At the beginning of the 20th century, complex rules governed the composition and number of candles to be used at Mass. Lighted candles of the correct composition (beeswax, with no more than a minimal admixture of other material, and usually bleached) were considered so essential that, if before the consecration they happened to go out (quenched, for instance, by a gust of wind) and could not be relit within fifteen minutes, the celebration of Mass had to be abandoned, and some writers maintained that even if the candles could be relit within that time, Mass should in any case be begun again from the start. Some of these rules were formulated only in the second half of the nineteenth and the beginning of the 20th century. The Roman Missal of the time continued to indicate merely that on the altar there should be "at least two candlesticks with lit candles" with a centrally placed cross between them ("Rubricae generales Missalis, XX - De Praeparatione Altaris, et Ornamentorum eius"). There is also a rule given in the same section of the Roman Missal - and still included even in the typical 1920 edition - that "a candle to be lit at the elevation of the Sacrament" should be placed with the cruets of wine and water to the Epistle side of the altar.