Journal of Applied Microscopy. 



499 



The curve which follows is plotted by taking the magnifying powers and the 

 focal depths as coordinates. 



Curve showing relation between focal depth and magnification. 



The curve approximates an equilateral hyperbola, and indicates that the focal 

 depth varies inversely with the magnifying power. 



In order to compare the constancy of the various settings with the magnifying 

 power used, the probable error of the mean was computed for eye-piece A. The 

 results follow : 



A— 1. A— 1-2. A— 1-3. A— 1-4. A— 1-6. No. 3 Leitz. 

 0.57 0.15 0.18 0.05 0.05 0.24 



Leon E. Ryther. 



Physical Laboratory, The University of Maine. 



One Way to Number Collections and to Keep Data. 



The student just beginning his laboratory course can scarcely realize, at the 

 outset, that material and data are destined to accumulate at a rate that must 

 puzzle him before he is graduated, embarrass him as an instructor, and perplex 

 him when advanced to the head of a department. It seems wholly wrong that 

 students, especially graduate students, who are those sifted out of the great 

 student body to become instructors, should not have the benefit of some regular 

 instruction, or hints at least, touching the matter of keeping notes and catalogu- 

 ing objects. Unfortunately, we are seldom led in this matter, as in other affairs, 

 to profit by the experiences of others, but are turned out in our several vocations 

 to evolve out of our inner consciousness methods of our own — a course which 

 may foster originality and personality, without necessarily giving the best results. 



It is a characteristic of all amateurs and beginners — and not infrequently of 

 some others — to allow the accumulations of several years to go unnumbered and 

 unrecorded, awaiting the time when some system of cataloguing may "turn up." 

 Too often this means to the end of a natural lifetime, as those can attest who 

 are curators of museums, and who often receive collections of several thousand 



