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Cincinnati Society of Natural History. 



To know now much may be achieved with the simplest instrumental 

 appliances, we need but read the description of the Portable Dial, of 

 Ferguson, given in the Encyclopsedia Britannica, where you will see that 

 by means of a pasteboard card and a simple plumb-line — which by the 

 way is one of the most exact lines of reference the most refined as- 

 tronomers can obtain — with these simple means you can work out five 

 valuable astronomical problems. 



As, I. To find the hour of the day. 



II. To find the time of the sun's rising and setting. 

 To find the sun's declination. 

 To find what day the sun enters a "Sign." 

 To find the meridian altitude of the sun. 



In order to demonstrate what scientific skill the Mexicans displayed in 

 order to make accurate observations, on the celestial bodies, I herewith 

 call your attention to the drawing of an astronomical observatory, which 

 you will find in Lord Kingsborough's works, No. 72, Plate 24, Vol., IY, 

 Wm. Dupaix's collection. (Fig. 2.) 



III. 

 IV. 



V. 



/ / 



Q; 



i \ 

 ) \ 





■ 













s K 



1 ^ ___ ____ 









\B V 6 V 18 V 



Figure 2.— MEXICAN OBSERVATORY.— From Lord Kingsborough. 



Main chamber square. S-N — Tubular passage running north'and south O — Passage run- 

 ning east and west. C-Z — Vertical passage. V — Signifies a vara (32.9 inches). 



A rectangular chamber is seen, six yards wide and ten yards high, in- 

 tersected by two passages, at right angles and oriented ; one six feet high 

 by three feet wide, the other cylindrical, and only one foot in diameter, 

 its top six feet above the floor, and also due north and south, i. c, in the 



