ON MAPPING THE SURFACE OF THE MOON. 15 



occasionally could see a shadow very black near the centre of Linnc'. Either 

 in the crater, or it might be the shadow of a very small peak, very white. 

 Several times distinctly seen on the W. jiart of the centre of Linne (not at the 

 edge), but no ajipearance of usual crater or shadow ; the shadow seen was a 

 black but not round spot, but longer N. and S." 



" 1866, Dec. 26. [Herr Schkidt.] Yon 12-lG Uhr. YorziigUch klare, ganz 

 stille Luft, so dass ich die stiirksten Oculare anwenden konnte. Die Phase 

 beriihrte den Westrand des Mare Serenitatis ; da y Posidonius, der Phase nahe, 

 Schatteu warf, und also nicht mehr als Lichtfleck erschien, konnte er 

 nicht mehr mit Linnd verglichen werden. Im Marc zahlte ich iiber 100 

 Crater, danmtcr nordwcstlich von Linnc deren siebeu fast in ciner Eeihc, die 

 schon Schroter am 27 fiissigon Reflector bemerkt liatte. Aber auch jetzt war 

 Linne ein gewohnlicher Lichtfleck von gcringer Augenfalligkeit. Yon 14|- 

 1(3 Uhr sail ich in ihm mit 500-600-maligen Yergrdsserung, einen ausserst 



(.r \ /BesselN 



~ I schiitzte, aber x=:[ ^" \> was 

 6-5/. V 6-5 / 



auf eiiien wahren Durchmcsser von 265 Toisen fiihrt. Entweder war cs der 

 Schatten eines sehr kleinen Hiigels, oder der llest des ehemals 5700 Toisen 

 breiten Craters. Die Hohe der >Sonne fiir diese Gegend war jetzt =15°-9." 

 Translation. — Dec. 2G. From 12'' to 16" particularly clear and perfectly 

 stiU atmosphere, so that I could use the most powerful ej'epieces. The ter- 

 minator was in contact with the western edge of the Mare Serenitatis. As y 

 Posidonius, being near fhe terminator, threw a shadow, it could no longer be 

 compared with Linne. In the Marc I coimted more than 100 craters, 

 several N.W. of Linne, seven of them almost in a row, which Schroter had 

 already noticed with the 27-feet reflector. But even now Linne was an ordi- 

 nary spot of light, but little conspicuous. From 14'' 30"" to 16** 0"* I saw in it 

 witia a power of 500-600 an extremely delicate black point, which I estimated 



(X \ /Besscl\ 



—^ I, but A'=i '. ~ I*, which indicates a real diameter of 265 



toises (1695 English feet). It was either the shadow of a very smaU hUl, 

 or the remainder of the crater, 5700 toises (36,449 English feet) wide. The 

 height of the sun at this region was 15° 9'. 



* As illustrative of Herr Schmidt's estimations ofheights the reader is referred to B. and 

 M.'s method, as described in ' Der Mond,' § 65, p. 98, a translation of which, by W. T. Lynn, 

 Esq., is as ibllows: — "To measure and calcidate the heights of all' the mountains in the 

 moon which, luider favourable circumstances, throw peroeijtible shadows, would not only 

 be inconceiyably tedious and troublesome, but, besides this, tlie desired degree of ac- 

 curacy would still, in the majority of cases, not be attained, because the shadows are too 

 short. But when an observer has acquired sufficient practice by repeated measurements 

 under different angles of illumination, he may use one measured mountain (selecting 

 one as high as possible) as a standard of estimation for others lying in its neighbour- 

 hood, especially when they are nearly the same distance from the terminator. Pos- 

 sessed of some practice in eye-estimations, he will easjly be able to find how many times 

 the length of a small shadow is contained in the greater one formed by the princiisal 

 mountain. Thus it was estimated on the 17th of March, 1834, that the shadow of tlie 

 N.W. wall of Egede was equal to J^ of the shadow of the wall of Eudoxus, the height 

 of which latter was determined by calculation to be 1627 toises. Egede is situated in the 

 neighbourhood of Eudoxus, and its distance from the terminator was then -J that of Eu- 

 doxus, so that approximately the height of its N.W. wall was^xAxl627=54toises above 

 the interior surface. In this, or a similar manner, have many of tlie elevations given in 

 the topographical description been determined ; those actually calculated according to the 

 above formula; are set down in § 07 following." 



Herr Schmidt, speaking of this method in a letter to Mr. Lynn, says, " Such estima- 

 tions are very accurate, and between hills of the height of 50-200 toises which have been 

 measured, differencesof elevation of 5 or 6 toises can, when close to the terminator, be sa- 

 tisfactorily and certainly estimated." 



