554 HEPOKT — 1902. 



degree of bodily motion of the resulting image the definition at any time and place 

 can be accurately and absolutely recorded. 



The increasing perfection of the optical image of a star testifies to the increas- 

 ing lack of damaging currents with reference to the object-glass used. It records 

 all the waves below a certain wave-leugth. JSirailarly the amount of bodily 

 motion registers all those above that length. The two taken together give 

 account of all the currents independent of the glass. 



(5. The Scale. — It is therefore necessary only to agree upon some size ot glass 

 for making the fundamental tests and then to reduce the results to any aperture by 

 relations which will be found set forth in a pamphlet by Mr. Douglas made at 

 this observatory entitled ' Scales of Seeing.' 



The most feasible size for comparison purposes seems the 6-inch aperture. 



The scale it is proposed to adopt is therefore as follows : — 



With a 6-inch glajsi — 



Disc and rings confused and enlarged. 

 '2 Disc and rings confused but not enlarged. 

 4 Disc defined ; no evidence of rings. 

 6 Disc defined ; rings broken but traceable. 

 8 Disc defined ; rings complete but moving. 

 10 Disc defined ; rings motionless. 



Synchronous determination of the amount of bodily motion of image in seconds 

 of arc. 



5. Expedition for the ascertahiing nf the best Location of Observatories. 



By Percival Lowell. 



In order to discover tlie best place or places for the location of telescopes iu the 

 future it i.s proposed to send observers furnished witli similar instruments and 

 identical instructions to all promising parts of the earth's surface. 



Two desert-belts girdle the earth in the sub-tropical regions of Capricorn and 

 Cancer, and from the meteorologic conditions there prevailing these belts offer the 

 greatest promise to the astronomer. In the northern hemisphere the belt shows 

 itself first in the Sahara of Africa, then in Arabia, then in the desert of Gobi, and, 

 crossing the Pacific, crops out again in Arizona and Mexico. Of these the two 

 with the greatest height for their plateaux are Arizona and Mexico and the desert 

 of Gobi. In the southern hemisphere we have the veldt of southern Africa, the 

 western part of Australia, and finally the west coast of Peru and Bolivia. Of these 

 the last is the highest and the Transvaal the next. 



With regard to these places Ave have the most systematic series of records from 

 Arizona, the next so from Peru, some slight knowledge of the Sahara, and next to 

 none of any other locality. 



Although the desert-belts promise the best, other localities widely different 

 should also be examined. Chief among these perhaps are the islands of the Pacific. 



It is desirable, therefore, to send out observers somewhat as follows : 



1. To the desert of Gobi. 



2, To the veldt of the Transvaal. 

 ■3. To the Samoan Islands. 



The observations made at these points could then be repeated elsewhere till 

 the earth's surface should be known from an astronomic point of view. 



Each observer is to be armed with a 6-inch glass, all the glasses to be made by the 

 same maker (for instance, Alvan Clark & Sons' Corporation), and to report according 

 to the proposed standard scale of ' seeing.' 



It is thus important that the said scale should be agreed to by astronomers 

 generally before the various expeditions start. 



