214 LECTURES TO SCIENCE TEACHEES. 



high powers ; it acts as it were like an erecting glass, and when 

 inclined at a convenient angle the stage is horizontal, which 

 is very convenient in examining objects in liquid. It is 

 thus a binocular erecting microscope, as Mr. Stephenson calls 

 it. A great many other forms have been proposed, which 

 can be seen in the Exhibition, some having one advantage, 

 and some another, whilst perhaps we may say that some have 

 none at all. 



In conclusion, I may mention the application of spectrum 

 analysis with the microscope. If you want to ascertain more 

 exactly the nature of the light transmitted by any coloured 

 object, you can do so by this means. In the eye-piece arrange- 

 ments there are many things which are required only for special 

 purposes, and but for that the instrument might be made much 

 more simple. It is constructed for carrying on all kinds of 

 inquiries in this subject, and for measuring and comparing 

 spectra together side by side. You can take out the ordinary 

 eye-piece and put in the spectrum eye-piece ; or with a bino- 

 cular microscope you may see the object in its natural form 

 with one tube, and see the spectrum with the other. I have 

 for some years chiefly used my binocular arrangement, which 

 for working is undoubtedly the most convenient, but some 

 parts of its construction are rather unusual and the makers do 

 not particularly like making it, because they do not exactly 

 understand some of the necessary details. 



As I said at first, the entire subject of the microscope is so 

 great that it is quite impossible in the course of an hour to do 

 more than give a hasty glance at some of the leading features. 

 In this Exhibition we have the means of studying all that we 

 can desire. We have the simplest and the most complex, the 

 earliest and the most recent of microscopes ; and I may say I 

 feel tempted to spend many hours in going into the details, in 

 order to thoroughly understand the merits and demerits of these 

 magnificent instruments. I hope that what I have said may 

 enable you to better understand their construction and be of 

 some practical use. I am quite sure that, in the present state 

 of our subject, what we want is to know something of the 

 general principles of the construction of instruments ; but still 

 more to understand the very great importance of proper illumi- 

 nation and of using object-glasses of a proper kind. I must 

 also say, that it is most important to regulate the power which 

 you use for particular purposes. It is mere child's rlav to trv 



