104 THEORY OF STATISTICS. 
during the years 1876-85. A sky completely, or almost com- 
pletely, overcast at the time of observation is the most common, 
a practically clear sky comes next, and intermediates are more 
rare. 
This form of distribution appears to be sometimes exhibited by 
the percentages of offspring possessing a certain attribute when one 
at least of the parents also possesses the attribute. The remarks 
2000 | 
! 1500 
14000] 
~ 
S 500 
; Te 
Dlr. a te A Ee. wr 
Cloudiness 
Fig. 19.—Frequency-distribution of Degrees of Cloudiness at Breslau 
1876-85: 8653 observations. (Table XV.) 
of Sir Francis Galton in Natural [nheritance suggest such a 
form for the distribution of ¢consumptivity” amongst the off- 
spring of consumptives, but the figures are not in a decisive shape. 
Table XVI. gives the distribution for an analogous case, viz. the 
TABLE XVI.—Showing the Percentages of Deaf-mutes among Children of 
Parents one of whom at least was a Deaf-mute, for Marriages producing 
Five Children or more. (Compiled from material in Marriages of the Deaf 
tn America, ed. BE. A, Fay, Volta Bureau, Washington, 1898.) 
Rl Nuiiber of 1! Peni Number of 
Deaf-mutes. Families. 1.0 mutes. Fezailies. 
0-20 220 60-80 55 
20-40 20°5 80-100 15 
40-60 12 — 
Total "3 
92%