208 Selenography : its Past, Present, and Future. {April, 
laid down by practically eye estimations. Measures of the 
position of the principal objects upon the moon were there- 
fore requisite for further progress, and then the almost 
unknown smaller delait could be properly inserted. 
In 1824 appeared Lohrmann’s ‘‘ Topographie der Sicht- 
baren Mondoberflache,” comprising four se¢tions of what 
was intended to be a complete lunar map, 373 inches in 
diameter, divided into 25 sections, being the first detailed 
lunar chart based on scientific principles. As a foundation, 
employing a method devised by Encke, Lohrmann made a 
series of 150 good measures with a parallel wire micro- 
meter, on a 4% inch achromatic, of the distance of 21 spots 
from the limb, all the objects being within the area of his 
four sections, namely, from 12° east to 38° west longitude, 
and 12° south to 37° north latitude. Of these points of the 
first order, as they were termed, twelve, whose position rested 
on the results of from 8 to 12 measures, may be regarded as 
determined with fair accuracy, five based on from five to seven 
observations were not quite so satisfactory, whilst the re- 
maining five were founded on too few measures to be con- 
sidered of much value. ‘These measured positions were, 
however, far too few for the great area that rested on them, 
and few, if any, auxiliary points were measured. The 
section of his map, based on these results, was, however, a 
great improvement on all former charts, and constituted 
the first trustworthy delineation of the moon’s surface; it 
was therefore unfortunate that failing health prevented its 
ever being completed. In some points, however, Lohr- 
mann’s work was defe¢tive, asno height measures were made 
only those earlier made by Schroter with imperfect means 
quoted, and few formations had their dimensions measured. 
In 1837 appeared Beer and Madler’s *“‘ Der Mond,” founded 
on the results of observations made during the years 1830 to 
1837, accompanied by a complete lunar chart, in four quad- 
rants, on a scale of 374 inches to the lunar diameter. Asa 
foundation for their map, Madler, whom it is understood 
was the principal observer, made a series of gig direct mi- 
crometrical measures from the limb of the principal lunar 
points, adopting Encke’s system of computing the moon’s 
libration and reducing the measures. Rejecting 104 of these 
—principally the earlier—as discordant, imperfect, or doubt- 
ful, from the remainder, the position of 92 points were deter- 
mined, 7 being, however, points already chosen by Lohr- 
mann, whilst the position of each point rested on from 8 to 
10 measures. In constructing their map, as Beer and 
Madler combined Lohrmann’s results with their own, they 
