Height of Cupola
What is commonly understood to be the height of a cupola is the distance from the bottom up to the lower edge of the charging-hole. When it is desired to obtain the best results when melting with hard coal or coke, the height for all cupolas up to fifty inches diameter should be at least five diameters; but when the diameter exceeds fifty inches, the height may be four diameters from the bottom to the lower edge of the charging-hole. See CUPOLA; CHARGING THE COMMON CUPOLA.
Helper is one who assists a mechanic or artist in the regular routine of his work, the more laborious and simple duties being his especial work, for which reason he is usually recognized as an unskilled laborer.