The year 1869 was kinder to the engineers, and great headway was made. The men were able to make their first landing on the rock as early as March 25, and it was accessible up to October 29, when all forces withdrew from the scene for the winter. During this period sixty landings were effected, while heavy supplies of masonry and other materials were shipped to the site. The masons took up their permanent residence in the barrack on April 26, and did not leave it until September 3, while they were able to squeeze in 113 days of toil, with a welcome rest from their labours on Sundays. The excavations for the foundations were completed speedily, and on June 24 the erection of the tower was commenced. The stones were brought ready for setting in position, and were laid so rapidly that by the end of the month two courses were completed and the third had been well advanced. Then came a temporary setback. A blusterous summer gale sprang up, and the sea, after assaulting the rock for two days, succeeded in leaving its mark. The crane and other tackle at the landing-stage were washed away, while fourteen stones laid in the third course were uprooted, of which eleven were seen no more. The water in this case had to leap upwards for 35½ feet, while the stones which it carried away weighed 2 tons apiece, and were firmly joggled, so that the wrench which displaced them must have been terrific indeed. If a summer gale could wreak such damage, what was the dreaded equinox likely to achieve? The engineers were so much impressed that they thereupon made assurance doubly sure by effecting a modification of the original plans. When the work was commenced, it was intended to take the solid part of the tower up to a height of 52 feet 10 inches above high-water. The effects of this summer gale induced them to continue the solid section a further 11½ feet, so that the entrance level is 64 feet 4 inches above high-water mark. The result is that the solid base of the Dhu-Heartach tower weighs no less than 1,840 tons--more than one-half the total weight of the structure--and is executed throughout in massive blocks of grey granite. The tower contains six floors above the entrance hall, these, on ascending the spiral staircase, being as follows: oil-store, kitchen, provision-store, bedroom, dry-room, and light-room. The masonry part of the work was completed by the end of the season of 1871, and the first-order dioptric, fixed, white light was exhibited on November 1, 1872. The focal plane, being 145 feet above the water-level, has a range of eighteen nautical miles. The total cost of the work was £76,084, or $380,420, of which sum the shore station was responsible for £10,300, or $51,500.