The President's Address. By Prof. P. Martin Duncan. 183 



It is a matter of great congratulation that the Society 

 maintains its character at home and abroad as a useful and truly 

 scientific institution. There is no doubt that great progress has 

 been made in microscopical science during the last few years and 

 that the communications read before this Society, the recorded 

 debates and their influence on our large and increasingly important 

 number of Fellows have assisted in this satisfactory state of things. 

 The Society may take the credit of having now completely 

 eradicated the old and very erroneous notions regarding what was 

 called " angular aperture," and of having disseminated and estab- 

 lished the knowledge of aperture in its correct signification and the 

 use of the "numerical aperture" notation. The first term has, 

 indeed, almost ceased to be employed by advanced microscopists. 

 The homogeneous-immersion principle has been developed and the 

 media which have been proved to be so valuable have originated 

 with Fellows of the Society and have been recorded in the 

 Journal. 



I feel a sensation of some pride that I should be able to hand 

 over the presidency of this Society in the midst of its useful and 

 prosperous career to an observer of the highest class of excellence, 

 whose success has been assured by the employment of the instru- 

 ment which has been largely perfected by the intellectual and 

 mechanical gifts of Fellows of this Society. I may, I trust, 

 (without the least desire to stop the particular physical and mathe- 

 matical tendencies of many of our Fellows) urge the great number 

 of good observers of nature amongst us to be stimulated by the 

 very valuable reports of the researches on the structures of the 

 invertebrata and plantse, which appear in the Journal — a com- 

 pendium of which the Society may justly be proud — to undertake 

 work which may come before their future President and receive 

 his criticism. In fact it may be hoped that that excellent Journal 

 will contain more records of the labours of the Fellows of the 

 Society. 



In the proceedings of all great Societies there are occasions 

 when congratulations and the desire for future usefulness have to 

 give place to very opposite expressions. Men toil and pass away, 

 and others enter into their labours. 



The present occasion is no exception to the rule. We have to 

 deplore the loss of three great practical opticians, two of them being 

 microscopists of the highest renown. One had attained an age far 

 beyond that which is usually noticed amongst men who have 

 laboured with head and hand, and on looking back at his life it 

 must be admitted that by his means an immense amount of 

 intellectual pleasure was given to the world, and a great amount of 

 exact knowledge has been consolidated. 



For fifty years the name of Powell has been a household word 



