H. A. Clarke is not an immediately recognizable author without more context or full name details. It's possible you could be referring to any number of authors with similar initials or names. If by H. A. Clarke you mean Hannah Allen Clarke, she was a 20th-century American author known for her books for young girls. However, if you are referring to another author, please provide more details so I can give you an accurate and helpful description. Without additional information, it isn't possible to determine which H. A. Clarke you're asking about.