ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



705 



In another report* of the measurements the matter is thus dealt 

 with. 



" While of course these measurements have no tendency to prove 

 the possibility of identifying blood by the diameter of the corpuscles, 

 they are admissible to show that under exactly the same conditions 

 there is an average diameter of the blood-corpuscles of an individual 

 which varies within exceedingly narrow limits, and that this diameter 

 may be measured with very great accuracy. The limits of error 

 certainly fall within the 1/200,000 in., and probably within the 

 1/250,000. Whether this average diameter varies from time to time 

 is a question not yet determined." 



Boecker's Holder for Analysing Prism and Goniometer. — This 

 (fig. 145) serves not only to hold the analysing prism, but can also 

 be used for a Leeson's goniometer. 



Fig. 145. 



Fig. 146. 



The apparatus is attached to the body-tube by the ring a b, over 

 which is fixed the divided circle c d. Within the latter turns con- 

 centrically the tube e /, with a bevelled plate on which is the index- 

 mark. This tube receives either an analysing prism or the doubly- 

 refracting achromatic quartz prism of Leeson's goniometer (fig. 116). 

 The rotation of the tube can be prevented when desired by the clamp 

 screw r. 



"An Improvement in Objectives."t — This is another paper by 

 Mr. E. Gundlach, which we reproduce in its original form : — 



" Eight years ago I presented to the American Association for 

 the Advancement of Science a description of a new quadruple 

 objective for astronomical telescopes.^ The general acknowledgment 

 with which the paper was received, and the high estimation of the 

 theoretical princijiles of the invention by scientific authorities of this 

 country as well as Europe, encourage me to present to this Society 

 a description of another improvement in objectives, which I expect 

 will be of equal value for both the telescope and the Microscope. 

 Although I have uufortiuiately not had sufficient opportunity for 

 properly executing an objective of the above-mentioned description, 

 and thus practically demonstrating its advantages, I must confess 

 that during the time I have become conscious of a practical defect, 



♦ The Microscope, v. (1885) pp. 113-4, from 'Legal News.' 



t Proc. 7tli Ann. Meeting Amer. Soc. Microscopists, 1881, pp. 148-52. 



X See this Journal, ii. (1879) p. 75. 



