Experiments employing a new type of regenerative direct‐current amplifier have shown that such equipment is unsuited for use, except, perhaps, in the laboratory. A successful system of amplification employing vacuum tube amplifiers and commutators for inverting and synchronously rectifying the resulting amplified alternating potentials is described. Thermocouple electromotive forces less than 10−9volt are readily indicated on a portable microammeter. The over‐all useful amplification with portable equipment exceeds 50,000.