Please go through this excerpt from "The Story of My Life" by Helen Keller:
The hands of those I meet are dumbly eloquent to me. The touch of some hands is an impertinence. I have met people so empty of joy, that when I clasped their frosty fingertips, it seemed as if I were shaking hands with a north east storm.
I understand the literal meaning of dumbly eloquent here. The word eloquent means fluent or persuasive in speaking or writing. So dumbly eloquent means the speech or literature are so persuasive and fluent that addresses all your questions and make you speechless. Eloquent relates to speech and writing. However, Helen Keller was unable to see and hear, and could only perceive by her touch. How can someone who cannot see and listen feel the some attribute which can be perceived by seeing or hearing only? How does eloquent fit in this context? What is the exact meaning of the phrase dumbly eloquent in this context?