to the westward are to be seen the outposts of the Tucson Mountains, rugged hills of volcanic origin. On the more gradual northerly face of one of these, on a shoulder of gentle slope, stands the laboratory, a building appropriately constructed of the volcanic rock. The style is simple and well adapted to the climate. The thick stone walls heat slowly, particularly as they are for the most part protected from the direct rays of the sunlight by an overhanging roof. This latter is so constructed as to form a large ventilated air chamber, itself a protection from the effect of intense insolation as well as affording comfort to the occupants by modifying the strong light.
The form of the building is in the shape of the letter L, with the longer outer elevation facing the north. The dimension and disposition of the space within are indicated upon the accompanying plan. The windows are abundant, and when open to the brisk winds allow a current of air throughout the building which makes one forget the heat. About this factor much misapprehension is abroad. To be sure, the mercury stands high, and a registration of 100-105° F. is not at all unusual; occasionally it is even higher, and doubtless if one did not forget to look at the instrument, still higher temperature could be discovered. Fortunately, this is just what one does. There is so little discomfort attendant upon the heat that it is usually quite disregarded, a condition happily due to the low relative humidity, which on many occasions during six weeks in July and August of this year ran down as low as 7 per cent. The only feature of discomfort to some persons is the intense illumination, and one may require dark glasses, although I personally found no discomfort even upon the mesa. On
