The chauffeurs of these desert-going cars are carefully chosen for their skill as drivers, their mechanical ability, and their endurance, most of them having served as airplane pilots or mechanicians during the war. Accompanying each car is an Arab guide who is presumed to be thoroughly familiar with the baffling topography of the regions to be traversed, though even the most experienced frequently encounter difficulty in getting their bearings, so completely is the aspect of the dunes changed by a violent sand-storm. In order to provide against emergencies, each car carries a tightly rolled tent on the roof and a week’s supply of emergency provisions. The cars originally used for the conquest of the Sahara were of quite a different type than the Renault. They were ten horse-power machines designed by André Citroen, the Henry Ford of France, and, in addition to the regular front wheels, were equipped with caterpillar treads, similar to those used on tanks and farm tractors. During the winter of 1922-23 a fleet of these cars crossed from Touggourt to Timbuktu, making the two-thousand-mile journey in twenty days. In October, 1924, a second Citroen expedition of eight cars traversed Africa from Algeria to the Great Lakes, where it divided, one group going on to Madagascar and another keeping southward to the Cape. The latter journey of fifteen thousand miles occupied nine months. Though it is generally admitted, I believe, that the tractor type of machine is able to negotiate country which would be quite impassable for the twelve-wheeler, it cannot attain the speed of the latter, its accommodations for passengers are far less commodious and comfortable, and, on account of the sharp stones which strew vast stretches of the central Sahara, its rubber-shod treads are quickly cut to pieces and cannot be replaced as readily as tires.