1900] MICROSCOPICAL JOURNAL 99 



scribes at length in the Journal of Geology. It is a dike 

 rock, consisting essentially of analcite, orthoclase, plagio- 

 clase, and cegyrite, the analcite having the character of a 

 base in which the other minerals form radiating groups 

 of crystals. The analcite clearly represents the magma 

 left after the crystallization of the imbedded minerals, and 

 it is evident that it can be formed only from a magma 

 highly charged with water, and therefore under pressure. 

 The labelling of microscopic objects, when done prop- 

 erly, forms a not unimportant part of the training of a mi- 

 croscopist. Apart from the discipline that it affords in 

 habits of painstaking research, the systematic record that 

 a label contains is a great time saver to the student, inas- 

 much as, when it is necessary to refer to the object again 

 or to compare it with a series of objects belonging to the 

 same genus, he is enabled to see at a glance the relation 

 that each object bears to the other in the system of class- 

 sification that is adopted, thus rendering further refer- 

 ences to text and notebooks unnecessary. The labels in- 

 clude Sub-kingdom, Class, Order,Family, Genus, Species, 

 Name, Section, Medium, Special Points, Locality, Mount- 

 er, Date, and should be printed in sheets and details fill- 

 ed in before the lables are trimmed to size. They are 

 placed on the slide, one on either side of the object. 



Resolution. — The question of the limit of resolving 

 power of objectives is discussed by Dr. L. B. Twitchell, 

 who points out that up to the present, Nobert's twentieth 

 band, 225,190 lines to an inch, has never been resolved, 

 and, theoretically, with white light only 146,543 lines per 

 inch can be distinguished. By utilizing, however, the 

 shorter actinic rays and a photographic plate, theoret- 

 ically 193,037 lines per inch should be resolved— that is, 

 effects beyond the possibility of ocular vision. 



Formalin,— Mr. G. E. Stone has used formalin in his 

 laboratory for six years for the display of tke morpho- 



