296 



REPORT — 1865. 



which are expressed in German miles. 

 This list in " Der Mond " is preceded by 

 a formula for computing the diameters 

 from observations, dependent on the 

 moon's distance from the earth, as ex- 

 pressed by parallax, the moon's altitude 

 above the horizon, and the position of 

 the object with regard to the visible 

 centre of the moon's disk. 



The computation of the heights of 

 mountains requires, according to Beer 

 and Madler's method, three measured 

 elements, viz., the length of the shadow, 

 the distance of the summit from the ter- 

 minator or boundary between light and 

 darkness, and also its distance from one 

 of the horns or the extremity of the 

 enlightened part of the moon north or 

 south. These measured data, combined 

 with the longitude and parallax of the 

 sun, and the longitude, latitude, aDd 

 parallax of the moon, enable the obser- 

 ver to determine the true length of the 

 shadow in parts of the moon's radius, 

 having previously ascertained two im- 

 portant angles, viz., that which the ter- 

 minator makes with the line joining the 

 horns, and that which measures the sun's 

 altitude above the horizon (at the moon) 

 of the object measured. After having 

 ascertained the length of the shadow in 

 parts of the moon's radius, it is not dif- 

 ficult to determine the height of the 

 object. 



Schroter has given, in his ' Selenoto- 

 pographische Fragmente,' numerous in- 

 stances of measured mountains, both iso- 

 lated and on the rings of craters, the re- 

 sults being expressed in Parisian feet. 

 Beer and Madler have given a list of 1095 

 measurements of heights expressed in 

 French toises, and Madler, on the small 

 map published in 1837, gives 236 ex- 

 pressed in Parisian feet. For the results 

 of the measurements converted into Eng- 

 lish feet two columns (9 and 10) have 

 been appropriated in Form No. 3. 



Two columns (11 and 12) are also 

 provided for brightness, or " Beflective 

 Power," one headed Estimated the other 

 Measured. The observer of the moon's 

 surface cannot fail to be struck, not only 

 with a great variety of tints in which 



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