In Prussia also, as we learn from a contemporary, the electric light at the Mechernich Mines has now had a fair trial for more than three years, and has proved a complete success. The expectation that it would both facilitate the operations and increase their security, has fully been realised, and an extension of the plant is now being carried out. An open working two thousand feet long, one thousand feet wide, and over three hundred feet deep, in which three hundred men and twenty horses are continually occupied, was first to be supplied with the electric light, and it was a question whether arc lamps would answer for this purpose in the smoky atmosphere caused by blasting operations. For the first experiments, arc lamps of three thousand and one thousand candles were used, with the positive carbon in the lower holder. The effect was brilliant, yet the light did not penetrate the white smoke cloud which collects at the upper wall immediately after the shot. But as the smoke settles within ten minutes, it was thought advisable to acquiesce in this interruption of a few minutes, and to use smaller lamps of three hundred and fifty candles, which proved quite efficient. Of these, there are ten in use, with about ten thousand feet of lead cable, the cable being partially elastic, as the lamps with their wires have to be removed when the blasting is to take place. The lamps were originally supplied with hexagonal lanterns with obscured glass to protect the eyes of the miners. The glasses were, of course, soon broken, but no complaints are said to have been made about the naked electric lights.