which they are bought. 

 If they are to be much in use, avoid this folding as much as 



