Wright, Helen2015-07-032015-07-0319571957b14725769https://hdl.handle.net/2144/11651Includes 9 figures and 20 tables. Thesis (M.S.)--Boston University Please note: there's a discrepancy between the thesis itself, which claims 1955 as the submission date, and the library records, which claim 1957.en-USBased on investigation of the BU Libraries' staff, this work is free of known copyright restrictions.Thesis/Dissertation