HANDBOOK OF MOSSES. 



done for science has been done with comparatively in- 

 expensive instruments. 



The most useful cheap instrument I know, is Field's 

 School Microscope, a very compact little instrument, having 

 three simple lenses, which, separate or combined, give a 

 magnifying power of from five to forty diameters. This, 

 with the simple lenses, live box, needle, and other appli- 

 ances, costs los. 6d, ; a compound body may be added for 

 2s. 6d. extra. This will give powers of from twenty to 

 eighty diameters. It is well to have this compound body at 

 first, as the cabinet is then made of sufficient size to hold 

 the compound body and all the other apparatus. For an 

 additional 2s. 6d. a Wollaston doublet may be added ; and, 

 as this lens is a combination of plano-convex lenses placed 

 in such a manner and of such a focus as to reduce 

 chromatic and spherical aberrations, for i$s. 6d., it is 

 possible to possess a microscope nearly achromatic, giving 

 a power of 120 diameters, which is sufficient for almost all 

 the work which the young botanist will have to do. All my 

 own earliest work in mosses was done with this instrument, 

 and I believe I learned more by its aid than I have ever 

 done with the more expensive instruments I have since used. 

 As a simple microscope it will always be useful for dis- 

 secting and mounting purposes, and I can say with con- 

 fidence, that the student who has acquired all the knowledge 

 of structure that this cheap little instrument will place with- 

 in his reach will have gained such an insight into the moss 

 world as will enable him to determine with a little patience 

 the most difficult of mosses. 



