Germanium (element), metal flashing on axle of cart
鍺 centers on the element germanium, a rare metal. The historical meaning of metal flashing on a cart axle is a separate, obscure technical sense.
鍺 combines 金 (metal) with 者, which likely contributes the sound. The character was originally used for a metal part on a cart axle, and later adopted for the element germanium.
The left side 金 means metal, and the right side 者 looks like a person. Imagine a person-shaped piece of germanium metal, or a metal axle part shaped like a person.
For タ, imagine a cart axle made of tantalum (another metal) that sounds like 'ta': tantalum -> タ, and the metal part is on the axle.