122 



THE AMERICAN MONTHLY 



[July, 



solution added to water containing 

 infusoria, causes the ciliary action to 

 become visible. Too much kills the 

 animals instantly. The author be- 

 lieves that this reagent will prove of 

 great value in microscopical investiga- 

 tions of infusoria. 



Address to the Members of the 

 Royal Microscopical Society.* 



BY PROF. F. MARTIN DUNCAN, F. R. S. 



Every Fellow of this Society who 

 has attended the evening meetings 

 during the last twelve months must 

 have been struck with the very prac- 

 tical nature of our proceedings, and 

 that the observations made, and the 

 apparatus exhibited and described on 

 those occasions, indicated a growing 

 desire for the perfection of the micro- 

 scope. At the same time it must 

 have been evident that the applica- 

 tion of the instrument to its proper 

 purposes is open to many sources of 

 error, and that there is an amount of 

 intelligence and knowledge required 

 in the management of the micro- 

 scope, which is the result of much 

 labor, thought, and experience. Com- 

 mon sense might tell everybody this, 

 but it sometimes happens that when 

 a man has invested a certain number 

 of guineas in an instrument, he imag- 

 ines he is correspondingly endowed 

 with the abilities of a microscopist in 

 the true sense of the term. On the 

 other hand a very large number of 

 able men become possessed of instru- 

 ments humble in appearance and not 

 costly in any sense, and they rest sat- 

 isfied that a microscope is a micro- 

 scope, and believe, therefore, that 

 they see the true invariably. One of 

 the benefits of belonging to our soci- 

 ety is the opportunity of seeing ob- 

 jects properly shown by the ablest 

 manipulators, and of hearing commu- 

 nications on the imperfections and 



* From Microscopical A'cw-; — abstract from 

 the 'Votirrtiil A'. M. Societv. 



corrections of the instrument, and it 

 would be well if our list, full as it is, 

 were crowded by those scientific men 

 who constantly use the microscope in 

 original research in biology. A con- 

 siderable experience impresses me 

 that the majority of students, and not 

 a few professors, not only use indif- 

 ferent instruments, but also carefully 

 avoid all those practices which we 

 know are absolutely necessary for 

 correct microscopy. A thing is seen, 

 therefore it must be real ; one man 

 sees a spiral line, another a circle, 

 another a series of dots, using the 

 same object and different micro- 

 scopes. They describe and debate, 

 and each is self-satisfied. Yet all the 

 while had they had a master in mi- 

 croscopy their differences could be 

 terminated. 



A pleasant evening with the micro- 

 scope generally means a painful time 

 for the eye. A good glare of light, 

 thanks to lamp, condenser, mirror, 

 and forgotten diaphragm, appears to 

 be almost invariably a desideratum to 

 the beginner. Experience teaches, 

 however, and the advanced micro- 

 scopist never uses more light than is 

 absolutely necessary, and increases 

 and diminishes the illumination dur- 

 ing the careful observation of an ob- 

 ject, not only by employing a less 

 intense source of light, but also by 

 using diaphragms of different sizes. 



Since microscopy has been ex- 

 tended to the examination of sections 

 of rocks composed of different min- 

 erals, the truth that some can be 

 roughly distinguished by their dichro- 

 ism under the polarizing ray, the ana- 

 lyzer not being used, has become ap- 

 parent. The polarizer is also useful 

 in another manner. Researches have 

 been undertaken to examine into the 

 influence of the polarizing ray upon 

 substances which may or may not 

 give the usual phenomena under the 

 analyzer. Polarized light carefully 

 manipulated, is very useful in exam- 

 ining thin sections of corals, which 

 are made up of closely placed fusi- 

 form and long alternating prisms, 



