ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 725 



given. Example: Required, the number of lines in the ,/,„ of an 

 inch that can be resolved by an objective of 0*65 N.A., with white light. 



"Take the half of 0*3 and the half of the corresponding number of 

 lines, and we find that an objective of 0*15 will resolve 1 L8 lines ; this 

 added to those opposite to 0*5 gives the answer — 490 lines in the 

 T ^q of an inch that can be resolved by an objective of 0*65 N.A. with 

 white light. 



"This method of inspection is much quicker than that of multiplying 

 a constant out by the N.A., but this rule does not apply to the columns 

 "Illuminating and Penetrating Powers" : those figures must be worked 

 out independently. 



"If the values given in the table at the end of the Journal be 

 multiplied by <>-K;S; J > they will be reduced to Sir A. E. Wright's limit, 

 and if they are multiplied by 0*769 they will be reduced to those given 

 in my table on p. 529 (1906). To reduce my table to Sir A. E. 

 Wright's, multiply by 1*083. 



Application of the Method of Rotary Disks to Microscopical 

 Technique.* — H. Lebrun has given much attention to the best means 

 for attaining rapid and systematic examination of microscopic objects. 

 With this purpose in view he has constructed several contrivances. 



1. The Microstereoscope. — This is intended for the examination by 

 museum visitors of small creatures visible, but whose characters are only 

 revealed by a microscopic view. The author arranges a kind of endless 

 chain, on the principle of what are called American stereoscopes, working 

 obliquely upwards. Each link of the chain carries a slide provided with 

 an object, and this object at a certain part of the chain motion falls into 

 a position suitable for observation by a fixed Microscope. Fifty slides 

 are mounted in this way, and can be varied by the museum curator as he 

 thinks fit. The whole arrangement is inclosed in a wooden case pro- 

 vided with a suitable w'indow for admission of light. The body of the 

 Microscope and certain adjustment screws are the only parts visible 

 outside the case. The author uses a binocular, and the magnification 

 employed does not exceed 70 diameters. 



2. A Microscope Table. — This arrangement is suitable for the use of 

 objects requiring high powers. A specially designed table carries the 

 Microscope, and a disk bearing the slides rotates in a constant plane so 

 as to bring the objects successively under the instrument. The table is 

 mounted on four feet, of which the two rear ones are higher than the 

 front, so as to slope the Microscope at an angle of 45° to the horizon. 

 The four feet carry a metallic rectangular frame containing a kind of 

 mechanical stage, to which the Microscope limb is attached without the 

 usual foot. Verniers are attached to the two plates of this stage for the 

 precise measurement of abscissa and ordinates. The rotary disks are 

 secured to a small vertical pin in such a way as to insure constancy of 

 plane, smoothness of rotation, and facility of replacement. The disks 

 may be of metal, wood, or cardboard, and may be solid or perforated. 

 When a disk has been once equipped with a series of slides it may be 

 removed and kept intact for future demonstrations. 



3. Microtome. — In ordinary serial section-cutting it is not unusual to 



* Zeitschr. wiss. Mikrosk., xxiii. (1906) pp. 145-73 (36 figs.) ; also published as 

 an extract. 



