186 THE MICROSCOPE. 



for their study and fits one for a happy time over the mosses. 

 We hope some one will prepare a similar book on American 

 mosses. 



Microbes on Postal Cards. — Bacilli have been found 

 alive after 20 houis existence on a postal card. A letter was 

 infected by cholera bacilli, put into the mail; when taken out 

 24 hours later the bacilli were alive. 



Microscopes for Druggist. — The number of Druggists who 

 own and can use a microscope is rapidly increasing owing to 

 the adulteration of drugs and other causes. The instrument is 

 being used in the colleges of pharmacy and state associations 

 begin to have sections of microscopy. 



QUESTIONS ANSWERED. 



Note.— Dr. S. G. Shanks, of Albany, N. P., kindly consents to receive all sorts of ques- 

 tions relating to microscopy, whether asked by professionals or am, it, us Persons of aU 

 f ades of experience , from the begt ner upwat d, are welcome to the bentfits f tins depaf 

 ment. The questions are number, d /or Juture > eference. 



175. What is an aplanatic system eye-piece ? — S. 



An aplanatic eye-piece is usually one of the achromatic forms 

 (such as the Priscopic), in which spherical aberration is, as 

 nearly as possible, eliminated. Any eye-piece presenting a 

 fiat field with no peripheral distortion is aplanatic. 



176. What is the highest power objective yet made t — S. 



The 1-75 inch objective made by the late R. B. Tolles, of Bos- 

 ton, in 1878, and owned by Dr Ephraim Cutter of New York, 

 is probably the highest power objective yet made for actual 

 work. 



177. What is Helinmicroscopy f — S. 



Heliomicroscopy means the use of direct sunlight for illum- 

 inating the object, either for critical resolution or for the pro- 

 jection of the image on a screen. 



178. / have 30 mounted diatoms and wish to classify and name 

 them. What books do I need for the purpose? 



The Am. Mo. Mic. Journal, Vol. xii, (1890), contains a series 

 of papers on the life history and classification of cUatoms. 



