22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



We now come to the matter of the haziness encountered during our 

 observations on Mount St. Katherine, and by far the most serious 

 meteorological handicap found there. It is not remarkable that hazi- 

 ness should have occurred during the months from March to June, 

 but one would not expect to find it so intense at nearly 9,000 feet 

 elevation. Before visiting the mountain it was supposed that the pre- 

 vailing northwest and north winds sweeping down from the Medi- 

 terranean would carry all haze due to sand storms and other distur- 

 bances having their origin in the great Sahara Desert, to the south and 

 southwest of Mount St. Katherine. But from observations during 

 the spring months the above assumption was found to be incorrect. 

 The cirrus clouds nearly always moved from west toward east or from 

 southwest toward northeast. Such clouds probably lay from 10 to 20 

 kilometers above sea-level and hence showed that the prevailing winds 

 at such high elevations were moving from over the Sahara Desert 

 toward the Sinai Peninsula. Our observations showed that about 80 

 per cent of the haze storms moved in from the west or southwest, 

 and also that the haziness was usually fairly closely correlated to the 

 water-vapor content of the atmosphere, as indicated by the p/psc instru- 

 ment. At times, however, it was apparently due more to dust particles 

 and molecular scattering. It seems quite likely that fine dust particles 

 are carried to great altitudes during sand storms in the vast area of 

 the Sahara Desert, and being carried eastward or northeastward by 

 the prevailing winds at such high altitudes, finally, by force of gravity, 

 tend to settle, and in doing so, come in contact with the moisture-laden 

 north and northwest winds from the Mediterranean. These particles 

 act as nuclei for condensation, and the result is a haze particle of 

 considerable water-vapor content. This condensation occurs at times 

 at a much higher elevation than any mountains in Sinai or Egypt, and 

 hence no hope is had at such times to get above the haze. 



The one redeeming feature concerning the haziness is that our obser- 

 vations showed much more uniformity of conditions during observing 

 hours, particularly in the morning, than prevail at either the peaks of 

 Southwest Africa or at Table Mountain in California. The accompany- 

 ing graphs, which are taken from observations on average days in all 

 cases, clearly show the superiority of Sinai over Southwest Africa. 

 Hence, with such uniformity prevailing, even on very hazy days, 

 there is much hope that the solar transmission coefficients over Mount 

 St. Katherine can be quite accurately determined, in which case the 

 haze would not be fatal to good observations of the solar constant. 



In conclusion, in addition to the acknowledgments already cited, 

 may I express the thanks of the expedition to the following: to the 



