@article {Ballard1976b,
	title = {{Window on Earth{\textquoteright}s interior}},
	journal = {National Geographic Magazine},
	volume = {150},
	year = {1976},
	pages = {228{\textendash}249},
	keywords = {HOV Alvin (Human Occupied Vehicle)},
	issn = {0027-9358},
	author = {Ballard, R D}
}
