ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
787 
total image resulting in this way is divided into fields of different 
intensity. 
The greatest diameter of the imago proper D E F amounts to about 
17, the greatest width of the pale-yellow border to 8 /x. A further 
concentration of the light is only possible by diminution of the effective 
aperture or of the object-distance. 
Introduction of a Universal Scale of Magnification of Micro- 
scopical Figures.* — M. P. F. Reinsch complains that every micro- 
grapher makes use of an arbitrary scale for his figures. The camera 
obscura gives, for the same combination of objective and eye-piece, a 
constant magnification of the object figured ; but the Microscopes of 
different makers differ widely, and the magnifications of the systems 
of objectives and eye-pieces do not vary in the same proportion. Conse- 
quently the statement as to the eye-piece and objective employed, made 
by authors on their figures, conveys little meaning to those who have 
not the same Microscope at their disposal. 
In the systematic description of microscopical plants, it is of the 
utmost importance to give the dimensions in absolute value. For 
microscopical work such as this, the micron /x has been chosen as the 
unit of measure. A scale of magnification should be also based on the 
same unit. Measurements are indispensable in order to compare 
specimens of algae and microscopic fungi with the published figures, but 
the work is complicated by the variety of magnifications used by authors, 
and long calculations are often necessary in order to find the absolute 
numerical values required. 
To draw figures in conformity with the base of the measurements, 
the Microscope must be brought to the desired magnification. 
Taking fx as unit, the following magnifications are recommended : — 
Magnifications 
in | u. 
Coefficients. 
2500 (dimens, of the figure) divided by 2 • 5 = n /x (absolute value). 
2000 
» 
2 
= n /x 
1500 
1*5 
= n fx 
1000 
multiplied by 1 
= n fx 
500 
»> 
2 
= n fx 
250 
» 
4 
— n [x 
200 
»» 
5 
= n fx 
125 
8 
= n /x 
100 
55 
10 
= n /x 
Only those coefficients are practicable which, multiplying or dividing 
1000, give whole numbers as product or quotient. Magnifications 
greater than 1000 are obtained by multiplying, those less than 1000 by 
dividing 1000 by the coefficient. The above scale, which represents the 
magnifications which it is in this way possible to express in whole 
numbers, will answer all the requirements of microscopical figures. 
* Bull. Soc. Bot. France, xxxvi. (1889) p. ccvii. 
