ON THE CHANGES OF THE MOON’S SURFACE. 517 
does not admit of this casy change of position may serve for other astrono- 
mical purposes ; for examinations of the moon’s surface it is useless. For 
even the largest refractors means may be devised to effect this ; but the great 
reflectors are mostly too unwieldly. Mechanics must contrive in this respect 
new means that the observer may be placed in a position to manage the great 
instrument in any direction that may be desired without extreme fatigue. 
For, besides that only under these circumstances all the moon’s phases can be 
used, it is often necessary to keep an object in view for many successive 
hours, in order to catch all its peculiarities. But, lastly, the carrying out 
completely the representation of an extensive moon landscape, or even of the 
whole visible hemisphere, is so comprehensive a task that it cannot be ex- 
pected from a single individual. W. Struvé, when he had set up the Dorpat 
refractor, thus expressed himself :—‘“ He who would delineate the moon with 
this telescope, must relinquish every other astronomical work ; for the details 
would be too many.” And it must be taken into consideration that the map- 
ping forms but a part of the labour here demanded, and that extended calcu- 
lations of the most varied kind must be made before and during the mapping; 
and thus we arrive at the conclusion that the greatest labour of an indivi- 
dual cannot suffice, but many must participate in the work. If, however, 
anything is to be gained by such united observation, the globe of the moon 
must be arranged by degrees of latitude, for only in this manner would its 
every phase be used by all employed,—a long and troublesome method, so 
that it might appear to many that the results would not be worth the trou- 
ble; but if we wish to become fully acquainted with the natural proportions 
of our satellite, we have no other choice. What has lately been observed in 
the crater Linné proves at all events that there real changes have taken place, 
and that too under circumstances even visible to us. Since Linné (by my 
work commenced thirty-eight years since) formed a chief point in the trigo- 
nometrical chain, I was enabled to give the proportionately exact infor- 
mation, which was desired from me on different sides. The occurrence of 
perceptible changes is therefore for the first time proved ; but equally remark- 
able is the circumstance that these events are rare ; for in seven years’ occu- 
pation with the moon’s surface I never met with such before, neither have 
Lohrmann and other careful observers of that time. 
Since, then, no doubt can be entertained that in such a case everything 
depends on being able to criticise how such an object appeared formerly, so 
might a possibly exhaustive representation and description of all the objects 
visible to us on the moon’s surface be the fundamental conditions of further 
intellectual advance. Photography will be able in many respects to facilitate 
the labours of which we have above spoken; undoubtedly our incipient hopes 
went much further ; but Uranology must rejoice in this new resource ; never- 
theless photographic representations of the moon cannot arrive at the details 
which an experienced eye and a large telescope can obtain; and in this case 
everything depends on the most exact representation of these delicate details. 
For the greater ring-mountains, plateaux, and chains of mountains belong to 
an epoch of formation very long past, and the present time does not dare to 
hope to perceive any changes in its general configuration ; and yet an occur- 
rence of which we are able to obtain knowledge is of the utmost importance. 
The crater Linné, which has hitherto offered the only authentic example of an 
admitted change, shows a diameter of 1:4 geographical miles, or six English 
miles ; and it appears to us only under an angle of 53 seconds. We can 
hardly dare to expect still greater and more extensive occurrences, and a 
considerable time will elapse before one will be able to give a comparative 
