New Standard,

or Roche dry cell. This cell possesses remarkable recuperative powers and low internal resistance. Made in many sizes, the best suited for medical coils is No. 2; dimensions, 5⁷∕₈ × 2⁷∕₁₆ inches. For heavier work the No. 5, 6 × 2⁹∕₁₆ inches, and known as the Navy Standard, is recommended. A convenient size for portable medical coils is No. 3, 3¾ × 1⅞ inches, taking up very little room, yet giving a large output. Two of these latter cells enclosed in the coil case will give with a suitably wound primary (No. 18 to 20 B & S) as strong a current as can be used in electrotherapy. For Ruhmkorff coils cells Nos. 6 and 7 (6 × 3 inches and 7 × 3 inches) furnish a most desirable battery for all work not needing the constant operation of the contact breaker, such as wireless telegraphy, gas-lighting, etc. They will do service on X-ray work, but the writer prefers a storage cell or the copper oxide types. The E. M. F. of the above cells is one and six-tenths volts, and current from 9 amperes to the No. 7 size, which gives 24 amperes on short circuit.