to Paris in 1877, Bartholdi concentrated on completing the head, which was exhibited at the 1878 Paris World's Fair. Fundraising continued, with models of the statue put on sale. Tickets to view the construction activity at the Gaget, Gauthier & Co. workshop were also offered. The French government authorized a lottery; among the prizes were valuable silver plate and a terracotta model of the statue. By the end of 1879, about 250,000 francs had been raised. The head and arm had been built with assistance from Viollet-le-Duc, who fell ill in 1879. He soon died, leaving no indication of how he intended to transition from the copper skin to his proposed masonry pier. The following year, Bartholdi was able to obtain the services of the innovative designer and builder Gustave Eiffel. Eiffel and his structural engineer, Maurice Koechlin, decided to abandon the pier and instead build an iron truss tower. Eiffel opted not to use a completely rigid structure, which would force stresses to accumulate in the skin and lead eventually to cracking. A secondary skeleton was attached to the center pylon, then, to enable the statue to move slightly in the winds of New York Harbor and as the metal expanded on hot summer days, he loosely connected the support structure to the skin using flat iron bars which culminated in a mesh of metal straps, known as "saddles", that were riveted to the skin, providing firm support. In a labor-intensive process, each saddle had to be crafted individually. To prevent galvanic corrosion between the copper skin and the iron support structure, Eiffel insulated the skin with asbestos impregnated with shellac. Eiffel's design made the statue one of the earliest examples of curtain wall construction, in which the exterior of the structure is not load bearing, but is instead supported by an interior framework. He included two interior spiral staircases, to make it easier for visitors to reach the observation point in the crown. Access to an observation platform surrounding the torch was also provided, but the narrowness of the arm allowed for only a single ladder, long. As the pylon tower arose, Eiffel and Bartholdi coordinated their work carefully so that completed segments of skin would fit exactly on the support structure. The components of the pylon tower were built in the Eiffel factory in the nearby Parisian suburb of Levallois-Perret. The change in structural material from masonry