w 
1797+] 
placed that the radius of each would 
unite in one common centre, which is 
that of the lunar globe itfelf. 
Befides the evident ufe of an accurate 
delineation of the moon for aftronomical 
purpofes, particularly for the obferva- 
tions of lunar eclipfes, it cannot but be 
confidered as an object of great curiofity, 
that we fhould have an authentic record 
of the appearance of this our fecondary 
planet at a certain period ; for although 
the face of the moon has not appeared to 
be fubjeét to much change, fince the in- 
vention of the telefcope has given us the 
means of accurately inveftigating it, yet 
there are ftrong reafons for fuppofing 
that it is not abfolutely immutable ; nor 
is it poffible to fay how precious, in fu- 
ture times, fuch a reprefentation as this 
may become. 
_ Hevelius, the diligent obferver of the 
lunar phales, at the end of his Scleno- 
graphia, published in 1647, has ftrongly 
recommended fuch a globe ay this of Mr. 
Ruffell’s ; but we do not find any at- 
tempts were made towards its execution 
{though fo much defired by that great 
man, who fpoke of its utiliry) until the 
year 1745, when we are told that it was 
begun, and for feveral years purfued, by 
that moft eminent aftronomer, Tobias 
Mayer. The editor of his pofthumous 
works obferves, refpecting thefe intended 
luvar globes, “that it may pollibly af- 
ford potterity fome confolation, though 
indeed, but fmall, that the work was 
not obitructed by the death of Mayer ; 
but that being engaged in other difcove- 
ries, and for reafons it would concern 
but few to have related, that learned 
man had laid it afide a long time betore 
his death ;‘and, indeed, in fuch a man- 
ner, as it is related to me by his friends, 
that he expreffed himfelf much difpleated 
if any: one enquired after his lunar 
globes.” Vol. I. page 105. Appendix. 
The advantages which the lunar globe 
has over common prints or drawings of 
the moon, were confidered by Hevelius 
and Mayer, to be very great, and this 
opinion will appear the more reafonable, 
3f we confider that, while a flat reprefen- 
tation deferibes the moon only at one 
given moment, from which it is conti- 
nually deviating, the lunar globe repre- 
fents it at all times, and under all cir- 
cumftances. It will be difficult to fay 
hew feldom the moon can return to that 
ftate in which it will have perfectly the 
fame appearance as in any former in- 
ftance. Suppole an abfolutely mean ftate 
Of libration is enquired aiter ; the moon’ 
New Patents —Mr. Ruffell’s Selenographia. 
143 
muft not only be. in the line of apfides 
and of the nodes, but in the fame point 
of the ecliptic, or in that part of that 
moon’s orbit which is diametrically oppo- . 
fite ; for it can only happen at that time 
when the points of the lunar axes are in 
the plane of the viltble heimifphere of the 
moon; a concurrence of circumftances 
which many centuries together may not 
prefent us with; and the difficulty is, 
greatly increafed, by its being required 
that, to be pertectly in an apparent mean. 
ftate of. libration, the earth muft pretent 
the fame point of the equator to the moon, 
at the fame time when thofe other cir- 
cumfiances of her fituation may concur ; 
the diurna! libration or parallax being 
itfelf very confiderable. If it be ob- 
jected, that when the micrometer is form- 
ing triangles from the moon's furface, a 
fmall miftake may caufe much incorrect-~ 
nefs between thofe parts which are near 
the general margin or boundary of the 
moon ; it fhould. on the other hand, be 
confidered, that no greater error can arife. 
from hence than in the firft inftance, 
which, with good management, will be 
very inconfiderable, and not really appa- 
rent; becaule the globe of the moon is 
viewed in the fame manner as the moon 
itfelf. But the above cbjcétion will, in 
faét, be applicable to any reprefentation 
of the moon whatever. “The author fuy- 
gefts, that, as the libration gives diffe- 
rent views at different times, from hence 
there is an ability of corre€ting fuch mif- 
takes when difcovered, which the other 
means of reprefenting the moon’ does not 
{fo well allow: This might be demon- 
firated ; but a little reflection will pre- 
vent its neceflity. To be abfolutely cer- 
tain that drawing of the moon in sland 
is correct, we muft wait until the moon 
itfelf is in the fame ftate of libration, to 
compare it with the print or drawing ; 
but the lunar globe, being viewed with a 
telefcope, at the proper diftance, it may 
be compared with the moon at apy time, 
and its merits cr demerits may thus be 
directly known. Many agreeable as well 
as ufeful experiments can be made dur- 
ing fuch a comparifon ; but, for the fake 
of brevity, the defcription muft be here 
omitted. 
Upon the globe of the moon are faintly 
marxed three great circles, the one ho- 
rizontal, the other two vertical; that 
which is horizontal reprefeuts the equa-_ 
tor, which is placed upon that {pox of the 
moon named Cen/ormmus, and runs within 
three degrees north latitude of Gemaldus, 
The fecond fs the prime meridian, which, 
i pailing 
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