Vol. 6, 1920 
PHYSICS: 0. BLACKWOOD 
253 
The British West Indies colored race starting with a sex ratio of 103.64 ± 
2.75 in the offspring of primipara shows in subsequent births a ratio of 
112.02 ± 2.76 while in the European pure the ratio of first births is 115.51 
=±=1.5 and subsequent births show a decrease of males; the ratio being 
97.33 ± 1.18. 
So also the differences between "pure" and "hybrid" races are in the 
opposite direction in the colored and white races. The "pure" European 
have a sex ratio of 104.54 ± 0.97 and the European hybrids a ratio of 122.86 
=•= 2.14 — showing an excess of males. On the other hand the British West 
Indies colored which as we have seen is, compared with the United States 
colored, relatively the purer, has a ratio of 107.92 ± 2.65, while the 
United States colored has a ratio of 96.12 ± 1.76 an excess of females. 
It seems, therefore, that the following conclusions as regards material 
in the records of the Sloane Maternity Hospital of New York City, may 
be drawn as a guide for further investigations. 
(1) Hybrid white matings give a significant excess of males over "pure" 
white matings. 
(2) Hybrid colored matings give a significant excess of females over 
relatively "pure" colored matings. 
(3) The difference between the sex ratio of the United States born 
whites and the United States born colored is nine times its probable error. 
(4) In "pure" European matings the offspring of primipara have a sex 
ratio of 115.51 =±= 1.5, while the offspring from subsequent births have a 
ratio of 97.33 1.18. The difference is 9.7 times its probable error. 
(5) In the hybrid matings studied no such difference between the sex 
ratio of offspring of primipara and of subsequent births exists. 
(6) The sex ratios of the United States white births recorded is not 
significantly different from that of hybrid European matings. 
1 Proc. Soc. Exp. Biol. Med., 1919. 
2 Biol. Bull, 1908. 
THE EXISTENCE OF HOMOGENEOUS GROUPS OF LARGE IONS 
By Oswald Blackwood 
Ryerson Laboratory, University of CmcAGO 
Communicated by R. A. Millikan, March 12, 1920 
The Zeleny mobility apparatus has been modified by the author sa 
as to be capable of giving a decisive answer to the question as to whether 
the large ions produced by spraying distilled water are of many different 
sizes or whether — as claimed by certain observers^ — only a few different 
sizes are present in the ionization. In other words, is there a continuous 
spectrum of mobilities or a line spectrum? The investigation is fully de- 
scribed in an article which is about to appear in the Physical Review. 
The mobility apparatus consists of a brass cylinder 160 cm. long and 
