 Complete the following phrase:  After five weeks only, the construction works had to be halted when the granite stones for the spiral stairs were missing. When the shipment arrived, a number of workers went on strike and refused to set foot on the dull island. Yet the remaining workers and some additional auxiliary hands were able to finish the brick building until November 1874, and to install the first order Fresnel lens with its Argand lamp of five wicks. The lens had been displayed at the 