140 PREPARATION AND MOUNTING OP MICROSCOPIC OBJECTS. 



nating the negative, having a good bull's-eye lens as a condenser, 

 so arranged with its flat side next the lamp that the refracted rays 

 shall just fill the whole of a double convex lens of about six inches 

 in diameter, the latter being placed in such a position as to refract 

 the rays of light in a parallel direction upon the negative. By 

 this arrangement the bulVs-eye lens of about two inches and a half- 

 in diameter appears as the source of the light instead of the small 

 flame of the lamp. 



" By using a bat's- wing gas-burner of a good size, a single lens, 

 instead of the two, may be so placed as to give the necessary 

 uniformity of illumination." 



This arrangement requires the same care in working as that 

 before mentioned, the picture being produced, developed, and fixed 

 by the same treatment. 



As before stated, almost every manipulator makes some small 

 changes in the method of producing these minute pictures ; but 

 the rules given, though far from new, are sufficient for all purposes ; 

 and I may state with truth, that those which I procured when 

 these wonders were quite new, are fully equal in every respect to 

 the best usually met with at the present time. 



With these instructions I shall close my Handbook, as I believe 

 that every branch of Preparation and Mounting of Microscopic 

 Objects has been treated of. Not that the beginner can expect 

 that he has nothing to do except read this to be able to mount 

 everything ; but there are difficulties from which he may be freed 

 by instruction, when otherwise he would have been compelled to 

 learn by failure alone. I may, here, however, repeat certain ad- 

 vice before given, that, when practicable, it is a good thing to 

 mount each object by two or more different methods, as very fre- 

 quently one feature is best shown dry, another in liquid, and a 

 third in balsam. Secondly, let the mounting be studied thorough- 

 ly, as no part of the microscopic science is more worthy of thought 

 than this. And lastly, let no failures prevent you following up 

 what will assuredly one day become a source of great pleasure, 

 and render your daily " constitutional walk," which is often dull 

 in the extreme, very delightful, as it will afford you some new 

 wonder in every hedge-row. 



