96 THE AMERICAN MONTHLY [Mar 



LETTERS TO THE EDITOR. 



GATES' DOUBLE MICROSCOPE. 



Not New.— This microscope does not differ in principle 

 from that described by Dr. Royston Piggott before the 

 Royal Society in April, 1870. He stated that the general in- 

 terpretation of the Podura scale was incorrect, and heg-ave 

 an illustration of what he had proved it to be by this means, 

 but which no one has been able to see, and which other mi- 

 croscopists have declared (consequently ?) to be spurious, 

 and still later that his theory was wrong. His remarks, 

 however, created a great reduction in residuary aberra- 

 tion in micro-objectives. He exhibited to Messrs. Powell 

 and Lealand an imag-e of Pleurosig-ma ang-ulatum with a 

 power of 4,000 diameters, from an }i'm. object-glass, with 

 clear and distinct beading-. I have used it and found it very 

 interesting-, but very difficult to g-et good results, and never 

 succeeded in g-etting- differentiation which I had not obtain- 

 ed before.— R. O'H. 



Important. — The invention of Professor Gates I look 

 upon as most important, and is on the same lines as some 

 experiments I made about 15 years ag-o. — R. J. Nunn. 



Slides. — -Where can I g-et mineralogical and microscop- 

 ical specimens mounted opaque without glass cover but 

 capped to keep out the dust. Cap to be removed when 

 specimen is put under the microscope. — C. VB. 



EDITORIAL. 



To those public libraries not already subscribers to this 

 journal, (thoug-h most of the larg-e ones are already on our 

 list), who send subscription for 1899 ($1.50), we will make 

 a. present oi THREE BOUND VOLUMES, 1895, 1896, 1897. 



A Delicate Experiment. — Delag-e divided an eg-g- of a 

 sea-urchin under the microscope into two parts, one con- 

 taining the nucleus and the centrosome the other simply 

 cytoplasmic. Beside them he placed an intact ovum and 

 then let in spermatozoa. All three objects were fertilized, 



