212 Selenography : its Past, Present, and Future. (April, 
heliometer. This preliminary examination was carried on 
by Dr. Wichmann, in 1847-48, who, after a careful investi- 
gation of the problem to be determined, applied the results 
of 50 measures with the Konigsberg heliometer, in 1844-46, 
to deduce the real libration. The results obtained by 
him were still more inconclusive than those arrived at by 
Nicollet; Wichmann’s conclusion being that the real libra- 
tion of short period could not exceed 10’ of selenographical 
longitude, and probably not 7’; but as to its exact amount, 
the observations failed to afford any satisfactory informa- 
tion. 
Though Wichmann’s individual measures were con- 
siderably superior to those of Bouvard and Nicollet, yet 
their small number, only 44 separate results, and the short 
period of 14 months in which they were made, with the 
irregular interval between them, renders them inferior as a 
series for this purpose to those of Bouvard and Nicollet, 
whose 174 measures were spread over a period of 4 years, 
and, commenced in 1806, extend to 1820. The uncertainty 
with respect to the amount of the real libration of the moon 
remains, therefore, as great asever. The value obtained by 
Wichmann for the inclination of the lunar equator to the 
ecliptic was I° 32’ 9”, or over 3’ greater than resulted from 
Nicollet’s investigation; and this discrepancy between the 
results obtained by the two investigators adds much to the 
uncertainty attending the whole question. Incidental to 
his investigation, Wichmann found for the position of 
Mosting A, longitude 5°13’ 23’, latitude 3° 10’ 55”, and 
that Burckhardt’s value of the moon’s semi-diameter was 
considerably too small. The determination of the problem 
of the real libration of the moon still required to be performed, 
and as Wichmann observed, it must be based on a con- 
siderable number of observations; not less than two hundred 
at regular intervals appears suitable, and should extend over 
at least three years. 
Schmidt devoted his attention mainly to the produétion of 
a lunar map that should adequately show the true details of 
the lunar surface which he recognised Madler’s failed to do, 
though representing most faithfully the greater formations. 
For this purpose he determined that a map 75 inches in dia- 
meter would be the smallest adequate size, being four times 
the area of Madler’s, though the results show even this to be 
too small for this purpose, producing too much crowding to be 
desirable. During his work, Schmidt has made over a 
thousand drawings, and three times as many height 
measures—but it is understood few (if any) measures of 
