516 



SCIENCE 



[N. S. Vol. LIV. No. 1404. 



. UNIVERSITY AND EDUCATIONAL 

 NEWS 



The General Education Board and the Car- 

 negie Corporation have jointly promised $100,- 

 000 to the Medical College of the University 

 of Georgia, to be paid at the rate of $20,000 a 

 year for the next five years on condition that 

 a like amount each year is raised from other 

 sources. 



Professor C. J. Tilden, who has been di- 

 rector of the highway and highway transport 

 education committee, in Washington, D. C, 

 since December, 1920, has returned to Yale 

 University to resume his work as professor of 

 engineering mechanics. 



Dr. Frederick H. Falls, of Chicago, has 

 been appointed head of the department of 

 gynecology and obstetrics of the State Univer- 

 sity of the Iowa College of Medicine. 



Dr. T. L. Patterson, formerly of the physio- 

 logic department of the State University of 

 Iowa, has been appointed professor and director 

 of the department of physiology at the Detroit 

 College of Medicine and Surgery. 



D. Walter Munn has resigned his position 

 of professor of engineering and head of the 

 engineering department at the Eoyal Military 

 College to become professor of mechanical en- 

 gineering at the Nova Scotia Technical Col- 

 lege, Halifax, N. S. 



DISCUSSION AND CORRESPONDENCE 

 POSITIVE RAY ANALYSIS OF ZINC 



With the apparatus previously used in the 

 analysis of lithium and magnesium,^ which 

 will be described fully in the Physical Review 

 for December, I find that the element zinc is 

 a mixture of four isotopes, separated by two 

 units in atomic weight. Although slight varia- 

 tions were observed in the relative intensities 

 of the components, they are approximately 

 given by the ratios 6 : 7 : 10 : 1, the heaviest be- 

 ing much weaker than the three lightest. The 

 measurements in themselves do not give the 

 values of the atomic weights with an accuracy 



1 Science, December 10, 1920; April 15, 1921. 



of one unit, but since the separation in each 

 case is exactly two units, and all other elements 

 hitherto analyzed have integral atomic weights, 

 with oxygen ^ 16 as a basis ; we may assume 

 that the zinc components are also integral. In 

 this case the only values possible are the atomic 

 weights 63, 65, 67, and 69, since these values 

 with the above intensity ratios give a mean 

 atomic weight of 65.5 and a displacement of 

 the group one unit either way would make the 

 mean differ by a whole integer from the accu- 

 rately determined chemical atomic weight 65.4. 



A. J. Dempster 

 Etekson Physical Laboratory, 



University of Chicago 



the rediscovery and validity of arca 

 lithodomus sowerby 



Nearly a century ago, in 1827-1830, Mr. 

 H. Cuming made an extensive voyage along 

 the western coast of South America collect- 

 ing natural history specimens. The shells 

 obtained by Cuming were described by Bro- 

 derip and Sowerby. Among the Noah's Ark 

 shells was a most curious species, named by 

 Sowerby Byssoarca lithodoinus^ and figured 

 by Reeve.- The shell was cuneiform, very 

 finely ribbed, and covered with beautifully 

 imbricated scales. It measured 3.5 inches in 

 length and 1 in. height. It was found by 

 Cuming at Monte Cristi, Ecuador, about Lat. 

 1° South. 



In 1840, Gray established for this singular 

 Area the section Litharca, which, in 1887, 

 Fisher recognized as a section of the sub- 

 genus Barhatia. Dr. Dall, in 1898^ thought 

 the species invalid, and that the type was 

 probably a shell of Area Candida that had 

 grown in a Lithodomus burrow. But in his 

 Peruvian catalogue, 1910, he listed the species, 

 referring it back to Cuming's shell and placing 

 it in the subgenus Barhatia. 



Mr. Axel Olsson, while at Bucaru, Los 

 Santos Province, on the western boundary of 

 Panama Bay, in 1921, was so fortunate as 

 to find a single valve which is the sole ex- 



1 Froc. Zool. Soo. London, p. 16, 1833. 



2 Conch. Icon., Area, pi. 12, f. 76, 1844. 



3 Trans. Wagner Inst. Sci., 3, pt. 4, p. 615. 



