14 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1916. 



iiegie Institution's archeological expedition to Central America under the able 

 direction of Sylvanus G. Morley. Tlie worli of exploring and studying in detail 

 the remarliable remains of the ancient Mayan culture was vigorously carried 

 forward. An especial object of the expedition was tlie discovery of additional 

 inscriptions embodying glyphic dates, for it is the dates, now read with facility, 

 which furnish the skeleton of Maya history. 



Among the ancient cities visited while the writer was associated with the 

 expedition were Antigua, the ancient Spanish capital of the kingdom of 

 Guatemala, built on the site of a prehistoric city ; the extensive ruins of the 

 ancient city of Iximache, near the site occupied to-day by the capital of 

 Guatemala, Guatemala City ; the ruined city of Quirigua in eastern Guatemala, 

 the subject of much scientific interest during recent years; and the ruins of 

 Copan, in Honduras, perhaps the most remarkable of all the American monu- 

 ments of antiquity. 



Especial attention was given by the writer to the ^ collection of data and 

 drawings to be utilized in preparing panoramic views of the several cities 

 visited, and every effort was made to obtain information regarding the techni- 

 cal methods employed by the ancient builders. The quarries from which the 

 stone was obtained were too deeply buried in tropical vegetation to yield up 

 their story without extensive excavation and the methods employed in dressing 

 and carving the stone remain in large part undetermined. Certain chipped and 

 ground stone implements that could have served in dressing the stones used in 

 building were found in numbers, but the story of the carving, especially of the 

 very deep carving of the monuments of Copan, remains unrevealed. Although 

 it is thought that stone tools may have been equal to the great task, it is 

 believed by some that without bronze the work could not have been done. 

 There are, however, no traces of the use of bronze by the Central Americans. 



The monuments are on a grand scale and great skill and excellent taste are 

 manifest in their embellishment, the whole giving evidence of a state of 

 culture advancement unsurpassed in any other part of aboriginal America. 



STUDY OF NOCTURNAL, RADIATION. 



Several grants from the Hodgkins fund have been made to Prof. 

 Anders Angstrom during the past few years to enable him to carry- 

 on researches on the radiation of the atmosphere, particularly noc- 

 turnal radiation. The results of observations made by him in 

 Algeria in 1912 and in California in 1913 were embodied in a 

 pamphlet published by the Institution in 1915. In this pamphlet he 

 summarizes his work as follows: 



The main results and conclusions that will be found in this paper are the 

 following. They relate to the radiation emitted by the atmosphere to a radiat- 

 ing surface at a lower altitude, and to the loss of heat of a surface by radiation 

 toward space and toward the atmosphere at higher altitudes. 



I. The variations of the total temperature radiation of the atmosphere are 

 at low altitudes (less than 4,500 m.) principally caused by variations in tem- 

 perature and humidity. 



II. The total radiation received from the atmosphere is very nearly propor- 

 tional to the fourth power of the temperature at the place of observation. 



III. The radiation is dependent on the humidity in such a way that an in- 

 crease in the water-vapor content of the atmosphere will increase its radiation. 

 The dependence of tbe ve^HXiUon on the water content has been expressed by 

 an exponential law. 



