344 MR. K. PEARSON ON THE MATHEMATICAL THEORY OF EVOLUTION. 
Part II.—PRractican. 
Statistical Examples. 
Page. 
Section 21.—The range of the barometer. . . ay iag Sst al SS) “US ee ye De 381 
Section 22.—Crab-measurements (Weldon No. 4), an OEE te Lcd Vee AN A W'S” A 384 
Sechions23:—Viariationyineherghbotmcecruits yee ca nineteen enn rnin n-ne ne nO 385 
Section 24.—Variation in height of school-girls aged 8. . . E. 4a(h Sey Some aE ane 386 
Section 25.—Variation in length-breadth index of 900 Bavarian Aieills fl a ee ee 388 
Section 26.—Frequency of enteric fever with age. . . .....2.2.+.+:5. +... 390 
Section 27.—Distribution of guesses at mid-tints . . ...... +... .2. =~. . 392 
Section 28.—Distinction between “skewness” and ‘“‘compoundness” in case of crabs’ 
SUTOrcheadsiacp yes nes Kieec ars mrieh he Re rma ey ee MN eee Nera Cin ak GN sal ech" 6. + 394 
Section 29. Civequency of divorce with aaeation OMENGEEY 955g Noho 1g 0 DO 395 
Section 30.—Frequency of houses with given valuations . . . . ........ +5 396 
Section 31.—Variation in number of petals of butterceups. . . . 2. 1. - 1 ee ee 399 
Section 32.—Variation in number of projecting blossoms in clover. . . . ..... .- 402 
Section 33.—Variation in number of dorsal teeth on rostrum of prawn . ...... . 403 
Section 34.—Variation in pauper-percentages in England and Wales. . . . .... . 404 
Section 35.—Resolution of mortality curve for English males into components. . . .. . 406 
Section 36.—Concluding remarks on skewness, variation, and correlation (correlation ovals 
forswhist) eee ene ee re ARR rE Meet m saul! GS Pano. 6 410 
Note on THIELE’s treatment of Meare praqtenes See Oe eee Pee en? calla Mra. ™c 412 
‘Part 1.—THEORETICAL. 
Asymmetrical Frequency Curves. 
(1.) AN asymmetrical frequency curve may arise from two quite distinct classes of 
causes. In the first place the material measured may be heterogeneous and may 
consist of a mixture of two ar more homogeneous materials. Such frequency curves, 
for example, arise when we have a mixed population of two different races, a homo- 
geneous population with a sprinkling of diseased or deformed members, a curve for 
the frequency of matrimony covering more than one class of the population, or in 
economics a frequency of interest curve for securities of different types of stability— 
railways and government stocks mixed with mining and financial companies. The 
treatment of this class of frequency curves requires us to break up the origina! curve 
into component parts, or simple frequency curves. This branch of the subject (for 
the special case of the compound being the sum of two normal curves) has been 
treated in a paper presented to the Royal Society by the author, on October 18, 1893. 
The second class of frequency curves arises in the case of homogeneous material 
when the tendency to deviation on one side of the mean is unequal to the tendency 
to deviation on the other side. Such curves arise in many physical, economic and 
biological investigations, for example, in frequency curves for the height of the 
barometer, in those for prices and for rates of interest of securities of the same 
class, in mortality curves, especially the percentage of deaths to cases in all kinds of 
