IO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



analyzed for us by Dr. Merrill of the United States National 

 Museum, who writes : 



Dr. Pogue has reported on the dust left by you this morning as being com- 

 posed of fragments of volcanic glass, quartz, feldspar and kaolin. Volcanic 

 glass is a common constituent of volcanic dust, as is also feldspar. Quartz 

 would occur only rarely, and kaolin scarcely at all. On account of the 

 decomposed condition of much of the glass, and the presence of kaolin, we 

 are both of us inclined to regard the dust as probably from the plains, and 

 not as derived directly from the volcano, although the glass would suggest an 

 ultimate volcanic origin. 



DECREASE OF HEAT AVAILABLE TO WARM THE EARTH 



In the passage of the beam of sunlight from the outer limit of the 

 atmosphere to the soil, losses of energy occur in the direct beam as 

 follows : ( i ) Absorption by the gases and vapors of the atmosphere, 

 principally in the infra-red water-vapor bands. (2) Scattering 

 of light towards the ground from the direct solar beam by the mole- 

 cules and dust particles of the atmosphere, thus producing the light 

 of the sky. This loss in the direct solar beam is made up to us by 

 the sky-light. ( 3 ) A fraction of the solar beam is scattered by the 

 molecules and dust particles of the air in such a direction as to go 

 out to space, and thus be lost to the earth for heating purposes. To 

 this may be added the quantity of radiation (if any) which is 

 absorbed in the higher atmosphere. 



The question arises how much the third loss, by diffuse reflection 

 and scattering to space and higher atmospheric absorption, was 

 increased owing to the presence of the dust cloud of 1912. It is 

 not possible to determine this loss by direct measurements. How- 

 ever, knowing the solar constant of radiation, the intensity of the 

 direct solar beam at the earth's surface, the intensity of the sky 

 radiation, and the quantity of absorption by atmospheric vapors, the 

 loss by high atmospheric absorption and by reflection of the atmos- 

 phere to' space may be approximately computed. We obtain the 

 value of the solar constant of radiation, the intensity of the direct 

 solar beam at the earth's surface, and the loss of radiation by 

 absorption in the vapors of the lower atmosphere, on each day of 

 observation. In order to determine the total intensity of the sky 

 radiation Mr. Abbot devised and constructed at Bassour two pieces 

 of apparatus, and made measurements for this purpose. 



The first contrivance was a bolometer with a somewhat wide 

 receiving strip. This bolometer was made with a wooden case, and 

 rough interior construction, but it was found to answer the purposes 



