Januaet 17, 1913] 



SCIENCE 



male, and Strong found three sucli dark 

 females. 



If in the female the sex-differentiating fac- 

 tor and the factor for plumage color are 

 placed close enough together in the same chro- 

 mosome to be linked, but not so close that the 

 linkage is complete, " crossing-over " would 

 cause the two factors which entered in the 

 same member of the homologous pair of chro- 

 mosomes to lie in different members and 

 hence to segregate to different gametes. 



K the sex-differentiating factor be M, then 

 the formula for the male is MM and for the 

 female Mm. Let the gene carried by the 

 recessive white pigeon be w and the dominant 

 form of that gene carried by the dark bird be 

 W. The dark female would ordinarily form 

 gametes of the types MW and mw, but would 

 occasionally form gametes Mw and mTF by 

 crossing-over. 



The gametes and their possible combina- 

 tions would be as follows : 



Pj 



White <^ Mw—Mw 



Dark J Mw — MW — mw — inW 



-white c? (exceptional) 



Fi 



Miu 



— white ? 



inw 



_, — dark 2 (exceptional) 

 mW + \ 1 y 



A measure of the linkage between the sex- 

 differentiating factor and the factor for 

 plumage color would be the ratio of crossovers 

 to the total number of individuals which 

 might show crossing-over, viz., 4:59 or Y per 

 cent. 



It should be pointed out that " partial-sex- 

 linkage " signifies the linkage between the sex- 

 differentiating factor and any other factor in 

 the sex chromosome. In the case of Dro- 

 sophila " sex-linked " means only that the fac- 

 tor is carried by the sex chromosome, and as 

 yet no evidence has been obtained bearing on 

 the degree of linkage of the sex-differentiating 

 factor and any of the other factors thus far 

 found in the same chromosome. 



An explanation similar to the one here 

 adopted for the pigeon may be given to Bate- 

 son and Punnett's* results with the silky fowl 

 where partial-sex-linkage in the pigmentation 

 is found. Three other cases of the same sort 

 have been reviewed by Sturtevant," viz., pink 

 versus black eye in canaries, Aglia tau and its 

 variety lugens, and Pygwra anachoreta and P. 

 curtula. 



Two cases of partial-sex-linkage in which 

 the male is heterozygous for sex are reported. 

 At least Sturtevant" so interprets the case of 

 the dwarf guinea-pigs of Miss Sollas, and quite 

 recently Doncaster' finds in cats that certain 

 exceptions in the inheritance of coat-color 

 may be due to partial-sex-linkage. 



Calvin B. Bridges 



Columbia University 



EXPERIMENTS SHOWING THAT COMPLETE RELA- 

 TIVITY DOES NOT EXIST IN ELECTROMAGNETIC 

 INDUCTION 



In the Physical Review for November, 1912, 

 I described in detail some experiments which, 

 taken together with earlier experiments by 

 Faraday and others, establish the fact that 

 complete relativity does not exist in electro- 

 magnetic induction. As a number of en- 

 quiries with reference to these experiments 

 have been made, and as the subject of rela- 

 tivity is one in which great interest is taken 

 by others as well as physicists, it seems de- 

 sirable to give a brief account of the experi- 

 ments in Science. 



Two series of experiments were made, one 

 without iron and the other with iron. In 

 the first series a cylindrical condenser was 

 mounted symmetrically in the approximately 

 uniform magnetic field within a cylindrical 

 electric coil coaxial with the condenser's 

 armatures. The condenser, maintained at 

 rest, was short-circuited, and the coil, tra- 



■* W. Bateson and E. C. Punnett, Jour. Genetics, 

 August, 1912. 



° A. H. Sturtevant, Jour, of Exp. Zool., May, 

 1912. 



"A. H. Sturtevant, Am. Nat., September, 1912. 



' L. Doncaster, Science, August 2, 1912. 



