four o’clock in the evening
The hole was made on the point of the shore , slanting , so that it should meet a much lower level than that of the water of the lake . In this way the explosive force , by scattering the rock , would open a large place for the water to rush out . The work took some time , for the engineer , wishing to produce a great effect , intended to devote not less than seven quarts of nitro-glycerine to the operation . But Pencroft , relieved by Neb , did so well , that towards four o'clock in the evening , the mine was finished . Now the question of setting fire to the explosive substance was raised . Generally , nitro-glycerine is ignited by caps of fulminate , which in bursting cause the explosion . A shock is therefore needed to produce the explosion , for , simply lighted , this substance would burn without exploding .