The dioptric apparatus, designed by Messrs. Stevenson, and manufactured by Messrs. Chance Brothers and Co. of Birmingham, is of a novel character, inasmuch as the condensing principle has been carried to a pronounced degree. The light characteristic is four brilliant flashes in quick succession every thirty seconds. The lenticular apparatus also includes the ingenious idea advocated by Mr. Thomas Stevenson, an earlier engineer-in-chief to the Northern Commissioners and perhaps the greatest authority on lighthouse optical engineering, whereby the light may be dipped during a fog. Thus, in clear weather the strongest part of the ray may be directed to the horizon, while in thick weather it can be brought to bear upon a point, say, four or five miles away. The flashes are produced by a revolving cage of straight vertical prisms, which enclose the fixed-light apparatus. This cage makes one complete revolution every minute, the rotary movement being secured through a train of wheels and a weight, which has a fall of 60 feet in a tube extending vertically through the centre of the tower, the mechanism being wound up once an hour by manual effort. The beam of light obtained by the aid of electricity is of intense brilliancy and penetration. Its equivalent in candle-power is somewhat difficult to determine, because the methods of calculation are somewhat arbitrary and misleading. By their own method of calculation, the engineers responsible for the installation rate it at 3,000,000 candle-power with one generator in use, and 6,000,000 candle-power when both are going. This is from 300 to 600 times as intense as the oil light which was superseded. By another method of calculation the beam is of 26,000,000 candle-power, while another principle of rating brings it to upwards of 50,000,000 candle-power. In clear weather the light has a range of twenty-two miles, being indistinguishable at a greater distance, owing to the curvature of the earth; but the flashes of light illuminating the clouds overhead may be picked up forty or fifty miles away. The total cost of electrifying the Isle of May light was £15,835, or $79,175; while the annual cost of maintenance is over £1,000, or $5,000. The most famous English electric lighthouse is that of St. Catherine’s, in the Isle of Wight. This point, like the Isle of May, has been a beacon for centuries. Its creation for this work even antedates its northern contemporary, because in the fourteenth century a chantry was built by a benevolent knight on the highest point of St. Catherine’s Downs, who furthermore provided an endowment for a priest “who should chant Masses and maintain a burning light at night for the safety of mariners.” But this protection fell into desuetude.