13; in this arrangement the needle strikes against small tubes formed of tin-plate.
The annual average value maybe put at not quite £2,000,000, machinery and tin-plate being a long way the most important items. There is further a small transit trade through Transcaucasia from Persia to the value of less than half a million sterling annually, and chiefly in carpets, cocoons and silk, wool, rice and boxwood; and further a sea-borne trade between Persia and Caucasian.
The slits may be cut out of tin-plate, and half covered by mica or " microscopic glass," held in position by a little cement.
There are, however, differences of treatment in detail, because copper is more malleable and softer than tin plate.