DEC. 4, 1921 SCIENTIFIC NOTES AND NEWS 499 



ing, astronomical observation, and directional wireless telegraphy. Dead 

 reckoning involves the measurement of air speed, ground speed, heading, 

 drift, and the amount and direction of the wind. The chief difficulty in this 

 method of navigation arises from the fact that the motion of the craft over 

 the ground is due to the resultant of the air velocity of the craft and the effect 

 of the wind, the latter being often difficult to determine. Instruments have' 

 been developed to measure directly or indirectly all of these quantities. 



In general principles marine and aerial navigation by astronomical ob- 

 ser\'ations are practically identical. The sextant is the universal instrument 

 used for observation on the celestial bodies in both cases. In the air, how- 

 ever, it often happens that no horizon is available to furnish a reference line 

 and it is then necessary to use an artificial horizon of some type, bubble, 

 pendulum, or gj^oscopic. Consequently, sextants with these horizons at- 

 tached are commonly used in aerial navigation. It is worthy of notice that 

 the aerial navigator often has available natural horizons which are never 

 visible from the surface of the sea. The top surface of the haze lying over 

 the ocean and flat layers of clouds often furnish excellent horizons. 



The radio direction finder can be used in the air to determine the position 

 of the craft by measuring the directions in which radio waves from the craft 

 reach two or more fixed stations or radio waves from the fixed stations reach 

 the craft. 



H. H. KiMBAivE, Recording Secretary. 



SCIENTIFIC NOTES AND NEWS 



THE PUEBLO BONlTO EXPLORATIONS 



Mr. Neil M. Judd, curator of American archeology, U. S. National Mu- 

 seum, returned to Washington recently after having been occupied in New 

 Mexico for more than five months as director of the National Geographic 

 Society's Pueblo Bonito Expedition. Pueblo Bonito is one of the largest 

 and best preserved prehistoric ruins north of Mexico. The Society has 

 obtained a permit from the Department of the Interior and it is expected 

 that the ruin can be wholly excavated within five years. No public notice 

 has yet been issued as to the results of this first season's explorations but it 

 is understood that the expedition was entirely successful both from the view- 

 point of excavations actually completed and from the amount of data re- 

 covered. 



A unique feature of this newest National Geographic Society expedition — • 

 one which has created considerable favorable comment among American 

 men of science — is a proposed series of annual conferences at Pueblo Bonito 

 to which specialists in the various humanistic sciences will be invited. The 

 first of these symposiums, held last August, was attended by archeologists 

 and agriculturists; geologists, botanists, and soil experts will be present at 

 next year's meeting. The willing cooperation of these gentlemen — leaders 

 in their respective fields of research — has made it possible to attack the 

 problem presented by the marvelous ruins of Pueblo Bonito on a scale not 

 thought possible heretofore; their combined efforts should result in a very 

 distinctive contribution to the history of ancient America. 



NOTES 



The following lectures have been given recently in the Bureau of Standards 

 Physics Club series on the physics of the Earth: Monday, October 31, WiL- 



