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--------------------------              
,transcriber's note3                    
,words in ,italic are enclosed between  
underscores4                            
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----------------------------------------
--------------------------     ,,the    
,,sidereal ,,messenger                  
,,rivingtons      ,london      ,waterloo
 ,place      ,oxford      ,magdalen     
,street      ,cambridge   ,trinity      
,street   ,illustration3 ,,galileo',s   
,,broken ,,lens4  ,,exhibited ,,in ,,the
 ,,loan ,,collection ,,of ,,scientific  
,,apparatus ,,at ,,the ,,south          
,,kensington ,,museum1 #ahgf4  ,from a  
photograph of the ,science and ,art     
,department1 ,south ,kensington4        
,,the ,,sidereal ,,messenger      ,,of  
,,galileo ,,galilei      ,,and ,a ,,part
 ,,of ,,the ,,preface ,,to ,,kepler',s  
,,dioptrics      ,,containing ,,the     
,,original ,,account ,,of ,,galileo',s  

,,astronomical ,,discoveries4      ,a   
,translation with ,introduction and     
,notes      ,,by      ,,edward          
,,stafford ,,carlos1 ,m4,a4      ,,head 
,,mathematical ,,master ,,in ,,christ',s
 ,,hospital4      ,,rivingtons          
,,waterloo ,,place1 ,,london     ,oxford
 and ,cambridge     ,,mdccclxxx         
,,prefatory ,,note4   ,about five years 
ago ,i was engaged in preparing a       
catalogue of the ancient books which    
belong to ,christ's ,hospital4 ,one     
portion of these books consisted of a   
collection of ancient mathematical works
 presented at various times for the use 
of that part of the school which is     
known as the ,royal ,mathematical       
,foundation of ,king ,charles ,,ii4     
,amongst them were some well known by   
name to every mathematical student1 but 
which few have ever seen4 ,perhaps the  
most interesting of them all was a      
little volume1 printed in ,london in    
#afec1 containing ,gassendi's           
,explanation of the ,ptolemaic and      

,copernican ,systems of ,astronomy1 as  
well as that of ,tycho ,brahe1          
,galileo's ,sidereus ,nuncius1 and      
,kepler's ,dioptrics4 ,i found          
,galileo's account of his astronomical  
discoveries so interesting1 both in     
matter and in style1 that ,i translated 
it as a recreation from school-work4 ,i 
venture to think that others also will  
be interested in following ,galileo     
through the apprehension of his famous  
discoveries1 and in reading the language
 in which he announced them4            
,,introduction4   ,in #afji1 ,galileo1  
then ,professor of ,mathematics at      
,padua1 in the service of the ,venetian 
,republic1 heard from a correspondent at
 ,paris of the invention of a telescope1
 and set to work to consider how such an
 instrument could be made4 ,the result  
was his invention of the telescope known
 by his name1 and identical in principle
 with the modern opera-glass4 ,in a     
maritime and warlike ,state1 the        
advantages to be expected from such an  

invention were immediately recognised1  
and ,galileo was rewarded with a        
confirmation of his ,professorship for  
life1 and a handsome stipend1 in        
recognition of his invention and        
construction of the first telescope seen
 at ,venice4 ,in his pamphlet1 ,the     
,sidereal ,messenger1 here translated1  
,galileo relates how he came to learn   
the value of the telescope for          
astronomical research2 and how his      
observations were rewarded by numerous  
discoveries in rapid succession1 and at 
length by that of ,jupiter's satellites4
 ,galileo at once saw the value of this 
discovery as bearing upon the           
establishment of the ,copernican system 
of astronomy1 which had met with slight 
acceptance1 and indeed as yet had hardly
 any recommendation except that of      
greater simplicity4 ,kepler had just    
published at ,prague his work on the    
planet ,mars 7,commentaria de motibus   
,stell ,martis71 on which he had been   
engaged apparently for eight years2     

there he heard of ,galileo's            
discoveries1 and at length was invited  
by ,galileo himself1 through a common   
friend1 ,giuliano de' ,medici1          
ambassador of the ,grand-,duke of       
,tuscany1 ,cosmo de' ,medici ,,ii41 to  
the ,emperor ,rudolph ,,ii41 to         
correspond with ,galileo on the subject 
of these discoveries4 ,the ,emperor also
 requested his opinion1 and ,kepler     
accordingly examined ,galileo's         
,sidereal ,messenger in a pamphlet1     
entitled ,a ,discussion with the        
,sidereal ,messenger 7,florence1 #afaj74
  ,in this ,discussion ,kepler gives    
reasons for accepting ,galileo's        
observations--although he was not able  
to verify them from want of a           
telescope--and entirely supports        
,galileo's views and conclusions1       
adducing his own previous speculations1 
or pointing out1 as in the case of      
,galileo's idea of earth-light on the   
moon1 the previous conception of the    
same explanation of the phenomenon4 ,he 

rejects1 however1 ,galileo's explanation
 of the copper colour of the moon in    
eclipses4 ,kepler ends by expressing    
unbounded enthusiasm at the discovery of
 ,jupiter's satellites1 and the argument
 it furnishes in support of the         
,copernican theory4  ,soon after1 in    
#afaa1 ,kepler published another        
pamphlet1 his ,narrative1 giving an     
account of actual observations made in  
verification of ,galileo's discoveries  
by himself and several friends1 whose   
names he gives1 with a telescope made by
 ,galileo1 and belonging to ,ernest1    
,elector and ,archbishop of ,cologne4   
,kepler and his friends saw the lunar   
mountains and three of the satellites of
 ,jupiter1 but failed to make out any   
signs of the ring of ,saturn            
corresponding to the imperfect          
description of ,galileo4  ,kepler had   
previously published a treatise on      
,optics 7,frankfort1 #afjd74 ,he now    
extended it to the consideration of the 
theory of the telescope1 and explained  

the principle of ,galileo's telescope2  
he also showed another combination of   
lenses which would produce a similar    
effect4 ,this was the principle of the  
common astronomical telescope1 often    
called1 from this circumstance1         
,kepler's telescope1 though he did not  
construct it4 ,the account of ,galileo's
 later astronomical discoveries of      
,saturn's ring and the phases of ,venus 
is taken from the preface of this       
work4--7,kepler's ,dioptrics2 ,augsburg1
 #afaa47  ,in #afab ,galileo published a
 series of observations of solar spots1 
and in #afah some observations of three 
comets4 ,there exist also long series of
 minute observations of ,jupiter and his
 satellites1 continued to ,november     
#afai4--7;,galileo's ,works2 ,florence1 
#ahde47  ,further astronomical          
researches may have been hindered by    
failing sight4 ,one more astronomical   
discovery1 however1 that of the moon's  
librations1 was made as late as #afcg1  
and the announcement of it is dated     

8dalla mia carcere di ,arcetri40        
,galileo died ,january #h1 #afdb4   ,the
 following editions have been used for  
the translation3--  ,galileo's ,works4  
#a4  ,florence1 #agah4     #b4  ,padua1 
#agdd4     #c4  ,florence1 #ahdb-ef4    
,sidereus ,nuncius4      #a4  ,venice1  
#afaj4     #b4  ,london1 #afec4         
,kepler's ,works1 ed4 ,c4 ,frisch4      
,frankfurt a4 ,m41 #aheh-ga4            
,prodromus dissertationum mathematicarum
 continens ,mysterium                   
,cosmographicum de admirabili           
proportione orbium clestium4            
,tbingen1 #aeif4      ,astronomia nova  
7,commentaria de motibus stell          
,martis74 ,prague1 #afji4         ,,the 
,,sidereal ,,messenger      ,,of        
,,galileo ,,galilei         ,,the       
,,sidereal ,,messenger      ,,unfolding 
,,great ,,and ,,marvellous ,,sights1    
,,and ,,proposing ,,them ,,to     ,,the 
,,attention ,,of ,,every ,,one1 ,,but   
,,especially ,,philosophers ,,and       
,,astronomers1      ,,being ,,such ,,as 

,,have ,,been ,,observed ,,by           
,,galileo ,,galilei      ,a ,,gentleman 
,,of ,,florence1 ,,professor ,,of       
,,mathematics ,,in ,,the ,,university   
,,of ,,padua1      ,,with ,,the ,,aid   
,,of ,a      ,,telescope      lately    
invented by him1      ,respecting the   
,moon's ,surface1 an innumerable number 
of ,fixed     ,stars1 the ,milky ,way1  
and ,nebulous ,stars1 but especially    
respecting     ,four ,planets which     
revolve round the ,planet ,jupiter at   
different     distances and in different
 periodic times1 with amazing velocity1 
and which1 after remaining unknown to   
every one up to this day1 the           
,author recently discovered1 and        
determined to name the      ,,medicean  
,,stars4      ,venice #afaj4   ,,to     
,,the ,,most ,,serene  ,,cosmo ,,de'    
,,medici1 ,,the ,,second1  ,,fourth     
,,grand-,,duke ,,of ,,tuscany4   ,there 
is certainly something very noble and   
large-minded in the intention of those  
who have endeavoured to protect from    

envy the noble achievements of          
distinguished men1 and to rescue their  
names1 worthy of immortality1 from      
oblivion and decay4 ,this desire has    
given us the lineaments of famous men1  
sculptured in marble1 or fashioned in   
bronze1 as a memorial of them to future 
ages2 to the same feeling we owe the    
erection of statues1 both ordinary and  
equestrian2 hence1 as the poet#a says1  
has originated expenditure1 mounting to 
the stars1 upon columns and pyramids2   
with this desire1 lastly1 cities have   
been built1 and distinguished by the    
names of those men1 whom the gratitude  
of posterity thought worthy of being    
handed down to all ages4 ,for the state 
of the human mind is such1 that unless  
it be continually stirred by the        
counterparts#b of matters1 obtruding    
themselves upon it from without1 all    
recollection of the matters easily      
passes away from it4      #a            
,propertius1 iii4 #b4 #ag-bb4      #b   
,compare ,lucretius iv4 #hha3      ,dico

 animo nostro primum simulacra meandi   
,accidere1 atque animum     pulsare4    
,but others1 having regard for more     
stable and more lasting monuments1      
secured the eternity of the fame of     
great men by placing it under the       
protection1 not of marble or bronze1 but
 of the ,muses' guardianship and the    
imperishable monuments of literature4   
,but why do ,i mention these things1 as 
if human wit1 content with these        
regions1 did not dare to advance        
further2 whereas1 since she well        
understood that all human monuments do  
perish at last by violence1 by weather1 
or by age1 she took a wider view1 and   
invented more imperishable signs1 over  
which destroying ,time and envious ,age 
could claim no rights2 so1 betaking     
herself to the sky1 she inscribed on the
 well-known orbs of the brightest       
stars--those everlasting orbs--the names
 of those who1 for eminent and god-like 
deeds1 were accounted worthy to enjoy an
 eternity in company with the stars4    

,wherefore the fame of ,jupiter1 ,mars1 
,mercury1 ,hercules1 and the rest of the
 heroes by whose names the stars are    
called1 will not fade until the         
extinction of the splendour of the      
constellations themselves4  ,but this   
invention of human shrewdness1 so       
particularly noble and admirable1 has   
gone out of date ages ago1 inasmuch as  
primeval heroes are in possession of    
those bright abodes1 and keep them by a 
sort of right2 into whose company the   
affection of ,augustus in vain attempted
 to introduce ,julius ,csar2 for when he
 wished that the name of the ,julian    
constellation should be given to a star1
 which appeared in his time1 one of     
those which the ,greeks and the ,latins 
alike name1 from their hair-like tails1 
comets1 it vanished in a short time and 
mocked his too eager hope4 ,but we are  
able to read the heavens for your       
highness1 most ,serene ,prince1 far more
 truly and more happily1 for scarcely   
have the immortal graces of your mind   

begun to shine on earth1 when bright    
stars present themselves in the heavens1
 like tongues to tell and celebrate your
 most surpassing virtues to all time4   
,behold therefore1 four stars reserved  
for your famous name1 and those not     
belonging to the common and less        
conspicuous multitude of fixed stars1   
but in the bright ranks of the          
planets--four stars which1 moving       
differently from each other1 round the  
planet ,jupiter1 the most glorious of   
all the planets1 as if they were his own
 children1 accomplish the courses of    
their orbits with marvellous velocity1  
while all the while with one accord they
 complete all together mighty           
revolutions every ten years round the   
centre of the universe1 that is1 round  
the ,sun4  ,but the ,maker of the ,stars
 himself seemed to direct me by clear   
reasons to assign these new planets to  
the famous name of your highness in     
preference to all others4 ,for just as  
these stars1 like children worthy of    

their sire1 never leave the side of     
,jupiter by any appreciable distance1 so
 who does not know that clemency1       
kindness of heart1 gentleness of        
manners1 splendour of royal blood1      
nobleness in public functions1 wide     
extent of influence and power over      
others1 all of which have fixed their   
common abode and seat in your           
highness1--who1 ,i say1 does not know   
that all these qualities1 according to  
the providence of ,god1 from whom all   
good things do come1 emanate from the   
benign star of ,jupiter8 ,jupiter1      
,jupiter1 ,i maintain1 at the instant of
 the birth of your highness having at   
length emerged from the turbid mists of 
the horizon1 and being in possession of 
the middle quarter of the heavens1 and  
illuminating the eastern angle1 from his
 own royal house1 from that exalted     
throne1 looked out upon your most happy 
birth1 and poured forth into a most pure
 atmosphere all the brightness of his   
majesty1 in order that your tender body 

and your mind--though that was already  
adorned by ,god with still more splendid
 graces--might imbibe with your first   
breath the whole of that influence and  
power4 ,but why should ,i use only      
plausible arguments when ,i can almost  
absolutely demonstrate my conclusion8   
,it was the will of ,almighty ,god that 
,i should be judged by your most serene 
parents not unworthy to be employed in  
teaching your highness mathematics1     
which duty ,i discharged1 during the    
four years just passed1 at that time of 
the year when it is customary to take a 
relaxation from severer studies4        
,wherefore1 since it evidently fell to  
my lot by ,god's will1 to serve your    
highness1 and so to receive the rays of 
your surpassing clemency and beneficence
 in a position near your person1 what   
wonder is it if you have so warmed my   
heart that it thinks about scarcely     
anything else day and night1 but how ,i1
 who am indeed your subject not only by 
inclination1 but also by my very birth  

and lineage1 may be known to be most    
anxious for your glory1 and most        
grateful to you8 ,and so1 inasmuch as   
under your patronage1 most serene       
,cosmo1 ,i have discovered these stars1 
which were unknown to all astronomers   
before me1 ,i have1 with very good      
right1 determined to designate them with
 the most august name of your family4   
,and as ,i was the first to investigate 
them1 who can rightly blame me if ,i    
give them a name1 and call them the     
,medicean ,stars1 hoping that as much   
consideration may accrue to these stars 
from this title1 as other stars have    
brought to other heroes8 ,for not to    
speak of your most serene ancestors1 to 
whose everlasting glory the monuments of
 all history bear witness1 your virtue  
alone1 most mighty sire1 can confer on  
those stars an immortal name2 for who   
can doubt that you will not only        
maintain and preserve the expectations1 
high though they be1 about yourself1    
which you have aroused by the very happy

 beginning of your government1 but that 
you will also far surpass them1 so that 
when you have conquered others like     
yourself1 you may still vie with        
yourself1 and become day by day greater 
than yourself and your greatness8       
,accept1 then1 most clement ,prince1    
this addition to the glory of your      
family1 reserved by the stars for you2  
and may you enjoy for many years those  
good blessings1 which are sent to you   
not so much from the stars as from ,god1
 the ,maker and ,governor of the stars4 
,your ,highness's most devoted servant1 
,galileo ,galilei4      ,padua1 ,march  
#ab1 #afaj4     ,,the ,,astronomical    
,,messenger       ,containing and       
setting forth ,observations lately made 
with the aid     of a newly invented    
,telescope respecting the ,moon's       
,surface1 the     ,milky ,way1 ,nebulous
 ,stars1 an innumerable multitude of    
,fixed ,stars1     and also respecting  
,four ,planets never before seen1 which 
have been     named      ,,the ,,cosmian

 ,,stars4#c      #c ,the satellites of  
,jupiter are here called 8the ,cosmian  
,stars0     in honour of ,cosmo de'     
,medici1 but elsewhere ,galileo calls   
them     8the ,medicean ,stars40 ,kepler
 sometimes calls them 8the ,medicean    
,stars10 but more often 8satellites40   
,sidenote3 ,introduction4  ,,in the     
present small treatise ,i set forth some
 matters of great interest for all      
observers of natural phenomena to look  
at and consider4 ,they are of great     
interest1 ,i think1 first1 from their   
intrinsic excellence2 secondly1 from    
their absolute novelty2 and lastly1 also
 on account of the instrument by the aid
 of which they have been presented to my
 apprehension4  ,the number of the      
,fixed ,stars which observers have been 
able to see without artificial powers of
 sight up to this day can be counted4   
,it is therefore decidedly a great feat 
to add to their number1 and to set      
distinctly before the eyes other stars  
in myriads1 which have never been seen  

before1 and which surpass the old1      
previously known1 stars in number more  
than ten times4  ,again1 it is a most   
beautiful and delightful sight to behold
 the body of the ,moon1 which is distant
 from us nearly sixty semi-diameters#d  
of the ,earth1 as near as if it was at a
 distance of only two of the same       
measures2 so that the diameter of this  
same ,moon appears about thirty times   
larger1 its surface about nine hundred  
times1 and its solid mass nearly #bg1jjj
 times larger than when it is viewed    
only with the naked eye2 and            
consequently any one may know with the  
certainty that is due to the use of our 
senses1 that the ,moon certainly does   
not possess a smooth and polished       
surface1 but one rough and uneven1 and1 
just like the face of the ,earth itself1
 is everywhere full of vast             
protuberances1 deep chasms1 and         
sinuosities4      #d ,galileo says1 8per
 sex denas fere terrestres diametros a  
nobis remotum0 by mistake for           

semi-diametros1 and the same     mistake
 occurs in p4 #aa4  ,then to have got   
rid of disputes about the ,galaxy or    
,milky ,way1 and to have made its nature
 clear to the very senses1 not to say to
 the understanding1 seems by no means a 
matter which ought to be considered of  
slight importance4 ,in addition to this1
 to point out1 as with one's finger1 the
 nature of those stars which every one  
of the astronomers up to this time has  
called nebulous1 and to demonstrate that
 it is very different from what has     
hitherto been believed1 will be         
pleasant1 and very fine4 ,but that which
 will excite the greatest astonishment  
by far1 and which indeed especially     
moved me to call the attention of all   
astronomers and philosophers1 is this1  
namely1 that ,i have discovered four    
planets1 neither known nor observed by  
any one of the astronomers before my    
time1 which have their orbits round a   
certain bright star1 one of those       
previously known1 like ,venus and       

,mercury round the ,sun1 and are        
sometimes in front of it1 sometimes     
behind it1 though they never depart from
 it beyond certain limits4 ,all which   
facts were discovered and observed a few
 days ago by the help of a telescope#e  
devised by me1 through ,god's grace     
first enlightening my mind4      #e ,the
 words used by ,galileo for 8telescope0 
are perspicillum1     specillum         
instrumentum1 organum1 and occhiale     
7,ital474     ,kepler uses also oculare 
tubus1 arundo dioptrica4 ,the word      
8telescopium0 is used by ,gassendi1     
#afdg4  ,perchance other discoveries    
still more excellent will be made from  
time to time by me or by other          
observers1 with the assistance of a     
similar instrument1 so ,i will first    
briefly record its shape and            
preparation1 as well as the occasion of 
its being devised1 and then ,i will give
 an account of the observations made by 
me4  ,sidenote3 ,galileo's account of   
the invention of his telescope4  ,about 

ten months ago a report reached my ears 
that a ,dutchman had constructed a      
telescope1 by the aid of which visible  
objects1 although at a great distance   
from the eye of the observer1 were seen 
distinctly as if near2 and some proofs  
of its most wonderful performances were 
reported1 which some gave credence to1  
but others contradicted4 ,a few days    
after1 ,i received confirmation of the  
report in a letter written from ,paris  
by a noble ,frenchman1 ,jaques          
,badovere1 which finally determined me  
to give myself up first to inquire into 
the principle of the telescope1 and then
 to consider the means by which ,i might
 compass the invention of a similar     
instrument1 which a little while after  
,i succeeded in doing1 through deep     
study of the theory of ,refraction2 and 
,i prepared a tube1 at first of lead1 in
 the ends of which ,i fitted two glass  
lenses1 both plane on one side1 but on  
the other side one spherically convex1  
and the other concave4 ,then bringing my

 eye to the concave lens ,i saw objects 
satisfactorily large and near1 for they 
appeared one-third of the distance off  
and nine times larger than when they are
 seen with the natural eye alone4 ,i    
shortly afterwards constructed another  
telescope with more nicety1 which       
magnified objects more than sixty times4
 ,at length1 by sparing neither labour  
nor expense1 ,i succeeded in            
constructing for myself an instrument so
 superior that objects seen through it  
appear magnified nearly a thousand      
times1 and more than thirty times nearer
 than if viewed by the natural powers of
 sight alone4  ,sidenote3 ,galileo's    
first observations with his telescope4  
,it would be altogether a waste of time 
to enumerate the number and importance  
of the benefits which this instrument   
may be expected to confer1 when used by 
land or sea4 ,but without paying        
attention to its use for terrestrial    
objects1 ,i betook myself to            
observations of the heavenly bodies2 and

 first of all1 ,i viewed the ,moon as   
near as if it was scarcely two          
semi-diameters#f of the ,earth distant4 
,after the ,moon1 ,i frequently observed
 other heavenly bodies1 both fixed stars
 and planets1 with incredible delight2  
and1 when ,i saw their very great       
number1 ,i began to consider about a    
method by which ,i might be able to     
measure their distances apart1 and at   
length ,i found one4 ,and here it is    
fitting that all who intend to turn     
their attention to observations of this 
kind should receive certain cautions4   
,for1 in the first place1 it is         
absolutely necessary for them to prepare
 a most perfect telescope1 one which    
will show very bright objects distinct  
and free from any mistiness1 and will   
magnify them at least #djj times1 for   
then it will show them as if only       
one-twentieth of their distance off4    
,for unless the instrument be of such   
power1 it will be in vain to attempt to 
view all the things which have been seen

 by me in the heavens1 or which will be 
enumerated hereafter4      #f 8,vix per 
duas ,telluris diametros10 by mistake   
for     8semi-diametros40  ,sidenote3   
,method of determining the magnifying   
power of the telescope4  ,but in order  
that any one may be a little more       
certain about the magnifying power of   
his instrument1 he shall fashion two    
circles1 or two square pieces of paper1 
one of which is #djj times greater than 
the other1 but that will be when the    
diameter of the greater is twenty times 
the length of the diameter of the other4
 ,then he shall view from a distance    
simultaneously both surfaces1 fixed on  
the same wall1 the smaller with one eye 
applied to the telescope1 and the larger
 with the other eye unassisted2 for that
 may be done without inconvenience at   
one and the same instant with both eyes 
open4 ,then both figures will appear of 
the same size1 if the instrument        
magnifies objects in the desired        
proportion4  ,sidenote3 ,method of      

measuring small angular distances       
between heavenly bodies by the size of  
the aperture of the telescope4  ,after  
such an instrument has been prepared1   
the method of measuring distances       
remains for inquiry1 and this we shall  
accomplish by the following             
contrivance3--  ,illustration  ,for the 
sake of being more easily understood1 ,i
 will suppose a tube ,a ,b ,c ,d4#g ,let
 ,e be the eye of the observer2 then1   
when there are no lenses in the tube    
rays from the eye to the object ,f ,g   
would be drawn in the straight lines ,e 
,c ,f1 ,e ,d ,g1 but when the lenses    
have been inserted1 let the rays go in  
the bent lines ,e ,c ,h1 ,e ,d ,i1--for 
they are contracted1 and those which    
originally1 when unaffected by the      
lenses1 were directed to the object ,f  
,g1 will include only the part ,h ,i4   
,hence the ratio of the distance ,e ,h  
to the line ,h ,i being known1 we shall 
be able to find1 by means of a table of 
sines1 the magnitude of the angle       

subtended at the eye by the object ,h   
,i1 which we shall find to contain only 
some minutes4 ,but if we fit on the lens
 ,c ,d thin plates of metal1 pierced1   
some with larger1 others with smaller   
apertures1 by putting on over the lens  
sometimes one plate1 sometimes another1 
as may be necessary1 we shall construct 
at our pleasure different subtending    
angles of more or fewer minutes1 by the 
help of which we shall be able to       
measure conveniently the intervals      
between stars separated by an angular   
distance of some minutes1 within an     
error of one or two minutes4 ,but let it
 suffice for the present to have thus   
slightly touched1 and as it were just   
put our lips to these matters1 for on   
some other opportunity ,i will publish  
the theory of this instrument in        
completeness4      #g ,illustration     
,the line ,c ,h in ,galileo's figure    
represents the small pencil of     rays 
from ,h which1 after refraction through 
the telescope1 reach     the eye ,e4    

,the enlarged figure shows that if ,o ,p
 be the radius of     the aperture      
employed1 the point ,h of the object    
would be just     outside the field of  
view4 ,the method1 however1 is at best  
only     a very rough one1 as the       
boundary of the field of view in this   
telescope is unavoidably indistinct4    
,now let me review the observations made
 by me during the two months just past1 
again inviting the attention of all who 
are eager for true philosophy to the    
beginnings which led to the sight of    
most important phenomena4  ,sidenote3   
,the ,moon4 ,ruggedness of its surface4 
,existence of lunar mountains and       
valleys4  ,let me speak first of the    
surface of the ,moon1 which is turned   
towards us4 ,for the sake of being      
understood more easily1 ,i distinguish  
two parts in it1 which ,i call          
respectively the brighter and the       
darker4 ,the brighter part seems to     
surround and pervade the whole          
hemisphere2 but the darker part1 like a 

sort of cloud1 discolours the ,moon's   
surface and makes it appear covered with
 spots4 ,now these spots1 as they are   
somewhat dark and of considerable size1 
are plain to every one1 and every age   
has seen them1 wherefore ,i shall call  
them great or ancient spots1 to         
distinguish them from other spots1      
smaller in size1 but so thickly         
scattered that they sprinkle the whole  
surface of the ,moon1 but especially the
 brighter portion of it4 ,these spots   
have never been observed by any one     
before me2 and from my observations of  
them1 often repeated1 ,i have been led  
to that opinion which ,i have expressed1
 namely1 that ,i feel sure that the     
surface of the ,moon is not perfectly   
smooth1 free from inequalities and      
exactly spherical1 as a large school of 
philosophers considers with regard to   
the ,moon and the other heavenly bodies1
 but that1 on the contrary1 it is full  
of inequalities1 uneven1 full of hollows
 and protuberances1 just like the       

surface of the ,earth itself1 which is  
varied everywhere by lofty mountains and
 deep valleys4  ,sketches by ,galileo to
 shew3--  ,illustration3 the indentation
 of the terminator and illuminated      
summits of mountains in the dark part of
 the moon2  ,illustration3 the shape of 
a lunar mountain and of a walled plain4 
,galileo3 #8,sidereus ,nuncius1' ,venice
 #afaj4  ,the appearances from which we 
may gather these conclusions are of the 
following nature3--,on the fourth or    
fifth day after new-moon1 when the ,moon
 presents itself to us with bright      
horns1 the boundary which divides the   
part in shadow from the enlightened part
 does not extend continuously in an     
ellipse1 as would happen in the case of 
a perfectly spherical body1 but it is   
marked out by an irregular1 uneven1 and 
very wavy line1 as represented in the   
figure given1 for several bright        
excrescences1 as they may be called1    
extend beyond the boundary of light and 
shadow into the dark part1 and on the   

other hand pieces of shadow encroach    
upon the light3--nay1 even a great      
quantity of small blackish spots1       
altogether separated from the dark part1
 sprinkle everywhere almost the whole   
space which is at the time flooded with 
the ,sun's light1 with the exception of 
that part alone which is occupied by the
 great and ancient spots4 ,i have       
noticed that the small spots just       
mentioned have this common              
characteristic always and in every case1
 that they have the dark part towards   
the ,sun's position1 and on the side    
away from the ,sun they have brighter   
boundaries1 as if they were crowned with
 shining summits4 ,now we have an       
appearance quite similar on the ,earth  
about sunrise1 when we behold the       
valleys1 not yet flooded with light1 but
 the mountains surrounding them on the  
side opposite to the ,sun already ablaze
 with the splendour of his beams2 and   
just as the shadows in the hollows of   
the ,earth diminish in size as the ,sun 

rises higher1 so also these spots on the
 ,moon lose their blackness as the      
illuminated part grows larger and       
larger4 ,again1 not only are the        
boundaries of light and shadow in the   
,moon seen to be uneven and sinuous1    
but--and this produces still greater    
astonishment--there appear very many    
bright points within the darkened       
portion of the ,moon1 altogether divided
 and broken off from the illuminated    
tract1 and separated from it by no      
inconsiderable interval1 which1 after a 
little while1 gradually increase in size
 and brightness1 and after an hour or   
two become joined on to the rest of the 
bright portion1 now become somewhat     
larger2 but in the meantime others1 one 
here and another there1 shooting up as  
if growing1 are lighted up within the   
shaded portion1 increase in size1 and at
 last are linked on to the same luminous
 surface1 now still more extended4 ,an  
example of this is given in the same    
figure4 ,now1 is it not the case on the 

,earth before sunrise1 that while the   
level plain is still in shadow1 the     
peaks of the most lofty mountains are   
illuminated by the ,sun's rays8 ,after a
 little while does not the light spread 
further1 while the middle and larger    
parts of those mountains are becoming   
illuminated2 and at length1 when the    
,sun has risen1 do not the illuminated  
parts of the plains and hills join      
together8 ,the grandeur1 however1 of    
such prominences and depressions in the 
,moon seems to surpass both in magnitude
 and extent the ruggedness of the       
,earth's surface1 as ,i shall hereafter 
show4 ,and here ,i cannot refrain from  
mentioning what a remarkable spectacle  
,i observed while the ,moon was rapidly 
approaching her first quarter1 a        
representation of which is given in the 
same illustration1 placed opposite page 
#af4 ,a protuberance of the shadow1 of  
great size1 indented the illuminated    
part in the neighbourhood of the lower  
cusp2 and when ,i had observed this     

indentation longer1 and had seen that it
 was dark throughout1 at length1 after  
about two hours1 a bright peak began to 
arise a little below the middle of the  
depression2 this by degrees increased1  
and presented a triangular shape1 but   
was as yet quite detached and separated 
from the illuminated surface4 ,soon     
around it three other small points began
 to shine1 until1 when the ,moon was    
just about to set1 that triangular      
figure1 having now extended and widened1
 began to be connected with the rest of 
the illuminated part1 and1 still girt   
with the three bright peaks already     
mentioned1 suddenly burst into the      
indentation of shadow like a vast       
promontory of light4  ,at the ends of   
the upper and lower cusps also certain  
bright points1 quite away from the rest 
of the bright part1 began to rise out of
 the shadow1 as is seen depicted in the 
same illustration4  ,sidenote3 ,the     
lunar spots are suggested to be possibly
 seas bordered by ranges of mountains4  

,in both horns also1 but especially in  
the lower one1 there was a great        
quantity of dark spots1 of which those  
which are nearer the boundary of light  
and shadow appear larger and darker1 but
 those which are more remote less dark  
and more indistinct4 ,in all cases1     
however1 just as ,i have mentioned      
before1 the dark portion of the spot    
faces the position of the ,sun's        
illumination1 and a brighter edge       
surrounds the darkened spot on the side 
away from the ,sun1 and towards the     
region of the ,moon in shadow4 ,this    
part of the surface of the ,moon1 where 
it is marked with spots like a peacock's
 tail with its azure eyes1 is rendered  
like those glass vases which1 through   
being plunged while still hot from the  
kiln into cold water1 acquire a crackled
 and wavy surface1 from which           
circumstance they are commonly called   
frosted glasses4#h ,now the great spots 
of the ,moon observed at the same time  
are not seen to be at all similarly     

broken1 or full of depressions and      
prominences1 but rather to be even and  
uniform2 for only here and there some   
spaces1 rather brighter than the rest1  
crop up2 so that if any one wishes to   
revive the old opinion of the           
,pythagoreans1 that the ,moon is another
 ,earth1 so to say1 the brighter portion
 may very fitly represent the surface of
 the land1 and the darker the expanse of
 water4 ,indeed1 ,i have never doubted  
that if the sphere of the ,earth were   
seen from a distance1 when flooded with 
the ,sun's rays1 that part of the       
surface which is land would present     
itself to view as brighter1 and that    
which is water as darker in comparison4 
,moreover1 the great spots in the ,moon 
are seen to be more depressed than the  
brighter tracts2 for in the ,moon1 both 
when crescent and when waning1 on the   
boundary between the light and shadow1  
which projects in some places round the 
great spots1 the adjacent regions are   
always brighter1 as ,i have noticed in  

drawing my illustrations1 and the edges 
of the spots referred to are not only   
more depressed than the brighter parts1 
but are more even1 and are not broken by
 ridges or ruggednesses4 ,but the       
brighter part stands out most near the  
spots1 so that both before the first    
quarter and about the third quarter     
also1 around a certain spot in the upper
 part of the figure1 that is1 occupying 
the northern region of the ,moon1 some  
vast prominences on the upper and lower 
sides of it rise to an enormous         
elevation1 as the illustrations show4   
,this same spot before the third quarter
 is seen to be walled round with        
boundaries of a deeper shade1 which just
 like very lofty mountain summits appear
 darker on the side away from the ,sun1 
and brighter on the side where they face
 the ,sun2 but in the case of the       
cavities the opposite happens1 for the  
part of them away from the ,sun appears 
brilliant1 and that part which lies     
nearer to the ,sun dark and in shadow4  

,after a time1 when the enlightened     
portion of the ,moon's surface has      
diminished in size1 as soon as the whole
 or nearly so of the spot already       
mentioned is covered with shadow1 the   
brighter ridges of the mountains mount  
high above the shade4 ,these two        
appearances are shown in the            
illustrations which are given4      #h  
,specimens of frosted or crackled       
,venetian glass are to be     seen in   
the ,slade ,collection1 ,british        
,museum1 and fully justify              
,galileo's comparison4  ,sidenote3      
,description of a lunar crater1 perhaps 
,tycho4#i      #i ,webb1 ,celestial     
,objects for ,common ,telescopes1 p4    
#ajd1     suggests this identification4 
,there is one other point which ,i must 
on no account forget1 which ,i have     
noticed and rather wondered at4 ,it is  
this3--,the middle of the ,moon1 as it  
seems1 is occupied by a certain cavity  
larger than all the rest1 and in shape  
perfectly round4 ,i have looked at this 

depression near both the first and third
 quarters1 and ,i have represented it as
 well as ,i can in the second           
illustration already given4 ,it produces
 the same appearance as to effects of   
light and shade as a tract like ,bohemia
 would produce on the ,earth1 if it were
 shut in on all sides by very lofty     
mountains arranged on the circumference 
of a perfect circle2 for the tract in   
the ,moon is walled in with peaks of    
such enormous height that the furthest  
side adjacent to the dark portion of the
 ,moon is seen bathed in sunlight before
 the boundary between light and shade   
reaches half-way across the circular    
space4 ,but according to the            
characteristic property of the rest of  
the spots1 the shaded portion of this   
too faces the ,sun1 and the bright part 
is towards the dark side of the ,moon1  
which for the third time ,i advise to be
 carefully noticed as a most solid proof
 of the ruggednesses and unevennesses   
spread over the whole of the bright     

region of the ,moon4 ,of these spots1   
moreover1 the darkest are always those  
which are near to the boundary-line     
between the light and the shadow1 but   
those further off appear both smaller in
 size and less decidedly dark2 so that  
at length1 when the ,moon at opposition 
becomes full1 the darkness of the       
cavities differs from the brightness of 
the prominences with a subdued and very 
slight difference4  ,sidenote3 ,reasons 
for believing that there is a difference
 of constitution in various parts of the
 ,moon's surface4  ,these phenomena     
which we have reviewed are observed in  
the bright tracts of the ,moon4 ,in the 
great spots we do not see such          
differences of depressions and          
prominences as we are compelled to      
recognise in the brighter parts1 owing  
to the change of their shapes under     
different degrees of illumination by the
 ,sun's rays according to the manifold  
variety of the ,sun's position with     
regard to the ,moon4 ,still1 in the     

great spots there do exist some spaces  
rather less dark than the rest1 as ,i   
have noted in the illustrations1 but    
these spaces always have the same       
appearance1 and the depth of their      
shadow is neither intensified nor       
diminished2 they do appear indeed       
sometimes a little more shaded1         
sometimes a little less1 but the change 
of colour is very slight1 according as  
the ,sun's rays fall upon them more or  
less obliquely2 and besides1 they are   
joined to the adjacent parts of the     
spots with a very gradual connection1 so
 that their boundaries mingle and melt  
into the surrounding region4 ,but it is 
quite different with the spots which    
occupy the brighter parts of the ,moon's
 surface1 for1 just as if they were     
precipitous crags with numerous rugged  
and jagged peaks1 they have well-defined
 boundaries through the sharp contrast  
of light and shade4 ,moreover1 inside   
those great spots certain other tracts  
are seen brighter than the surrounding  

region1 and some of them very bright    
indeed1 but the appearance of these1 as 
well as of the darker parts1 is always  
the same2 there is no change of shape or
 brightness or depth of shadow1 so that 
it becomes a matter of certainty and    
beyond doubt that their appearance is   
owing to real dissimilarity of parts1   
and not to unevennesses only in their   
configuration1 changing in different    
ways the shadows of the same parts      
according to the variations of their    
illumination by the ,sun1 which really  
happens in the case of the other smaller
 spots occupying the brighter portion of
 the ,moon1 for day by day they change1 
increase1 decrease1 or disappear1       
inasmuch as they derive their origin    
only from the shadows of prominences4   
,sidenote3 ,explanation of the evenness 
of the illuminated part of the          
circumference of the ,moon's orb by the 
analogy of terrestrial phenomena1 or by 
a possible lunar atmosphere4  ,but here 
,i feel that some people may be troubled

 with grave doubt1 and perhaps seized   
with a difficulty so serious as to      
compel them to feel uncertain about the 
conclusion just explained and supported 
by so many phenomena4 ,for if that part 
of the ,moon's surface which reflects   
the ,sun's rays most brightly is full of
 sinuosities1 protuberances1 and        
cavities innumerable1 why1 when the     
,moon is increasing1 does the outer edge
 which looks toward the west1 when the  
,moon is waning1 the other              
half-circumference towards the east1 and
 at full-moon the whole circle1 appear  
not uneven1 rugged1 and irregular1 but  
perfectly round and circular1 as sharply
 defined as if marked out with a pair of
 compasses1 and without the indentations
 of any protuberances or cavities8 ,and 
most remarkably so1 because the whole   
unbroken edge belongs to that part of   
the ,moon's surface which possesses the 
property of appearing brighter than the 
rest1 which ,i have said to be          
throughout full of protuberances and    

cavities4 ,for not one of the ,great    
,spots extends quite to the             
circumference1 but all of them are seen 
to be together away from the edge4 ,of  
this phenomenon1 which affords a handle 
for such serious doubt1 ,i produce two  
causes1 and so two solutions of the     
difficulty4  ,the first solution which  
,i offer is this3--,if the protuberances
 and cavities in the body of the ,moon  
existed only on the edge of the circle  
that bounds the hemisphere which we see1
 then the ,moon might1 or rather must1  
show itself to us with the appearance of
 a toothed wheel1 being bounded with an 
irregular and uneven circumference2 but 
if1 instead of a single set of          
prominences arranged along the actual   
circumference only1 very many ranges of 
mountains with their cavities and       
ruggednesses are set one behind the     
other along the extreme edge of the     
,moon1 and that too not only in the     
hemisphere which we see1 but also in    
that which is turned away from us1 but  

still near the boundary of the          
hemisphere1 then the eye1 viewing them  
afar off1 will not at all be able to    
detect the differences of prominences   
and cavities1 for the intervals between 
the mountains situated in the same      
circle1 or in the same chain1 are hidden
 by the jutting forward of other        
prominences situated in other ranges1   
and especially if the eye of the        
observer is placed in the same line with
 the tops of the prominences mentioned4 
,so on the ,earth1 the summits of a     
number of mountains close together      
appear situated in one plane1 if the    
spectator is a long way off and standing
 at the same elevation4 ,so when the sea
 is rough1 the tops of the waves seem to
 form one plane1 although between the   
billows there is many a gulf and chasm1 
so deep that not only the hulls1 but    
even the bulwarks1 masts1 and sails of  
stately ships are hidden amongst them4  
,therefore1 as within the ,moon1 as well
 as round her circumference1 there is a 

manifold arrangement of prominences and 
cavities1 and the eye1 regarding them   
from a great distance1 is placed in     
nearly the same plane with their        
summits1 no one need think it strange   
that they present themselves to the     
visual ray which just grazes them as an 
unbroken line quite free from           
unevennesses4 ,to this explanation may  
be added another1 namely1 that there is 
round the body of the ,moon1 just as    
round the ,earth1 an envelope of some   
substance denser than the rest of the   
ether1 which is sufficient to receive   
and reflect the ,sun's rays1 although it
 does not possess so much opaqueness as 
to be able to prevent our seeing through
 it--especially when it is not          
illuminated4 ,that envelope1 when       
illuminated by the ,sun's rays1 renders 
the body of the ,moon apparently larger 
than it really is1 and would be able to 
stop our sight from penetrating to the  
solid body of the ,moon1 if its         
thickness were greater2 now1 it is of   

greater thickness about the             
circumference of the ,moon1 greater1 ,i 
mean1 not in actual thickness1 but with 
reference to our sight-rays1 which cut  
it obliquely2 and so it may stop our    
vision1 especially when it is in a state
 of brightness1 and may conceal the true
 circumference of the ,moon on the side 
towards the ,sun4  ,illustration  ,this 
may be understood more clearly from the 
adjoining figure1 in which the body of  
the ,moon1 ,a ,b ,c1 is surrounded by an
 enveloping atmosphere1 ,d ,e ,g4 ,an   
eye at ,f penetrates to the middle parts
 of the ,moon1 as at ,a1 through a      
thickness1 ,d ,a1 of the atmosphere2 but
 towards the extreme parts a mass of    
atmosphere of greater depth1 ,e ,b1     
shuts out its boundary from our sight4  
,an argument in favour of this is1 that 
the illuminated portion of the ,moon    
appears of larger circumference than the
 rest of the orb which is in shadow4    
,perhaps also some will think that this 
same cause affords a very reasonable    

explanation why the greater spots on the
 ,moon are not seen to reach to the edge
 of the circumference on any side1      
although it might be expected that some 
would be found about the edge as well as
 elsewhere2 and it seems credible that  
there are spots there1 but that they    
cannot be seen because they are hidden  
by a mass of atmosphere too thick and   
too bright for the sight to penetrate4  
,illustration  ,sidenote3 ,calculation  
to show that the height of some lunar   
mountains exceeds four ,italian miles#aj
 7#bb1jjj ,british feet74      #aj ,in  
the list of the heights of lunar        
mountains determined by     ,beer and   
,maedler1 given in their work ,der ,mond
 7,berlin1 #ahcg71     there are six    
which exceed #cjjj toises1 or #ai1jjj   
,british feet4  ,i think that it has    
been sufficiently made clear1 from the  
explanation of phenomena which have been
 given1 that the brighter part of the   
,moon's surface is dotted everywhere    
with protuberances and cavities2 it only

 remains for me to speak about their    
size1 and to show that the ruggednesses 
of the ,earth's surface are far smaller 
than those of the ,moon's2 smaller1 ,i  
mean1 absolutely1 so to say1 and not    
only smaller in proportion to the size  
of the orbs on which they are4 ,and this
 is plainly shown thus3--,as ,i often   
observed in various positions of the    
,moon with reference to the ,sun1 that  
some summits within the portion of the  
,moon in shadow appeared illumined1     
although at some distance from the      
boundary of the light 7the terminator71 
by comparing their distance with the    
complete diameter of the ,moon1 ,i      
learnt that it sometimes exceeded the   
one-twentieth 7#a_/bjth7 part of the    
diameter4 ,suppose the distance to be   
exactly #a_/bjth part of the diameter1  
and let the diagram represent the       
,moon's orb1 of which ,c ,a ,f is a     
great circle1 ,e its centre1 and ,c ,f a
 diameter1 which consequently bears to  
the diameter of the ,earth the ratio    

#b3g2 and since the diameter of the     
,earth1 according to the most exact     
observations1 contains #gjjj ,italian   
miles1 ,c ,f will be #bjjj1 and ,c ,e   
#ajjj1 and the #a_/bjth part of the     
whole1 ,c ,f1 #ajj miles4 ,also let ,c  
,f be a diameter of the great circle    
which divides the bright part of the    
,moon from the dark part 7for1 owing to 
the very great distance of the ,sun from
 the ,moon this circle does not differ  
sensibly from a great one71 and let the 
distance of ,a from the point ,c be     
#a_/bjth part of that diameter2 let the 
radius ,e ,a be drawn1 and let it be    
produced to cut the tangent line ,g ,c  
,d1 which represents the ray that       
illumines the summit1 in the point ,d4  
,then the arc ,c ,a or the straight line
 ,c ,d will be #ajj of such units1 as ,c
 ,e contains #ajjj4 ,the sum of the     
squares of ,d ,c1 ,c ,e is therefore    
#a1jaj1jjj1 and the square of ,d ,e is  
equal to this2 therefore the whole ,e ,d
 will be more than #ajjd2 and ,a ,d will

 be more than #d of such units1 as ,c ,e
 contained #ajjj4 ,therefore the height 
of ,a ,d in the ,moon1 which represents 
a summit reaching up to the ,sun's ray1 
,g ,c ,d1 and separated from the        
extremity ,c by the distance ,c ,d1 is  
more than #d ,italian miles2 but in the 
,earth there are no mountains which     
reach to the perpendicular height even  
of one mile4 ,we are therefore left to  
conclude that it is clear that the      
prominences of the ,moon are loftier    
than those of the ,earth4  ,sidenote3   
,the faint illumination of the ,moon's  
disc about new-moon explained to be due 
to earth-light4  ,i wish in this place  
to assign the cause of another lunar    
phenomenon well worthy of notice1 and   
although this phenomenon was observed by
 me not lately1 but many years ago1 and 
has been pointed out to some of my      
intimate friends and pupils1 explained1 
and assigned to its true cause1 yet as  
the observation of it is rendered easier
 and more vivid by the help of a        

telescope1 ,i have considered that it   
would not be unsuitably introduced in   
this place1 but ,i wish to introduce it 
chiefly in order that the connection and
 resemblance between the ,moon and the  
,earth may appear more plainly4  ,when  
the ,moon1 both before and after        
conjunction1 is found not far from the  
,sun1 not only does its orb show itself 
to our sight on the side where it is    
furnished with shining horns1 but a     
slight and faint circumference is also  
seen to mark out the circle of the dark 
part1 that part1 namely1 which is turned
 away from the ,sun1 and to separate it 
from the darker background of the sky4  
,but if we examine the matter more      
closely1 we shall see that not only is  
the extreme edge of the part in shadow  
shining with a faint brightness1 but    
that the entire face of the ,moon1 that 
side1 that is1 which does not feel the  
,sun's glare1 is illuminated with a pale
 light of considerable brightness4 ,at  
the first glance only a fine            

circumference appears shining1 on       
account of the darker part of the sky   
adjacent to it2 whereas1 on the         
contrary1 the rest of the surface       
appears dark1 on account of the         
contiguity of the shining horns1 which  
destroys the clearness of our sight4    
,but if any one chooses such a position 
for himself1 that by the interposition  
of a roof1 or a chimney1 or some other  
object between his sight and the ,moon1 
but at a considerable distance from his 
eye1 the shining horns are hidden1 and  
the rest of the ,moon's orb is left     
exposed to his view1 then he will find  
that this tract of the ,moon also1      
although deprived of sunlight1 gleams   
with considerable light1 and            
particularly so if the gloom of the     
night has already deepened through the  
absence of the ,sun2 for with a darker  
background the same light appears       
brighter4 ,moreover1 it is found that   
this secondary brightness of the ,moon1 
as ,i may call it1 is greater in        

proportion as the ,moon is less distant 
from the ,sun2 for it abates more and   
more in proportion to the ,moon's       
distance from that body1 so much so that
 after the first quarter1 and before the
 end of the second1 it is found to be   
weak and very faint1 although it be     
observed in a darker sky2 whereas1 at an
 angular distance of #fj or less1 even  
during twilight1 it is wonderfully      
bright1 so bright indeed that1 with the 
help of a good telescope1 the great     
spots may be distinguished in it4  ,this
 strange brightness has afforded no     
small perplexity to philosophical minds2
 and some have published one thing1 some
 another1 as the cause to be alleged for
 it4 ,some have said that it is the     
inherent and natural brightness of the  
,moon2 some that it is imparted to that 
body by the planet ,venus2 or1 as others
 maintain1 by all the stars2 while some 
have said that it comes from the ,sun1  
whose rays1 they say1 find a way through
 the solid mass of the ,moon4 ,but      

statements of this kind are disproved   
without much difficulty1 and            
convincingly demonstrated to be false4  
,for if this kind of light were the     
,moon's own1 or were contributed by the 
stars1 the ,moon would retain it1       
particularly in eclipses1 and would show
 it then1 when left in an unusually dark
 sky1 but this is contrary to           
experience4 ,for the brightness which is
 seen on the ,moon in eclipses is far   
less intense1 being somewhat reddish1   
and almost copper-coloured1 whereas this
 is brighter and whiter2 besides1 the   
brightness seen during an eclipse is    
changeable and shifting1 for it wanders 
over the face of the ,moon1 so that that
 part which is near the circumference of
 the circle of shadow thrown by the     
,earth is bright1 but the rest of the   
,moon is always seen to be dark4 ,from  
which circumstance we understand without
 hesitation that this brightness is due 
to the proximity of the ,sun's rays     
coming into contact with some denser    

region which surrounds the ,moon as an  
envelope2 owing to which contact a sort 
of dawn-light is diffused over the      
neighbouring regions of the ,moon1 just 
as the twilight spreads in the morning  
and evening on the ,earth3#aa but ,i    
will treat more fully of this matter in 
my book upon the ,system of the         
,universe4#ab      #aa ,the illumination
 of the ,moon in eclipses1 noticed by   
,galileo1     is now referred to the    
refraction of the sunlight by the       
earth's     atmosphere1 and the reddish 
colour of the light is explained by     
,herschel 7,outlines of ,astronomy1 ch4 
vii47 to be due to the     absorption of
 the violet and blue rays by the aqueous
 vapour of the     ,earth's atmosphere4 
,the idea of a sensible lunar atmosphere
 is not     in accordance with the      
observed phenomena of the occultations  
of     stars4      #ab ,galileo's       
,systema ,mundi4 ,owing to the violent  
opposition     provoked by the          
discussion of the discoveries of        

,galileo1 and     their bearing on the  
,copernican system of astronomy1        
,galileo seems     to have found it     
necessary to delay the publication of   
this work     until #afcb1 when1        
believing himself safe under the        
friendship and     patronage of ,pope   
,urban ,,viii4 and others in power at   
,rome1 he     at length published it4   
,urban1 however1 now turned against him1
     denounced the book and its author1 
and summoned him to ,rome1 where     the
 well-known incidents of his trial and  
condemnation took place4  ,again1 to    
assert that this sort of light is       
imparted to the ,moon by the planet     
,venus is so childish as to be          
undeserving of an answer2 for who is so 
ignorant as not to understand that at   
conjunction and within an angular       
distance of #fj it is quite impossible  
for the part of the ,moon turned away   
from the ,sun to be seen by the planet  
,venus8  ,but that this light is derived
 from the ,sun penetrating with its     

light the solid mass of the ,moon1 and  
rendering it luminous1 is equally       
untenable4 ,for then this light would   
never lessen1 since the hemisphere of   
the ,moon is always illumined by the    
,sun1 except at the moment of a lunar   
eclipse1 yet really it quickly decreases
 while the ,moon is drawing near to the 
end of her first quarter1 and when she  
has passed her first quarter it becomes 
quite dull4 ,since1 therefore1 this kind
 of secondary brightness is not inherent
 and the ,moon's own1 nor borrowed from 
any of the stars1 nor from the ,sun1 and
 since there now remains in the whole   
universe no other body whatever except  
the ,earth1 what1 pray1 must we         
conclude8 ,what must we assert8 ,shall  
we assert that the body of the ,moon1 or
 some other dark and sunless orb1       
receives light from the ,earth8 ,why    
should it not be the ,moon8 ,and most   
certainly it is4 ,the ,earth1 with fair 
and grateful exchange1 pays back to the 
,moon an illumination like that which it

 receives from the ,moon nearly the     
whole time during the darkest gloom of  
night4 ,let me explain the matter more  
clearly4 ,at conjunction1 when the ,moon
 occupies a position between the ,sun   
and the ,earth1 the ,moon is illuminated
 by the ,sun's rays on her half towards 
the ,sun which is turned away from the  
,earth1 and the other half1 with which  
she regards the ,earth1 is covered with 
darkness1 and so in no degree illumines 
the ,earth's surface4 ,when the ,moon   
has slightly separated from the ,sun1   
straightway she is partly illumined on  
the half directed towards us2 she turns 
towards us a slender silvery crescent1  
and slightly illumines the ,earth2 the  
,sun's illumination increases upon the  
,moon as she approaches her first       
quarter1 and the reflexion of that light
 increases on the ,earth2 the brightness
 in the ,moon next extends beyond the   
semicircle1 and our nights grow         
brighter2 at length the entire face of  
the ,moon looking towards the ,earth is 

irradiated with the most intense        
brightness by the ,sun1 which happens   
when the ,sun and ,moon are on opposite 
sides of the ,earth2 then far and wide  
the surface of the ,earth shines with   
the flood of moonlight2 after this the  
,moon1 now waning1 sends out less       
powerful beams1 and the ,earth is       
illumined less powerfully2 at length the
 ,moon draws near her first position of 
conjunction with the ,sun1 and forthwith
 black night invades the ,earth4 ,in    
such a cycle the moonlight gives us each
 month alternations of brighter and     
fainter illumination4 ,but the benefit  
of her light to the ,earth is balanced  
and repaid by the benefit of the light  
of the ,earth to her2 for while the     
,moon is found near the ,sun about the  
time of conjunction1 she has in front of
 her the entire surface of that         
hemisphere of the ,earth which is       
exposed to the ,sun1 and vividly        
illumined with his beams1 and so        
receives light reflected from the       

,earth4 ,owing to such reflexion1 the   
hemisphere of the ,moon nearer to us1   
though deprived of sunlight1 appears of 
considerable brightness4 ,again1 when   
removed from the ,sun through a         
quadrant1 the ,moon sees only one-half  
of the ,earth's hemisphere illuminated1 
namely the western half1 for the other1 
the eastern1 is covered with the shades 
of night2 the ,moon is1 therefore1 less 
brightly enlightened by the ,earth1 and 
accordingly that secondary light appears
 fainter to us4 ,but if you imagine the 
,moon to be set on the opposite side of 
the ,earth to the ,sun1 she will see the
 hemisphere of the ,earth1 now between  
the ,moon and the ,sun1 quite dark1 and 
steeped in the gloom of night2 if1      
therefore1 an eclipse should accompany  
such a position of the ,moon1 she will  
receive no light at all1 being deprived 
of the illumination of the ,sun and     
,earth together4 ,in any other position1
 with regard to the ,earth and the ,sun1
 the ,moon receives more or less light  

by reflexion from the ,earth1 according 
as she sees a greater or smaller portion
 of the hemisphere of the ,earth        
illuminated by the ,sun2 for such a law 
is observed between these two orbs1 that
 at whatever times the ,earth is most   
brightly enlightened by the ,moon1 at   
those times1 on the contrary1 the ,moon 
is least enlightened by the ,earth2 and 
contrariwise4 ,let these few words on   
this subject suffice in this place2 for 
,i will consider it more fully in my    
,system of the ,universe1 where1 by very
 many arguments and experimental proofs1
 there is shown to be a very strong     
reflexion of the ,sun's light from the  
,earth1 for the benefit of those who    
urge that the ,earth must be separated  
from the starry host1 chiefly for the   
reason that it has neither motion nor   
light1 for ,i will prove that the ,earth
 has motion1 and surpasses the ,moon in 
brightness1 and is not the place where  
the dull refuse of the universe has     
settled down2 and ,i will support my    

demonstration by a thousand arguments   
taken from natural phenomena4           
,sidenote3 ,stars4 ,their appearance in 
the telescope4  ,hitherto ,i have spoken
 of the observations which ,i have made 
concerning the ,moon's body2 now ,i will
 briefly announce the phenomena which   
have been1 as yet1 seen by me with      
reference to the ,fixed ,stars4 ,and    
first of all the following fact is      
worthy of consideration3--,the stars1   
fixed as well as erratic1 when seen with
 a telescope1 by no means appear to be  
increased in magnitude in the same      
proportion as other objects1 and the    
,moon herself1 gain increase of size2   
but in the case of the stars such       
increase appears much less1 so that you 
may consider that a telescope1 which    
7for the sake of illustration7 is       
powerful enough to magnify other objects
 a hundred times1 will scarcely render  
the stars magnified four or five times4 
,but the reason of this is as           
follows3--,when stars are viewed with   

our natural eyesight they do not present
 themselves to us of their bare1 real   
size1 but beaming with a certain        
vividness1 and fringed with sparkling   
rays1 especially when the night is far  
advanced2 and from this circumstance    
they appear much larger than they would 
if they were stripped of those          
adventitious fringes1 for the angle     
which they subtend at the eye is        
determined not by the primary disc of   
the star1 but by the brightness which so
 widely surrounds it4 ,perhaps you will 
understand this most clearly from the   
well-known circumstance that when stars 
rise just at sunset1 in the beginning of
 twilight1 they appear very small1      
although they may be stars of the first 
magnitude2 and even the planet ,venus   
itself1 on any occasion when it may     
present itself to view in broad         
daylight1 is so small to see that it    
scarcely seems to equal a star of the   
last magnitude4 ,it is different in the 
case of other objects1 and even of the  

,moon1 which1 whether viewed in the     
light of midday or in the depth of      
night1 always appears of the same size4 
,we conclude therefore that the stars   
are seen at midnight in uncurtailed     
glory1 but their fringes are of such a  
nature that the daylight can cut them   
off1 and not only daylight1 but any     
slight cloud which may be interposed    
between a star and the eye of the       
observer4 ,a dark veil or coloured glass
 has the same effect1 for1 upon placing 
them before the eye between it and the  
stars1 all the blaze that surrounds them
 leaves them at once4 ,a telescope also 
accomplishes the same result1 for it    
removes from the stars their            
adventitious and accidental splendours  
before it enlarges their true discs 7if 
indeed they are of that shape71 and so  
they seem less magnified than other     
objects1 for a star of the fifth or     
sixth magnitude seen through a telescope
 is shown as of the first magnitude     
only4  ,the difference between the      

appearance of the planets and the fixed 
stars seems also deserving of notice4   
,the planets present their discs        
perfectly round1 just as if described   
with a pair of compasses1 and appear as 
so many little moons1 completely        
illuminated and of a globular shape2 but
 the fixed stars do not look to the     
naked eye bounded by a circular         
circumference1 but rather like blazes of
 light1 shooting out beams on all sides 
and very sparkling1 and with a telescope
 they appear of the same shape as when  
they are viewed by simply looking at    
them1 but so much larger that a star of 
the fifth or sixth magnitude seems to   
equal ,sirius1 the largest of all the   
fixed stars4#ac      #ac ,the immense   
distance of stars makes it impossible   
for them to     be magnified by any     
telescope1 however powerful2 the        
apparent or     spurious disc is an     
optical effect1 which depends on the    
telescope     used1 and is smallest with
 the largest aperture4  ,illustration3  

,orion's ,belt and ,sword2 #hc ,stars   
,illustration3 ,pleiades2 #cf ,stars    
,galileo3 8,sidereus ,nuncius40         
,sidenote3 ,telescopic ,stars3 their    
infinite multitude4 ,as examples1       
,orion's ,belt and ,sword and the       
,pleiades are described as seen by      
,galileo4  ,but beyond the stars of the 
sixth magnitude you will behold through 
the telescope a host of other stars1    
which escape the unassisted sight1 so   
numerous as to be almost beyond belief1 
for you may see more than six other     
differences of magnitude1 and the       
largest of these1 which ,i may call     
stars of the seventh magnitude1 or of   
the first magnitude of invisible stars1 
appear with the aid of the telescope    
larger and brighter than stars of the   
second magnitude seen with the          
unassisted sight4 ,but in order that you
 may see one or two proofs of the       
inconceivable manner in which they are  
crowded together1 ,i have determined to 
make out a case against two             

star-clusters1 that from them as a      
specimen you may decide about the rest4 
,as my first example ,i had determined  
to depict the entire constellation of   
,orion1 but ,i was overwhelmed by the   
vast quantity of stars and by want of   
time1 and so ,i have deferred attempting
 this to another occasion1 for there are
 adjacent to1 or scattered among1 the   
old stars more than five hundred new    
stars within the limits of one or two   
degrees4 ,for this reason ,i have       
selected the three stars in ,orion's    
,belt and the six in his ,sword1 which  
have been long well-known groups1 and ,i
 have added eighty other stars recently 
discovered in their vicinity1 and ,i    
have preserved as exactly as possible   
the intervals between them4 ,the        
well-known or old stars1 for the sake of
 distinction1 ,i have depicted of larger
 size1 and ,i have outlined them with a 
double line2 the others1 invisible to   
the naked eye1 ,i have marked smaller   
and with one line only4 ,i have also    

preserved the differences of magnitude  
as much as ,i could4  ,as a second      
example ,i have depicted the six stars  
of the constellation ,taurus1 called the
 ,pleiades 7,i say six intentionally1   
since the seventh is scarcely ever      
visible71 a group of stars which is     
enclosed in the heavens within very     
narrow precincts4 ,near these there lie 
more than forty others invisible to the 
naked eye1 no one of which is much more 
than half a degree off any of the       
aforesaid six2 of these ,i have noticed 
only thirty-six in my diagram4 ,i have  
preserved their intervals1 magnitudes1  
and the distinction between the old and 
the new stars1 just as in the case of   
the constellation ,orion4  ,sidenote3   
,the ,milky ,way consists entirely of   
stars in countless numbers and of       
various magnitudes4  ,the next object   
which ,i have observed is the essence or
 substance of the ,milky ,way4 ,by the  
aid of a telescope any one may behold   
this in a manner which so distinctly    

appeals to the senses that all the      
disputes which have tormented           
philosophers through so many ages are   
exploded at once by the irrefragable    
evidence of our eyes1 and we are freed  
from wordy disputes upon this subject1  
for the ,galaxy is nothing else but a   
mass of innumerable stars planted       
together in clusters4 ,upon whatever    
part of it you direct the telescope     
straightway a vast crowd of stars       
presents itself to view2 many of them   
are tolerably large and extremely       
bright1 but the number of small ones is 
quite beyond determination4             
,illustration3 ,star-cluster in ,orion's
 ,head  ,illustration3 ,star-cluster of 
,praesepe in ,cancer  ,galileo3         
8,sidereus ,nuncius10 ,venice1 #afaj4   
,sidenote3 ,nebul resolved into clusters
 of stars3 as examples1 the nebul in    
,orion's ,head and ,prsepe4  ,and       
whereas that milky brightness1 like the 
brightness of a white cloud1 is not only
 to be seen in the ,milky ,way1 but     

several spots of a similar colour shine 
faintly here and there in the heavens1  
if you turn the telescope upon any of   
them you will find a cluster of stars   
packed close together4 ,further--and you
 will be more surprised at this1--the   
stars which have been called by every   
one of the astronomers up to this day   
nebulous1 are groups of small stars set 
thick together in a wonderful way1 and  
although each one of them on account of 
its smallness1 or its immense distance  
from us1 escapes our sight1 from the    
commingling of their rays there arises  
that brightness which has hitherto been 
believed to be the denser part of the   
heavens1 able to reflect the rays of the
 stars or the ,sun4  ,i have observed   
some of these1 and ,i wish to subjoin   
the star-clusters of two of these nebul4
 ,first1 you have a diagram of the      
nebula called that of ,orion's ,head1 in
 which ,i have counted twenty-one stars4
  ,the second cluster contains the      
nebula called ,prsepe1 which is not one 

star only1 but a mass of more than forty
 small stars4 ,i have noticed thirty-six
 stars1 besides the ,aselli1 arranged in
 the order of the accompanying diagram4 
,sidenote3 ,discovery of ,jupiter's     
satellites1 ,jan4 #g1 #afaj3 record of  
,galileo's observations during two      
months4  ,i have now finished my brief  
account of the observations which ,i    
have thus far made with regard to the   
,moon1 the ,fixed ,stars1 and the       
,galaxy4 ,there remains the matter1     
which seems to me to deserve to be      
considered the most important in this   
work1 namely1 that ,i should disclose   
and publish to the world the occasion of
 discovering and observing four         
,,planets1 never seen from the very     
beginning of the world up to our own    
times1 their positions1 and the         
observations made during the last two   
months about their movements and their  
changes of magnitude2 and ,i summon all 
astronomers to apply themselves to      
examine and determine their periodic    

times1 which it has not been permitted  
me to achieve up to this day1 owing to  
the restriction of my time4 ,i give them
 warning however again1 so that they may
 not approach such an inquiry to no     
purpose1 that they will want a very     
accurate telescope1 and such as ,i have 
described in the beginning of this      
account4  ,on the #gth day of ,january  
in the present year1 #afaj1 in the      
first#ad hour of the following night1   
when ,i was viewing the constellations  
of the heavens through a telescope1 the 
planet ,jupiter presented itself to my  
view1 and as ,i had prepared for myself 
a very excellent instrument1 ,i noticed 
a circumstance which ,i had never been  
able to notice before1 owing to want of 
power in my other telescope1 namely1    
that three little stars1 small but very 
bright1 were near the planet2 and       
although ,i believed them to belong to  
the number of the fixed stars1 yet they 
made me somewhat wonder1 because they   
seemed to be arranged exactly in a      

straight line1 parallel to the          
ecliptic1#ae and to be brighter than the
 rest of the stars1 equal to them in    
magnitude4 ,the position of them with   
reference to one another and to ,jupiter
 was as follows 7,fig4 #a74      #ad    
,the times of ,galileo's observations   
are to be understood as     reckoned    
from sunset4      #ae ,the satellites of
 ,jupiter revolve in planes very nearly1
     although not exactly1 coincident   
with that of the equator of the         
planet1 which is inclined #c #e #cj to  
the orbit of the planet1     and the    
plane of the orbit is inclined #a #ah   
#ea to the ecliptic4  ,on the east side 
there were two stars1 and a single one  
towards the west4 ,the star which was   
furthest towards the east1 and the      
western star1 appeared rather larger    
than the third4  ,i scarcely troubled at
 all about the distance between them and
 ,jupiter1 for1 as ,i have already said1
 at first ,i believed them to be fixed  
stars2 but when on ,january #hth1 led by

 some fatality1 ,i turned again to look 
at the same part of the heavens1 ,i     
found a very different state of things1 
for there were three little stars all   
west of ,jupiter1 and nearer together   
than on the previous night1 and they    
were separated from one another by equal
 intervals1 as the accompanying         
illustration 7,fig4 #b7 shows4  ,at this
 point1 although ,i had not turned my   
thoughts at all upon the approximation  
of the stars to one another1 yet my     
surprise began to be excited1 how       
,jupiter could one day be found to the  
east of all the aforesaid fixed stars   
when the day before it had been west of 
two of them2 and forthwith ,i became    
afraid lest the planet might have moved 
differently from the calculation of     
astronomers1 and so had passed those    
stars by its own proper motion4 ,i      
therefore waited for the next night with
 the most intense longing1 but ,i was   
disappointed of my hope1 for the sky was
 covered with clouds in every direction4

  ,but on ,january #ajth the stars      
appeared in the following position with 
regard to ,jupiter2 there were two only1
 and both on the east side of ,jupiter1 
the third1 as ,i thought1 being hidden  
by the planet 7,fig4 #c74 ,they were    
situated just as before1 exactly in the 
same straight line with ,jupiter1 and   
along the ,zodiac4  ,when ,i had seen   
these phenomena1 as ,i knew that        
corresponding changes of position could 
not by any means belong to ,jupiter1 and
 as1 moreover1 ,i perceived that the    
stars which ,i saw had been always the  
same1 for there were no others either in
 front or behind1 within a great        
distance1 along the ,zodiac1--at length1
 changing from doubt into surprise1 ,i  
discovered that the interchange of      
position which ,i saw belonged not to   
,jupiter1 but to the stars to which my  
attention had been drawn1 and ,i thought
 therefore that they ought to be        
observed henceforward with more         
attention and precision4  ,accordingly1 

on ,january #aath ,i saw an arrangement 
of the following kind 7,fig4 #d71       
namely1 only two stars to the east of   
,jupiter1 the nearer of which was       
distant from ,jupiter three times as far
 as from the star further to the east2  
and the star furthest to the east was   
nearly twice as large as the other one2 
whereas on the previous night they had  
appeared nearly of equal magnitude4 ,i  
therefore concluded1 and decided        
unhesitatingly1 that there are three    
stars in the heavens moving about       
,jupiter1 as ,venus and ,mercury round  
the ,sun2 which at length was           
established as clear as daylight by     
numerous other subsequent observations4 
,these observations also established    
that there are not only three1 but four1
 erratic sidereal bodies performing     
their revolutions round ,jupiter1       
observations of whose changes of        
position made with more exactness on    
succeeding nights the following account 
will supply4 ,i have measured also the  

intervals between them with the         
telescope in the manner already         
explained4 ,besides this1 ,i have given 
the times of observation1 especially    
when several were made in the same      
night1 for the revolutions of these     
planets are so swift that an observer   
may generally get differences of        
position every hour4  ,jan4 #ab4--;,at  
the first hour of the next night ,i saw 
these heavenly bodies arranged in this  
manner 7,fig4 #e74 ,the satellite#af    
furthest to the east was greater than   
the satellite furthest to the west2 but 
both were very conspicuous and bright2  
the distance of each one from ,jupiter  
was two minutes4 ,a third satellite1    
certainly not in view before1 began to  
appear at the third hour2 it nearly     
touched ,jupiter on the east side1 and  
was exceedingly small4 ,they were all   
arranged in the same straight line1     
along the ecliptic4      #af ,galileo   
continues to call these bodies stars1   
perhaps     meaning 8,medicean stars10  

throughout the description of their     
configurations1 but as he had now       
detected their nature1 it is more       
convenient to call them satellites1 the 
term introduced by ,kepler4  ,jan4      
#ac4--;,for the first time four         
satellites were in view in the following
 position with regard to ,jupiter 7,fig4
 #f74  ,there were three to the west1   
and one to the east2 they made a        
straight line nearly1 but the middle    
satellite of those to the west deviated 
a little from the straight line towards 
the north4 ,the satellite furthest to   
the east was at a distance of #b from   
,jupiter2 there were intervals of #a    
only between ,jupiter and the nearest   
satellite1 and between the satellites   
themselves1 west of ,jupiter4 ,all the  
satellites appeared of the same size1   
and though small they were very         
brilliant1 and far outshone the fixed   
stars of the same magnitude4  ,jan4     
#ad4--,the weather was cloudy4  ,jan4   
#ae4--;,at the third hour of the night  

the four satellites were in the state   
depicted in the next diagram 7,fig4 #g7 
with reference to ,jupiter4  ,all were  
to the west1 and arranged nearly in the 
same straight line2 but the satellite   
which counted third from ,jupiter was   
raised a little to the north4 ,the      
nearest to ,jupiter was the smallest of 
all2 the rest appeared larger and in    
order of magnitude2 the intervals       
between ,jupiter and the three nearest  
satellites were all equal1 and were of  
the magnitude of #b each2 but the       
satellite furthest to the west was      
distant #d from the satellite nearest to
 it4 ,they were very brilliant1 and not 
at all twinkling1 as they have always   
appeared both before and since4 ,but at 
the seventh hour there were only three  
satellites1 presenting with ,jupiter an 
appearance of the following kind 7,fig4 
#h74 ,they were1 that is to say1 in the 
same straight line to a hair2 the       
nearest to ,jupiter was very small1 and 
distant from the planet #c2 the distance

 of the second from this one was #a2 and
 of the third from the second #d #cj4   
,but after another hour the two middle  
satellites were still nearer1 for they  
were only #cj1 or less1 apart4  ,jan4   
#af4--;,at the first hour of the night  
,i saw three satellites arranged in this
 order 7,fig4 #i74 ,jupiter was between 
two of them1 which were at a distance of
 #j #dj from the planet on either side1 
and the third was west of ,jupiter at a 
distance of #h4 ,the satellites near to 
,jupiter appeared brighter than the     
satellite further off1 but not larger4  
,jan4 #ag1 after sunset #j hours #cj    
minutes1 the configuration was of this  
kind 7,fig4 #aj74 ,there was one        
satellite only to the east1 at a        
distance of #c from ,jupiter2 to the    
west likewise there was only one        
satellite1 distant #aa from ,jupiter4   
,the satellite on the east appeared     
twice as large as the satellite to the  
west2 and there were no more than these 
two4 ,but four hours after1 that is1    

nearly at the fifth hour1 a third       
satellite began to emerge on the east   
side1 which1 before its appearance1 as  
,i think1 had been joined with the      
former of the two other satellites1 and 
the position was of this kind 7,fig4    
#aa74 ,the middle satellite was very    
near indeed to the satellite on the     
east1 and was only #bj from it2 and was 
a little towards the south of the       
straight line drawn through the two     
extreme satellites and ,jupiter4  ,jan4 
#ah1 at #j h4 #bj m4 after sunset1 the  
appearance was such as this 7,fig4 #ab74
 ,the satellite to the east was larger  
than the western one1 and was at a      
distance from ,jupiter of #h1 the       
western one being at a distance of #aj4 
,jan4 #ai4--;,at the second hour of the 
night the relative position of the      
satellites was such as this 7,fig4 #ac72
 that is1 there were three satellites   
exactly in a straight line with         
,jupiter1 one to the east1 at a distance
 of #f from ,jupiter2 between ,jupiter  

and the first satellite to the west in  
order1 there was an interval of #e2 this
 satellite was #d off the other one more
 to the west4 ,at that time ,i was      
doubtful whether or no there was a      
satellite between the satellite to the  
east and ,jupiter1 but so very close to 
,jupiter as almost to touch the planet2 
but at the fifth hour ,i saw this       
satellite distinctly1 by that time      
occupying exactly the middle position   
between ,jupiter and the eastern        
satellite1 so that the configuration was
 thus 7,fig4 #ad74 ,moreover1 the       
satellite which had just come into view 
was very small2 yet at the sixth hour it
 was nearly as large as the rest4  ,jan4
 #bj3 #a h4 #ae m4--,a similar          
arrangement was seen 7,fig4 #ae74 ,there
 were three satellites1 so small as     
scarcely to be distinguishable2 their   
distances from ,jupiter1 and from one   
another1 were not more than #a4 ,i was  
doubtful whether on the western side    
there were two satellites or three4     

,about the sixth hour they were grouped 
in this way 7,fig4 #af74 ,the eastern   
satellite was twice as far away from    
,jupiter as before1 that is #b2 on the  
western side1 the satellite in the      
middle was distant from ,jupiter #j #dj1
 and from the satellite still further to
 the west #j #bj2 at length1 at the     
seventh hour1 three satellites were seen
 on the western side 7,fig4 #ag74 ,the  
satellite nearest to ,jupiter was       
distant from the planet #j #bj2 between 
this one and the satellite furthest to  
the west there was an interval of #dj1  
but between these another satellite was 
in view slightly southward of them1 and 
not more than #aj off the most westerly 
satellite4  ,jan4 #ba3 #j h4 #cj        
m4--,there were three satellites on the 
east side2 the satellites and ,jupiter  
were at equal distances apart 7,fig4    
#ah74 ,the intervals were by estimation 
#ej each4 ,there was also one satellite 
on the west1 distant #d from ,jupiter4  
,the satellite on the east side nearest 

to ,jupiter was the least of all4  ,jan4
 #bb3 #b h4--,the grouping of the       
satellites was similar 7,fig4 #ai74     
,there was an interval of #e from the   
satellite on the east to ,jupiter2 from 
,jupiter to the satellite furthest to   
the west #g4 ,the two interior          
satellites on the western side were #j  
#dj apart1 and the satellite nearer to  
,jupiter was #a from the planet4 ,the   
inner satellites were smaller than the  
outer ones1 but they were situated all  
in the same straight line1 along the    
ecliptic1 except that the middle of the 
three western satellites was slightly to
 the south of it1 but at the sixth hour 
of the night they appeared in this      
position 7,fig4 #bj74 ,the satellite on 
the east was very small1 at a distance  
from ,jupiter of #e as before2 but the  
three satellites on the west were       
separated by equal distances from       
,jupiter and from each other2 and the   
intervals were nearly #a #bj each4 ,the 
satellite nearest ,jupiter appeared     

smaller than the other two on the same  
side1 but they all appeared arranged    
exactly in the same straight line4      
,jan4 #bc1 at #j h4 #dj m4 after sunset1
 the grouping of the satellites was     
nearly after this fashion 7,fig4 #ba74  
,there were three satellites with       
,jupiter in a straight line along the   
ecliptic1 as they always have been2 two 
were on the east of the planet1 one on  
the west2 the satellite furthest to the 
east was #g from the next one1 and this 
satellite #b #dj from ,jupiter2 ,jupiter
 was #c #bj from the satellite on the   
west2 and they were all of nearly the   
same size4 ,but at the fifth hour the   
two satellites which had been previously
 near ,jupiter were no longer visible1  
being1 as ,i suppose1 hidden behind     
,jupiter1 and the appearance presented  
was such as this 7,fig4 #bb74  ,jan4    
#bd4--,three satellites1 all on the east
 side1 were visible1 and nearly1 but not
 quite1 in the same straight line with  
,jupiter1 for the satellite in the      

middle was slightly to the south of it  
7,fig4 #bc74 ,the satellite nearest to  
,jupiter was #b distant from the planet2
 the next in order #j #cj from this     
satellite1 and the third was #i further 
off still2 they were all very bright4   
,but at the sixth hour two satellites   
only presented themselves to view in    
this position1 namely in the same       
straight line with ,jupiter exactly1 and
 the distance of the nearest to the     
planet was lengthened to #c2 the next   
was #b further off1 and unless ,i am    
mistaken1 the two satellites previously 
observed in the middle had come         
together1 and appeared as one4  ,jan4   
#be1 at #a h4 #dj m41 the satellites    
were grouped thus 7,fig4 #bd74 ,there   
were only two satellites on the east    
side1 and these were rather large4 ,the 
satellite furthest to the east was #e   
from the satellite in the middle1 and it
 was #f from ,jupiter4  ,jan4 #bf1 at #j
 h4 #dj m41 the relative positions of   
the satellites were thus 7,fig4 #be74   

,three satellites were in view1 of which
 two were east and the third west of    
,jupiter2 this one was distant #c from  
the planet4 ,on the east side the       
satellite in the middle was at a        
distance of #e #bj2 the further         
satellite was #f beyond2 they were      
arranged in a straight line1 and were of
 the same size4 ,at the fifth hour the  
arrangement was nearly the same1 with   
this difference only1 that the fourth   
satellite was emerging on the east side 
near ,jupiter4 ,it was smaller than the 
rest1 and was then at a distance of #j  
#cj from ,jupiter2 but was raised a     
little above the straight line towards  
the north1 as the accompanying figure   
shows 7,fig4 #bf74  ,jan4 #bg1 #a h4    
after sunset1 a single satellite only   
was in view1 and that on the east side  
of ,jupiter in this position 7,fig4     
#bg74 ,it was very small1 and at a      
distance of #g from ,jupiter4  ,jan4 #bh
 and #bi4--,owing to the intervention of
 clouds1 ,i could make no observation4  

,jan4 #cj4--;,at the first hour of the  
night the satellites were in view1      
arranged in the following way 7,fig4    
#bh74 ,there was one satellite on the   
east side1 at a distance of #b #cj from 
,jupiter2 and there were two satellites 
on the west1 of which the one nearer to 
,jupiter was #c off the planet1 and the 
other satellite #a further4 ,the places 
of the outer satellites and ,jupiter    
were in the same straight line2 but the 
satellite in the middle was a little    
above it to the north4 ,the satellite   
furthest to the west was smaller than   
the rest4  ,on the last day of the      
month1 at the second hour1 two          
satellites on the east side were        
visible1 and one on the west 7,fig4     
#bi74 ,of the satellites east of the    
planet1 the one in the middle was #b #bj
 distant from ,jupiter2 and the         
satellite further to the east was #j #cj
 from the middle satellite2 the         
satellite on the west was at a distance 
of #aj from ,jupiter4 ,they were in the 

same straight line nearly1 and would    
have been exactly so1 only the satellite
 on the east nearest to ,jupiter was    
raised a little towards the north4 ,at  
the fourth hour1 the two satellites on  
the east were still nearer together1 for
 they were only #bj apart 7,fig4 #cj74  
,the western satellite appeared rather  
small in these two observations4  ,feb4 
#a4--;,at the second hour of the night  
the arrangement was similar 7,fig4 #ca74
 ,the satellite furthest to the east was
 at a distance of #f from ,jupiter1 and 
the western satellite #h4 ,on the east  
side there was a very small satellite1  
at a distance of #bj from ,jupiter4     
,they made a perfectly straight line4   
,feb4 #b4--,the satellites were seen    
arranged thus 7,fig4 #cb74 ,there was   
one only on the east1 at a distance of  
#f from ,jupiter4 ,jupiter was #d from  
the nearest satellite on the west2      
between this satellite and the satellite
 further to the west there was an       
interval of #h2 they were in the same   

straight line exactly1 and were nearly  
of the same magnitude4 ,but at the      
seventh hour four satellites were       
there--two on each side of ,jupiter     
7,fig4 #cc74 ,of these satellites1 the  
most easterly was at a distance of #d   
from the next2 this satellite was #a #dj
 from ,jupiter2 ,jupiter was #f from the
 nearest satellite on the west1 and this
 one from the satellite further to the  
west1 #h2 and they were all alike in the
 same straight line1 drawn in the       
direction of the ,zodiac4  ,feb4 #c3 #g 
h4--,the satellites were arranged in the
 following way 7,fig4 #cd73--,the       
satellite on the east was at a distance 
of #a #cj from ,jupiter2 the nearest    
satellite on the west1 #b1 and there was
 a long distance1 #aj1 from this        
satellite to the satellite further to   
the west4 ,they were exactly in the same
 straight line1 and of equal magnitude4 
,feb4 #d3 #b h4--,four satellites       
attended ,jupiter1 two on the east and  
two on the west1 arranged in one        

perfectly straight line1 as in the      
adjoining figure 7,fig4 #ce74 ,the      
satellite furthest to the east was at a 
distance of #c from the next satellite4 
,this one was #j #dj from ,jupiter2     
,jupiter #d from the nearest satellite  
on the west2 and this one from the      
satellite further to the west #f4 ,in   
magnitude they were nearly equal2 the   
satellite nearest to ,jupiter was rather
 smaller in appearance than the rest4   
,but at the seventh hour 7,fig4 #cf7 the
 eastern satellites were at a distance  
of only #j #cj apart4 ,jupiter was #b   
from the nearest satellite on the east2 
and from the satellite on the west1 next
 in order1 #d2 this one was distant #c  
from the satellite further to the west4 
,they were all equal in magnitude1 and  
in a straight line1 drawn in the        
direction of the ecliptic4  ,feb4       
#e4--,the sky was cloudy4  ,feb4        
#f4--,two satellites only appeared1 with
 ,jupiter between them1 as is seen in   
the accompanying figure 7,fig4 #cg74    

,the satellite on the east was #b from  
,jupiter1 and that on the west #c4 ,they
 were in the same straight line with    
,jupiter1 and were equal in magnitude4  
,feb4 #g4--,there were two satellites by
 the side of ,jupiter1 and both of them 
on the east of the planet1 arranged in  
this manner 7,fig4 #ch74 ,the intervals 
between the satellites and ,jupiter were
 equal1 and of #a each2 and a straight  
line would go through them and the      
centre of ,jupiter4  ,feb4 #h3 #a       
h4--,three satellites were there1 all on
 the east side of ,jupiter1 as in the   
diagram 7,fig4 #ci74 ,the nearest to    
,jupiter1 a rather small one1 was       
distant from the planet #a #bj2 the     
middle one was #d from this satellite1  
and was rather large2 the satellite     
furthest to the east1 a very small one1 
was at a distance of #j #bj from this   
satellite4 ,it was doubtful whether     
there was one satellite near to ,jupiter
 or two1 for sometimes it seemed that   
there was another satellite by its side 

towards the east1 wonderfully small1 and
 only #aj from it4 ,they were all       
situated at points in a straight line   
drawn in the direction of the ,zodiac4  
,at the third hour the satellite nearest
 to ,jupiter was almost touching the    
planet1 for it was only distant #aj from
 it2 but the others had become further  
off1 for the middle one was #f from     
,jupiter4 ,at length1 at the fourth     
hour1 the satellite which was previously
 the nearest to ,jupiter joined with the
 planet and disappeared4  ,feb4 #i3 #j  
h4 #cj m4--,there were two satellites on
 the east side of ,jupiter1 and one on  
the west1 in an arrangement such as this
 7,fig4 #dj74 ,the satellite furthest to
 the east1 which was a rather small one1
 was distant #d from the next satellite2
 the satellite in the middle was larger1
 and at a distance of #g from ,jupiter4 
,jupiter was distant #d from the western
 satellite1 which was a small one4      
,feb4 #aj3 #a h4 #cj m4--,a pair of     
satellites1 very small1 and both on the 

east of the planet1 were visible1 in the
 following position 7,fig4 #da74 ,the   
further satellite was distant from      
,jupiter #aj1 the nearer #j #bj1 and    
they were in the same straight line2 but
 at the fourth hour the satellite       
nearest to ,jupiter no longer appeared1 
and the other seemed so diminished that 
it could scarcely be kept in sight1     
although the atmosphere was quite clear1
 and the satellite was further from     
,jupiter than before1 since its distance
 was now #ab4  ,feb4 #aa3 #a h4--,there 
were two satellites on the east1 and one
 on the west 7,fig4 #db74 ,the western  
satellite was at a distance of #d from  
,jupiter4 ,the satellite on the east1   
nearest to the planet1 was likewise #d  
from ,jupiter2 but the satellite further
 to the east was at a distance from this
 one of #h2 they were fairly clear to   
view1 and in the same straight line2 but
 at the third hour the fourth satellite 
was visible near to ,jupiter on the     
east1 less in magnitude than the rest1  

separated from ,jupiter by a distance of
 #j #cj1 and slightly to the north out  
of the straight line drawn through the  
rest 7,fig4 #dc74 ,they were all very   
bright and extremely distinct1 but at #e
 h4 #cj m4 the satellite on the east    
nearest to ,jupiter had moved further   
away from the planet1 and was occupying 
a position midway between the planet and
 the neighbouring satellite further to  
the east4 ,they were all in the same    
straight line exactly1 and of the same  
magnitude1 as may be seen in the        
accompanying diagram 7,fig4 #dd74  ,feb4
 #ab3 #j h4 #dj m4--,a pair of          
satellites on the east1 a pair likewise 
on the west1 were near the planet 7,fig4
 #de74 ,the satellite on the east       
furthest removed from ,jupiter was at a 
distance of #aj1 and the further of the 
satellites on the west was #h off4 ,they
 were both fairly distinct4 ,the other  
two were very near to ,jupiter1 and very
 small1 especially the satellite to the 
east1 which was at a distance of #j #dj 

from ,jupiter4 ,the distance of the     
western satellite was #a4 ,but at the   
fourth hour the satellite which was     
nearest to ,jupiter on the east was     
visible no longer4  ,feb4 #ac3 #j h4 #cj
 m4--,two satellites were visible in the
 east1 two also in the west 7,fig4 #df74
 ,the satellite on the east near        
,jupiter was fairly distinct2 its       
distance from the planet was #b4 ,the   
satellite further to the east was less  
noticeable2 it was distant #d from the  
other4 ,of the satellites on the west1  
the one furthest from ,jupiter1 which   
was very distinct1 was parted from the  
planet #d4 ,between this satellite and  
,jupiter intervened a small satellite   
close to the most westerly satellite1   
being not more than #j #c off4 ,they    
were all in the same straight line1     
corresponding exactly to the direction  
of the ecliptic4  ,feb4 #ae 7for on the 
#adth the sky was covered with clouds71 
at the first hour1 the position of the  
satellites was thus 7,fig4 #dg72 that   

is1 there were three satellites on the  
east1 but none were visible on the west4
 ,the satellite on the east nearest to  
,jupiter was at a distance of #j #ej    
from the planet2 the next in order was  
#j #bj from this satellite1 and the     
furthest to the east was #b from the    
second satellite1 and it was larger than
 the others1 for those nearer to        
,jupiter were very small4 ,but about the
 fifth hour only one of the satellites  
which had been near to ,jupiter was to  
be seen2 its distance from ,jupiter was 
#j #cj4 ,the distance of the satellite  
furthest to the east from ,jupiter had  
increased1 for it was then #d 7,fig4    
#dh74 ,but at the sixth hour1 besides   
the two situated as just described on   
the east1 one satellite was visible     
towards the west1 very small1 at a      
distance of #b from ,jupiter 7,fig4     
#di74  ,feb4 #af3 #f h4--,their places  
were arranged as follows 7,fig4 #ej72   
that is1 the satellite on the east was  
#g from ,jupiter1 ,jupiter #e from the  

next satellite on the west1 and this #c 
from the remaining satellite still      
further to the west4 ,they were all of  
the same magnitude nearly1 rather       
bright1 and in the same straight line1  
corresponding accurately to the         
direction of the ,zodiac4  ,feb4 #ag3 #a
 h4--,two satellites were in view1 one  
on the east1 distant #c from ,jupiter2  
the other on the west1 distant #aj      
7,fig4 #ea74 ,the latter was somewhat   
less than the satellite on the east2 but
 at the sixth hour the eastern satellite
 was nearer to ,jupiter1 being at a     
distance of #j #ej1 and the western     
satellite was further off1 namely #ab4  
,at both observations they were in the  
same straight line with ,jupiter1 and   
were both rather small1 especially the  
eastern satellite in the second         
observation4  ,feb4 #ah3 #a h4--,three  
satellites were in view1 of which two   
were on the west and one on the east2   
the distance of the eastern satellite   
from ,jupiter was #c1 and of the nearest

 satellite on the west #b2 the remaining
 satellite1 still further to the west1  
was #h from the middle satellite 7,fig4 
#eb74 ,they were all in the same        
straight line exactly1 and of about the 
same magnitude4 ,but at the second hour 
the satellites nearest to the planet    
were at equal distances from ,jupiter1  
for the western satellite was now also  
#c from the planet4 ,but at the sixth   
hour the fourth satellite was visible   
between the satellite on the east and   
,jupiter1 in the following configuration
 7,fig4 #ec74 ,the satellite furthest to
 the east was at a distance of #c from  
the next in order2 this one was at a    
distance of #a #ej from ,jupiter2       
,jupiter was at a distance of #c from   
the next satellite on the west1 and this
 #g from the satellite still further to 
the west4 ,these were nearly equal in   
magnitude1 only the satellite on the    
east nearest to ,jupiter was a little   
smaller than the rest1 and they were all
 in the same straight line parallel to  

the ecliptic4  ,feb4 #ai3 #j h4 #dj     
m4--,two satellites only were in view1  
west of ,jupiter1 rather large1 and     
arranged exactly in the same straight   
line with ,jupiter1 in the direction of 
the ecliptic 7,fig4 #ed74 ,the nearer   
satellite was at a distance of #g from  
,jupiter and of #f from the satellite   
further to the west4  ,feb4 #bj4--,the  
sky was cloudy4  ,feb4 #ba3 #a h4 #cj   
m4--,three satellites1 rather small1    
were in view1 placed thus 7,fig4 #ee74  
,the satellite to the east was #b from  
,jupiter2 ,jupiter was #c from the next1
 which was on the west2 and this one was
 #g from the satellite further to the   
west4 ,they were exactly in the same    
straight line parallel to the ecliptic4 
,feb4 #be3 #a h4 #cj m4 7for on the     
three previous nights the sky was       
overcast74--,three satellites appeared1 
two on the east1 which were at a        
distance of #d apart1 the same as the   
distance of the nearer satellite from   
,jupiter2 on the west there was one     

satellite at a distance of #b from      
,jupiter4 ,they were exactly in the same
 straight line in the direction of the  
ecliptic 7,fig4 #ef74  ,feb4 #bf3 #j h4 
#cj m4--,a pair of satellites only were 
present1 one on the east1 distant #aj   
from ,jupiter2 the other was on the     
west1 at a distance of #f 7,fig4 #eg74  
,the eastern satellite was slightly     
smaller than the western4 ,at the fifth 
hour three satellites were visible2 for1
 besides the two already noticed1 a     
third satellite was in view1 on the     
west1 near ,jupiter1 very small1 which  
previously had been hidden behind       
,jupiter1 and it was at a distance of #a
 from the planet 7,fig4 #eh74  ,but the 
satellite on the east was seen to be    
further off than before1 being at a     
distance of #aa from ,jupiter4 ,on this 
night1 for the first time1 ,i determined
 to observe the motion of ,jupiter and  
the adjacent planets 7his satellites7   
along the zodiac1 by reference to some  
fixed star2 for there was a fixed star  

in view1 eastwards of ,jupiter1 at a    
distance of #aa from the satellite on   
the east1 and a little to the south1 in 
the following manner 7,fig4 #ei74  ,feb4
 #bg3 #a h4 #d m4--,the satellites      
appeared in the following configuration4
 ,the satellite furthest to the east was
 at a distance of #aj from ,jupiter2 the
 next in order was near ,jupiter1 being 
at a distance of #j #cj from the planet4
 ,the next satellite was on the western 
side1 at a distance of #b #cj from      
,jupiter2 and the satellite further to  
the west was at a distance of #a from   
this4 ,the two satellites near to       
,jupiter appeared small1 especially the 
satellite on the east2 but the          
satellites furthest off were very       
bright1 particularly that on the west1  
and they made a straight line in the    
direction of the ecliptic exactly4 ,the 
motion of the planets towards the east  
was plainly seen by reference to the    
aforesaid fixed star1 for ,jupiter and  
his attendant satellites were nearer to 

it1 as may be seen in the accompanying  
figure 7,fig4 #fj74 ,at the fifth hour  
the satellite on the east1 near to      
,jupiter1 was #a from the planet4  ,feb4
 #bh3 #a h4--,only two satellites were  
visible1 one on the east1 at a distance 
of #i from ,jupiter1 and another on the 
west1 at a distance of #b2 they were    
both rather bright1 and in the same     
straight line with ,jupiter1 and a      
straight line drawn from the fixed star 
perpendicular to this straight line fell
 upon the satellite on the east1 as in  
the figure 7,fig4 #fa74 ,at the fifth   
hour a third satellite was seen at a    
distance of #b from ,jupiter1 on the    
east1 in the position shown in the      
figure 7,fig4 #fb74  ,march #a3 #j h4   
#dj m4--,four satellites1 all on the    
east of the planet1 were seen2 the      
satellite nearest to ,jupiter was #b    
from the planet2 the next #a from this2 
the third was #j #bj from the second1   
and was brighter than the others2 and   
the satellite still further to the east 

was at a distance of #d from it1 and was
 smaller than the others 7,fig4 #fc74   
,they made a straight line very nearly1 
only the satellite third from ,jupiter  
was slightly above the line4 ,the fixed 
star formed with ,jupiter and the most  
easterly satellite an equilateral       
triangle1 as in the figure4  ,march #b3 
#j h4 #dj m4--,three satellites were in 
attendance1 two on the east and one on  
the west1 in the configuration shown in 
the diagram 7,fig4 #fd74 ,the satellite 
furthest to the east was #g from        
,jupiter2 from this satellite the next  
was distant #j #cj1 and the satellite on
 the west was separated from ,jupiter by
 an interval of #b4 ,the satellites     
furthest off were brighter and larger   
than the remaining satellite1 which     
appeared very small4 ,the satellite     
furthest to the east seemed to be raised
 a little towards the north1 out of the 
straight line drawn through the other   
satellites and ,jupiter4  ,the fixed    
star already noticed was at a distance  

of #h from the western satellite1 that  
is1 from the perpendicular drawn from   
that satellite to the straight line     
drawn through all the system1 as shown  
in the figure given4  ,these            
determinations of the motion of ,jupiter
 and the adjacent planets 7his          
satellites7 by reference to a fixed     
star1 ,i have thought well to present to
 the notice of astronomers1 in order    
that any one may be able to understand  
from them that the movements of these   
planets 7,jupiter's satellites7 both in 
longitude and in latitude agree exactly 
with the motions of ,jupiter which are  
extracted from tables4  ,these are my   
observations upon the four ,medicean    
planets1 recently discovered for the    
first time by me2 and although it is not
 yet permitted me to deduce by          
calculation from these observations the 
orbits of these bodies1 yet ,i may be   
allowed to make some statements1 based  
upon them1 well worthy of attention4    
,sidenote3 ,deductions from the previous

 observations concerning the orbits and 
periods of ,jupiter's satellites4  ,and1
 in the first place1 since they are     
sometimes behind1 sometimes before      
,jupiter1 at like distances1 and        
withdraw from this planet towards the   
east and towards the west only within   
very narrow limits of divergence1 and   
since they accompany this planet alike  
when its motion is retrograde and       
direct1 it can be a matter of doubt to  
no one that they perform their          
revolutions about this planet1 while at 
the same time they all accomplish       
together orbits of twelve years' length 
about the centre of the world4          
,moreover1 they revolve in unequal      
circles1 which is evidently the         
conclusion to be drawn from the fact    
that ,i have never been permitted to see
 two satellites in conjunction when     
their distance from ,jupiter was great1 
whereas near ,jupiter two1 three1 and   
sometimes all 7four71 have been found   
closely packed together4 ,moreover1 it  

may be detected that the revolutions of 
the satellites which describe the       
smallest circles round ,jupiter are the 
most rapid1 for the satellites nearest  
to ,jupiter are often to be seen in the 
east1 when the day before they have     
appeared in the west1 and contrariwise4 
,also the satellite moving in the       
greatest orbit seems to me1 after       
carefully weighing the occasions of its 
returning to positions previously       
noticed1 to have a periodic time of half
 a month4#ag ,besides1 we have a notable
 and splendid argument to remove the    
scruples of those who can tolerate the  
revolution of the planets round the ,sun
 in the ,copernican system1 yet are so  
disturbed by the motion of one ,moon    
about the ,earth1 while both accomplish 
an orbit of a year's length about the   
,sun1 that they consider that this      
theory of the constitution of the       
universe must be upset as impossible2   
for now we have not one planet only     
revolving about another1 while both     

traverse a vast orbit about the ,sun1   
but our sense of sight presents to us   
four satellites circling about ,jupiter1
 like the ,moon about the ,earth1 while 
the whole system travels over a mighty  
orbit about the ,sun in the space of    
twelve years4      #ag ,in the edition  
of ,galileo's works published at        
,florence1     #ahed1 there are given   
the tables of the hourly movements of   
the     satellites of ,jupiter1 from    
which ,galileo determined their periods 
of revolution4 ,in the beginning of his 
treatise on floating bodies1            
,discorso intorno i ,galleggianti1      
#afaa-ab1 ,galileo gives the times      
of rotation as approximately1 7i47 #a d4
 #ah-a_/b h42 7ii47 #c d4     #ac-a_/c  
h42 7iii47 #g d4 #d h42 7iv47 #af d4 #ah
 h42 he also published                  
configurations of the satellites        
calculated for ,march1 ,april1     and a
 part of ,may #afac4 ,the periodic times
 of the satellites1 as     corrected by 
later observers1 are1 7i47 #a d4 #ah h4 

#bh m42 7ii47 #c     d4 #ac h4 #ae m42  
7iii47 #g d4 #c h4 #dc m42 7iv47 #af d4 
#af h4 #cb m4  ,sidenote3 ,explanation  
of the variations in brightness of      
,jupiter's satellites4  ,lastly1 ,i must
 not pass over the consideration of the 
reason why it happens that the ,medicean
 stars1 in performing very small        
revolutions about ,jupiter1 seem        
sometimes more than twice as large as at
 other times4 ,we can by no means look  
for the explanation in the mists of the 
,earth's atmosphere1 for they appear    
increased or diminished1 while the discs
 of ,jupiter and neighbouring fixed     
stars are seen quite unaltered4 ,that   
they approach and recede from the ,earth
 at the points of their revolutions     
nearest to and furthest from the ,earth 
to such an extent as to account for so  
great changes seems altogether          
untenable1 for a strict circular motion 
can by no means show those phenomena2   
and an elliptical motion 7which in this 
case would be nearly rectilinear7 seems 

to be both untenable and by no means in 
harmony with the phenomena observed4    
,but ,i gladly publish the explanation  
which has occurred to me upon this      
subject1 and submit it to the judgment  
and criticism of all true philosophers4 
,it is certain that when atmospheric    
mists intervene the ,sun and ,moon      
appear larger1 but the fixed stars and  
planets less than they really are2 hence
 the former luminaries1 when near the   
horizon1 are larger than at other times1
 but stars appear smaller1 and are      
frequently scarcely visible2 also they  
are still more diminished if those mists
 are bathed in light2 so stars appear   
very small by day and in the twilight1  
but the ,moon does not appear so1 as ,i 
have previously remarked4 ,moreover1 it 
is certain that not only the ,earth1 but
 also the ,moon1 has its own vaporous   
sphere enveloping it1 for the reasons   
which ,i have previously mentioned1 and 
especially for those which shall be     
stated more fully in my ,system2 and we 

may consistently decide that the same is
 true with regard to the rest of the    
planets2 so that it seems to be by no   
means an untenable opinion to place     
round ,jupiter also an atmosphere denser
 than the rest of the ether1#ah about   
which1 like the ,moon about the sphere  
of the elements1 the ,medicean planets  
7,jupiter's satellites7 revolve2 and    
that by the intervention of this        
atmosphere they appear smaller when they
 are in apogee2 but when in perigee1    
through the absence or attenuation of   
that atmosphere1 they appear larger4    
,want of time prevents my going further 
into these matters2 my readers may      
expect further remarks upon these       
subjects in a short time4      #ah      
,modern astronomers agree in assigning  
an atmosphere to     ,jupiter1 but      
consider it not extensive enough to     
affect the     brightness of the        
satellites4--7,,webb1 ,celestial        
,objects for ,common     ,telescopes47  
,their absolute magnitudes are          

different1 and their     surfaces have  
been observed to be obscured by spots1  
which may     account for the variations
 of their brightness4 ,these spots1 like
     the lunar spots1 are probably due  
to variations of reflective     power at
 different parts of their surfaces1 for 
as they always     turn the same face to
 ,jupiter1 they present different       
portions of     their surfaces to us    
periodically1 and it has been           
ascertained     by observation that     
8these fluctuations in their brightness 
are     periodical1 depending on their  
position with respect to the            
,sun40--7,,herschel1 ,outlines of       
,astronomy2 ,,arago1 ,astronomie        
,populaire1 #ahed47  ,original          
,configurations of ,jupiter's           
,satellites observed by ,galileo in the 
months of ,january1 ,february1 and      
,march #afaj1 and published with the    
#ast edition of his book ,sidereus      
,nuncius1 ,venice1 #afaj4               
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,star4                                  
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,star                                   

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,mar4    #a                             
,star                                   
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----------------------         ,a ,,part
 ,,of ,,the ,,preface ,,to              
,,kepler',s ,,dioptrics      ,,forming  
,a ,,continuation ,,of ,,galileo',s     
,,sidereal ,,messenger4       ,in the   
preface to ,kepler's ,dioptrics there   
are introduced letters     of ,galileo  
about the new and astonishing           
discoveries which he     had made in the

 heavens by the aid of the telescope    
since the     publication of his work1  
,the ,sidereal ,messenger4 ,the portion 
of the preface which refers to ,galileo1
 containing these letters     and       
,kepler's remarks upon them1 is added   
here1 as continuing the     original    
account of ,galileo's astronomical      
discoveries4   ,extract from the        
,preface of ,kepler's ,dioptrics4       
,augsburg1 #afaa4   ,sidenote3 ,kepler  
remarks on the importance of the        
application of the telescope to         
astronomical investigations as indicated
 by ,galileo's discoveries1 published in
 his ,sidereal ,messenger4  8,the       
,sidereal ,messenger0 of ,galileo has   
been for a long time in everybody's     
hands1 also my 8,discussion1 such as it 
is1 with this ,messenger10 and my ,brief
 ,narrative in confirmation of          
,galileo's ,sidereal ,messenger1 so any 
reader may briefly weigh the chief      
points of that ,messenger and see the   
nature and the value of the discoveries 

made by the aid of the telescope1 the   
theory of which ,i am intending to      
demonstrate in this treatise4 ,actual   
sight testified that there is a certain 
bright heavenly body which we call the  
,moon4 ,it was demonstrated from the    
laws of optics that this body is round2 
also ,astronomy1 by some arguments      
founded upon optics1 had built up the   
conclusion that its distance from the   
earth is about sixty semi-diameters of  
the earth4 ,various spots showed        
themselves in that body2 and the result 
was a dubious opinion among a few       
philosophers1 derived from ,hecatus'    
account of the stories about the island 
of the ,hyperboreans1#ai that the       
reflected images of mountains and       
valleys1 sea and land1 were seen there2 
but now the telescope places all these  
matters before our eyes in such a way   
that he must be an intellectual coward  
who1 while enjoying such a view1 still  
thinks that the matter is open to doubt4
 ,nothing is more certain than that the 

southern parts of the moon teem with    
mountains1 very many in number1 and vast
 in size2 and that the northern parts1  
inasmuch as they are lower1 receive in  
most extensive lakes the water flowing  
down from the south4 ,the conclusions   
which previously ,pena published as     
disclosed by the aid of optics1 started 
indeed from certain slight supports1    
rather than foundations1 afforded by    
actual sight1 but were proved by long   
arguments depending one upon another1 so
 that they might be assigned to human   
reason rather than to sight2 but now our
 very eyes1 as if a new door of heaven  
had been opened1 are led to the view of 
matters once hidden from them4 ,but if  
it should please any one to exhaust the 
force of reasoning upon these new       
observations1 who does not see how far  
the contemplation of nature will extend 
her boundaries1 when we ask1 8,what is  
the use of the tracts of mountains and  
valleys1 and the very wide expanse of   
seas in the moon80 and 8,may not some   

creature less noble than man be imagined
 such as might inhabit those tracts80   
#ai ,diodorus ,siculus1 ii4 #dg4  ,with 
no less certainty also do we decide by  
the use of this instrument even that    
famous question1 which1 coeval with     
philosophy itself1 is disputed to this  
day by the noblest intellects--,i mean1 
whether the earth can move 7as the      
theory of the ,planets greatly requires7
 without the overthrow of all bodies    
that have weight1 or the confusion of   
the motion of the elements8 ,for if the 
earth were banished from the centre of  
the universe1 some fear lest the water  
should leave the orb of the earth and   
flow to the centre of the universe2 and 
yet we see that in the moon1 as well as 
in the earth1 there is a quantity of    
moisture occupying the sunken hollows of
 that globe2 and although this orb      
revolves actually in the ether1 and     
outside the centres not merely of the   
universe1 but even of our earth1 yet the
 mass of water in the moon is not at all

 hindered from cleaving invariably to   
the orb of the moon1 and tending to the 
centre of the body to which it belongs4 
,so1 by this instance of the phenomena  
of the moon1 the science of optics      
amends the received theory of mechanics1
 and confirms on this point my          
introduction to my ,commentaries upon   
the ,motions of the ,planet ,mars4#bj   
#bj ,kepler says in his introduction to 
his ,commentaries upon     the ,motions 
of the ,planet ,mars1 that the theory of
 gravitation     depends on certain     
axioms1 one of which is that 8heavy     
bodies do     not tend to the centre of 
the universe1 supposing the earth to be 
placed there1 because that point is the 
centre of the universe1     but because 
it is the centre of the earth4 ,so1     
wherever the earth     be set1 or       
whithersoever it be transported1 heavy  
bodies have a     continual tendency to 
it40 ,kepler's object in this work was  
to     correct the methods for          
determining the apparent places of the  

planets according to the three theories 
then current--the ,ptolemaic1     the   
,copernican1 and that of ,tycho ,brahe4 
,in #aeic the observed place of the     
planet ,mars differed by nearly     #e  
from the place calculated for it4       
,kepler accordingly studied     the     
motions of this planet1 and 8by most    
laborious demonstrations     and        
discussions of many observations10      
arrived at the conclusions     known as 
,kepler's first and second laws2        
according to which the     ,copernican  
system of eccentrics and epicycles was  
replaced by an     ellipse whose centre 
and eccentricity were the same as the   
centre     and eccentricity of the      
eccentric in the older method1 and the  
,sun     therefore was in one of the    
foci4 ,also the motion of the planet in 
its orbit was such that equal areas were
 described about the ,sun by     the    
radius vector of the planet in equal    
times4--,,kepler1 ,astronomia     ,nova 
7,prague71 #afji4  ,the followers of the

 ,samian philosophy 7for ,i may use this
 epithet to designate the philosophy    
originated by the ,samians1 ,pythagoras 
and ,aristarchus7 have a strong argument
 against the apparent immobility of the 
earth provided in the phenomena of the  
moon4 ,for we are taught by optics that 
if any one of us was in the moon1 to him
 the moon1 his abode1 would seem quite  
immovable1 but our earth and sun and all
 the rest of the heavenly bodies        
movable2 for the conclusions of sight   
are thus related4  ,pena has noticed how
 astronomers1 using the principles of   
optics1 have by most laborious reasoning
 removed the ,milky ,way from the       
elementary universe1 where ,aristotle   
had placed it1 into the highest region  
of the ether2 but now1 by the aid of the
 telescope lately invented1 the very    
eyes of astronomers are conducted       
straight to a thorough survey of the    
substance of the ,milky ,way2 and       
whoever enjoys this sight is compelled  
to confess that the ,milky ,way is      

nothing else but a mass of extremely    
small stars4  ,again1 up to this time   
the nature of nebulous stars had been   
entirely unknown2 but if the telescope  
be directed to one of such nebulous     
balls1 as ,ptolemy calls them1 it again 
shows1 as in the case of the ,milky     
,way1 three or four very bright stars   
clustered very close together4  ,again1 
who without this instrument would have  
believed that the number of the fixed   
stars was ten times1 or perhaps twenty  
times1 more than that which is given in 
,ptolemy's description of the fixed     
stars8 ,and whence1 pray1 should we seek
 for conclusive evidence about the end  
or boundary of this visible universe1   
proving that it is actually the sphere  
of the fixed stars1 and that there is   
nothing beyond1 except from this very   
discovery by the telescope of this      
multitude of fixed stars1 which is1 as  
it were1 the vaulting of the mobile     
universe8 ,again1 how greatly an        
astronomer would go wrong in determining

 the magnitude of the fixed stars1      
except he should survey the stars all   
over again with a telescope1 also may be
 seen in ,galileo's treatise1 and we    
will also hereafter produce in proof a  
letter from a ,german astronomer4  ,but 
no words can express my admiration of   
that chapter of the ,sidereal ,messenger
 where the story is told of the         
discovery1 by the aid of a very highly  
finished telescope1 of another world1 as
 it were1 in the planet ,jupiter4 ,the  
mind of the philosopher almost reels as 
he considers that there is a vast orb1  
which is equal in mass to fourteen orbs 
like the earth 7unless on this point the
 telescope of ,galileo shall shortly    
reveal something more exact than the    
measurements of ,tycho ,brahe7 round    
which circle four moons1 not unlike this
 moon of ours2 the slowest revolving in 
the space of fourteen of our days1 as   
,galileo has published2 the next to     
this1 by far the brightest of the four1 
in the space of eight days1 as ,i       

detected in last ,april and ,may2 the   
other two in still shorter periods4 ,and
 here the reasoning of my ,commentaries 
about the ,planet ,mars1 applied to a   
similar case1 induces me to conclude    
also that the actual orb of ,jupiter    
rotates with very great rapidity1 most  
certainly faster than once in the space 
of one of our days2 so that this        
rotation of the mighty orb upon its own 
axis is accompanied wherever it goes by 
the perpetual circuits of those four    
moons4 ,moreover1 this sun of ours1 the 
common source of heat and light for this
 terrestrial world as well as for that  
world of ,jupiter1 which we consider to 
be of the angular magnitude of #cj at   
most1 there scarcely subtends more than 
#f or #g1 and is found again in the same
 position among the fixed stars1 having 
completed the zodiac in the interval1   
after a period of twelve of our         
years4#ba ,accordingly1 the creatures   
which live on that orb of ,jupiter1     
while they contemplate the very swift   

courses of those four moons among the   
fixed stars1 while they behold them and 
the sun rising and setting day by day1  
would swear by ,jupiter-in-stone1 like  
the ,romans 7for ,i have lately returned
 from those parts71 that their orb of   
,jupiter remains immovable in one spot1 
and that the fixed stars and the sun1   
which are the bodies really at rest1 no 
less than those four moons of theirs1   
revolve round that abode of theirs with 
manifold variety of motions4 ,and from  
this instance now1 much more than before
 from the instance of the moon1 any     
follower of the ,samian philosophy will 
learn what reply may be made to any one 
objecting to the theory of the motion of
 the earth as absurd1 and alleging the  
evidence of our sight4 ,o telescope1    
instrument of much knowledge1 more      
precious than any sceptre6 ,is not he   
who holds thee in his hand made king and
 lord of the works of ,god8 ,truly      
8,all that is overhead1 the mighty orbs 
,with all their motions1 thou dost      

subjugate     ,to man's intelligence40  
,if there is any one in some degree     
friendly to ,copernicus and the lights  
of the ,samian philosophy1 who finds    
this difficulty only1 that he doubts how
 it can happen1 supposing the earth to  
perform again and again her course among
 the planets through the ethereal       
plains1 that the moon should keep so    
constantly by her side1 like an         
inseparable companion1 and at the same  
time fly round and round the actual orb 
of the earth1 just like a faithful dog  
which goes round and round his master on
 some journey1 now running in front1 now
 deviating to this side or that1 in     
ever-varying mazes1 let him look at the 
planet ,jupiter1 which1 as this         
telescope shows1 certainly carries in   
its train not one such companion only1  
like the earth1 as ,copernicus showed1  
but actually four1 that never leave it1 
though all the time hastening each in   
its own orbit4      #ba ,the degree of  
accuracy attained by ,kepler and        

,galileo with     their imperfect       
instruments will be appreciated by      
comparing     these statements with the 
determinations of later astronomers4    
,jupiter is about #acjj times the size  
of the ,earth4 ,its diameter is         
about #hg1jjj miles2 time of rotation1  
#i h4 #ee m4 #ba sec42 time of          
revolution1 #dccc days nearly4 ,the     
angular diameter of the sun1 seen       
from ,jupiter1 is between #f and #g4    
,the times of revolution of the     four
 satellites are1 as already given3 7i47 
#a d4 #ah h4 #bh m41 7ii47     #c d4 #ac
 h4 #ae m41 7iii47 #g d4 #c h4 #dc m41  
7iv47 #af d4 #af h4 #cb m4  ,but enough 
has been said about these matters in my 
,discussion with the ,sidereal          
,messenger4 ,it is time that ,i should  
turn to those discoveries which have    
been made since the publication of      
,galileo's ,sidereal ,messenger1 and    
since my ,discussion with it1 by means  
of this telescope4  ,sidenote3          
,galileo's discovery of ,saturn's ring  

7imperfectly74  ,it is now just a year  
since ,galileo wrote to ,prague1 and    
gave full notice that he had detected   
something new in the heavens beyond his 
former discoveries2 and that there might
 not be any one who1 with the intention 
of detracting from his credit1 should   
try to pass himself off as an earlier   
observer of the phenomenon1 ,galileo    
gave a certain space of time for the    
publication of the new phenomena which  
any one had seen2 he himself meanwhile  
described his discovery in letters      
transposed in this manner3 s m a i s m r
 m i l m e p o e t a l e u m i b u n e n
 u g t t a u i r a s4 ,out of these     
letters ,i made an uncouth verse which  
,i inserted in my ,short ,account in the
 month of ,september of last year3--    
,salve umbistineum#bb geminatum ,martia 
proles4       ,hail1 twin companionship1
 children of ,mars4      #bb            
,umbistineum4 ,apparently this is some  
,german word with a     ,latin ending1  
such as um-bei-stehn2 ,kepler fancied   

that ,galileo     had discovered two    
satellites of ,mars4  ,but ,i was a very
 long way from the meaning of the       
letters2 it contained nothing to do with
 ,mars2 and1 not to detain you1 reader1 
here is the solution of the riddle in   
the words of ,galileo himself1 the      
author of it3#bc--      8,di ,firenze li
 #ac di ,novembre #afaj4--,ma passando  
ad altro1 giacch     il ,sig4 ,keplero  
ha in questa sua ultima narrazione      
stampate le     lettere che io mandai   
trasposte a ,vostra ,signoria           
,illustrissima     e ,reverendissima    
venendomi anco significato come ,sua    
,maest     ne desidera il senso1 ecco   
che io lo mando a ,vostra ,signoria     
,illustrissima per participarlo con ,sua
 ,maest col ,sig4 ,keplero e     con chi
 piacer a ,vostra ,signoria             
,illustrissima bramando io che     lo   
sappia ognuno4 ,le lettere dunque       
combinate nel lor vero senso     dicono 
cos1          ,altissimum planetam      
tergeminum observavi4      ,questo 1 che

 ,saturno con mia grandissima           
ammirazione ho osservato     essere non 
una stella sola1 ma tre insieme1 le     
quali quasi si     toccano2 e sono tr di
 loro totalmente immobili1 e constituite
     in questa guisa oo4 ,quella di     
mezzo  assai pi grande delle            
laterali2 sono situate una da oriente1  
l'altra da occidente1 nella     medesima
 linea retta a capello2 non sono        
giustamente secondo la     dirittura del
 ,zodiaco1 ma l'occidentale si eleva    
alquanto verso     ,borea2 forse sono   
parallele all',equinoziale4 ,se si      
guarderanno     con un occhiale che non 
sia di grandissima moltiplicazione1 non 
appariranno tre stelle ben distinte1 ma 
parr1 che ,saturno sia una     stella   
lunghetta in forma di un'oliva1 cos1 4  
,ma servendosi     di un occhiale che   
moltiplichi pi di mille volte in        
superficie1     si vedranno tre globi   
distintissimi1 che quasi si toccano1 non
     apparendo tr essi maggior divisione
 di un sottil filo oscuro4 ,or     ecco 

trovata la corte a ,giove1 e due ,servi 
a questo ,vecchio che     l'aiutano a   
camminare n mai se gli staccano dal     
fianco4 ,intorno     agli altri ,pianeti
 non ci  novit alcuna1 ec40      #bc    
,the text of the four letters of        
,galileo followed here is that     given
 in the edition of ,galileo's works     
published at ,florence1     #ahdb-ef2   
that in the edition of ,kepler's        
,dioptrics1 published at     ,augsburg1 
#afaa1 is very inaccurate4 ,these       
letters were written to     ,giuliano   
de' ,medici1 ambassador of the          
,grand-,duke of ,tuscany to the         
,emperor ,rudolf ,,ii4 at ,prague4      
,although these words differ little from
 ,latin1 yet ,i will translate them that
 no difficulty may hinder my reader from
 following me4 ,thus then ,galileo      
writes3--8,but to come now to my second 
topic4 ,since ,kepler has published in  
that recent #8,narrative' of his the    
letters which ,i sent as an anagram to  
your illustrious ,lordship1 and since an

 intimation has been given me that his  
,majesty desires to be taught the       
meaning of those letters1 ,i send it to 
your illustrious ,lordship1 that your   
,lordship may communicate it to his     
,majesty1 to ,kepler1 and to any one    
your ,lordship may wish4  8,the letters 
when joined together as they ought to   
be1 say this1     #8,altissimum planetam
 tergeminum observavi1'     #8,i have   
observed the most distant of the planets
 to have a triple     form4'      8,for 
in truth ,i have found out with the most
 intense surprise     that the planet   
,saturn is not merely one single star1  
but three     stars very close together1
 so much so that they are all but in    
contact one with another4 ,they are     
quite immovable with regard to     each 
other1 and are arranged in this manner1 
oo4 ,the middle star     of the three is
 by far greater than the two on either  
side4 ,they     are situated one towards
 the east1 the other towards the west1  
in     one straight line to a           

hair's-breadth2 not1 however1 exactly in
     the direction of the ,zodiac1 for  
the star furthest to the west     rises 
somewhat towards the north2 perhaps they
 are parallel to     the equator4 ,if   
you look at them through a glass that   
does not     multiply much1 the stars   
will not appear clearly separate from   
one     another1 but ,saturn's orb will 
appear somewhat elongated1 of the       
shape of an olive1 thus1 4 ,but if you  
should use a glass which     multiplies 
a surface more than a thousand times1   
there will appear     very distinctly   
three orbs1 almost touching one another2
 and they     will be thought to be not 
farther apart than the breadth of a very
     fine and scarcely visible thread4  
,so you see a guard of satellites       
has been found for ,jupiter1 and for the
 decrepit little old man two            
servants to help his steps and never    
leave his side4 ,concerning the     rest
 of the planets ,i have found nothing   
new40  ,so says ,galileo2 but if ,i may 

do so1 ,i will not make an old dotard   
out of ,saturn1 and two servants for him
 out of his companion orbs1 but rather  
out of those three united bodies ,i will
 make a triple ,geryon1 out of ,galileo 
,hercules1 and out of the telescope his 
club1 armed with which1 ,galileo has    
conquered that most distant of the      
planets1 drawn it out of the furthest   
recesses of nature1 dragged it down to  
earth1 and exposed it to the gaze of us 
all4 ,it pleases me too1 now that the   
nest has been found1 to consider with   
curiosity what kind of brood must be in 
it1 what kind of life1 if there be any  
life there1 between orbs which all but  
touch each other two and two1 where not 
even                                  8a
 space     ,of sky extends not more than
 three ells wide10#bd  but where there  
is scarcely a chink of a nail's-breadth 
all round4      #bd ,virgil1 ,eclog4    
iii4 #aje4  ,do indeed the astrologers  
rightly ascribe to ,saturn the          
guardianship of miners1 who1 accustomed 

to spend their lives1 like moles1       
underground1 seldom breathe the free air
 under the open sky8 ,although the      
darkness here is rather more supportable
 than in ,saturn1 because the sun1 which
 appears there only as large as ,venus  
appears to us on the earth1 continually 
casts its rays through the spaces       
between the different orbs in such a way
 that those inhabitants who are situated
 on one orb are covered by the other as 
by a ceiling2 while those on the latter 
orb1 on the top of this roof of theirs1 
exposed as it is to the full light of   
the sun1 receive a glare as if from very
 firebrands4 ,but ,i must draw in the   
reins and check my mind in its enjoyment
 of the free fields of ether2 for fear1 
perchance1 later observations should    
report something different from the     
first account1 something changed in     
course of time4#be      #be ,the        
completion of ,galileo's observations on
 ,saturn depended     on the improvement
 of astronomical instruments1 as will be

 evident     from the following sketch4 
,galileo made out the first indications 
of ,saturn's ring in #afaj1 as narrated 
in his letter1 with a power     of      
thirty2 but in ,december #afab he wrote 
to one of his friends1     ,marco       
,velseri1 that he could no longer see   
these indications1     and began to     
imagine that his telescope had deceived 
him1 and     apparently abandoned       
further researches4 ,hevelius in #afdb  
saw     the ring more clearly1 but      
figured it as two crescents attached    
to ,saturn by their cusps4 ,at length1  
in #afec1 ,huyghens provided     himself
 with a power of one hundred1 having    
made the lenses with     his own hands1 
and immediately discovered the          
explanation of the     phenomena which  
had baffled previous observers4 ,he     
published his     explanation of        
,saturn's ring1 and his discovery of the
 first     satellite1 in his ,systema   
,saturnium1 #afei4 ,cassini1 with still 
more powerful instruments1 discovered   

four more satellites in     #afga1      
#afgb1 #afhd4 ,sir ,william ,herschel in
 #aghi detected two     more1 8which can
 only be seen with telescopes of        
extraordinary     power and perfection1 
and under the most favourable           
atmospheric                             
circumstances40--7,,herschel1 ,outlines 
of ,astronomy1  #edh47 ,and the     last
 of the eight satellites was discovered 
in #ahdh by ,lassell of     ,liverpool1 
and ,bond of ,cambridge1 ,u4,s41        
simultaneously4  ,at the end of his     
letter ,galileo seemed to think that he 
had come to the end of his reports about
 the planets1 and observations of new   
phenomena respecting them1 but ever on  
the watch1 that eye of his1 that one not
 of ,nature's making--,i mean his       
telescope--in a short time made more    
discoveries1 concerning which read the  
following letter of ,galileo3--         
,sidenote3 ,account of ,galileo's       
discovery of the phases of ,venus4      
8,di ,firenze li #aa di ,decembre       

#afaj4--,sto con desiderio1 attendendo  
la risposta a due mie scritte           
ultimamente per sentire quello1 che     
aver detto il ,sig4 ,keplero della      
stravaganza di ,saturno4 ,intanto       
mando a ,vostra ,signoria ,illustrissima
 e ,reverendissima la cifra     di un   
altro particolare osservato da me       
nuovamente1 il quale si     tira dietro 
la decisione di grandissime controversie
 in ,astronomia1     ed in particolare  
contiene in se un gagliardo argomento   
per la     constitutione ,pitagorica e  
,copernicana dell',universo2 e a suo    
tempo pubblicher la deciferazione ed    
altri particolari4 ,spero che     aver  
trovato il metodo per definire i periodi
 dei quattro ,pianeti     ,medicei1     
stimati con gran ragione quasi          
inesplicabili dal ,sig4     ,keplero1 al
 quale piacer1 ec4      8,le lettere    
trasposte sono queste3      8,haec      
immatura a me jam frustra leguntur1     
o4y40  ,which may be translated thus3-- 
8,i am anxiously looking for an answer  

to my last two letters1 that     ,i may 
learn what ,kepler says about the       
marvels of ,saturn's orb4     ,in the   
meantime ,i send him a riddle concerning
 a certain new and     splendid         
observation which tends to decide great 
controversies in     astronomy2 and     
especially contains a fine argument in  
favour of the     ,pythagorean and      
,copernican system of the universe4 ,at 
the proper     time ,i will publish the 
solution of the riddle1 and some other  
particulars4 ,i hope that ,i have found 
a method of determining the     periodic
 times of the four ,medicean planets1   
which ,kepler1 not     without very good
 reason1 thought inexplicable1 etc4     
8,the letters turned into an anagram1   
are these3      8,haec immatura a me jam
 frustra leguntur1 o4y40  ,so far       
,galileo4 ,but if1 reader1 this letter  
has filled you with a desire to know the
 meaning contained in those letters1    
then you must read another letter of    
,galileo which follows4  ,illustration3 

,fig4 #a4  ,e the ,earth 7centre of     
universe74 ,s the ,sun4 ,c centre of    
eccentric4 ,d centre of planet's        
epicycle4 ,,vv' stationary points4 s v  
v' projections of ,,svv' on the ecliptic
 of which ,e is the centre4             
,illustration3 ,fig4 #b4  ,s the ,sun1  
centre of solar system4 v e positions of
 planet and ,earth at conjunction4 ,,vv'
 stationary points of planet4 ,,ee'     
corresponding positions of the ,earth4  
,but before you do so1 ,i should like   
you to notice1 by the way1 what ,galileo
 says about the ,pythagorean and        
,copernican system of the universe4 ,for
 he points to my ,mystery of the        
,universe1#bf published fourteen years  
ago1 in which ,i took the dimensions of 
the ,planetary orbits according to the  
astronomy of ,copernicus1 who makes the 
sun immovable in the centre1 and the    
earth movable both round the sun and    
upon its own axis2 and ,i showed that   
the differences of their orbits         
corresponded to the five regular        

,pythagorean figures1 which had been    
already distributed by their author     
among the elements of the world1 though 
the attempt was admirable rather than   
happy or legitimate1 and for which      
figures' sake ,euclid wrote the whole of
 his ,geometry4 ,now1 in that ,mystery  
you may find a sort of combination of   
,astronomy and ,euclid's ,geometry1 and 
through this combination a most thorough
 completion and finishing of them both2 
and this was the reason why ,i waited   
with intense longing to see what sort of
 an argument ,galileo would produce in  
favour of the ,pythagorean system of the
 universe4 ,after this explanation1     
,galileo's letter about this argument   
was as follows3--      #bf ,kepler1 in  
his ,mystery of the ,universe1          
endeavoured to     connect the orbits of
 the planets with the five regular      
solids1     thus3 ,if in a sphere 7i47 a
 cube be inscribed1 and in the cube     
a sphere 7ii472 and in that sphere a    
tetrahedron1 and in the     tetrahedron 

a sphere 7iii472 and in that sphere a   
dodecahedron1     and in the            
dodecahedron a sphere 7iv472 and in that
 sphere an     icosahedron1 and in the  
icosahedron a sphere 7v472 and in that  
sphere an octahedron1 and in the        
octahedron a sphere 7vi471     the      
diameters of these six spheres will be  
proportional to the     diameters of the
 orbits of ,saturn1 ,jupiter1 ,mars1 the
 ,earth1 ,venus1     and ,mercury       
respectively2 or1 as ,kepler expresses  
it1 the common     centre of these      
spheres represents the position of the  
,sun1 and the     six spheres represent 
the spheres of the planets4      ,by    
these considerations1 however1 ,kepler  
was led to enunciate     his third law1 
that the squares of the periodic times  
of planets     are proportional to the  
cubes of their mean distances from the  
sun4--,,kepler1 ,prodromus              
,dissertationum ,mathematicarum         
continens     ,mysterium                
,cosmographicum1 etc4 7,tbingen1 #aeif47

      8,illustrissimo e ,reverendissimo 
,signore mio colendissimo4      8 tempo 
che io deciferi a ,vostra ,signoria     
,illustrissima e     ,reverendissima e  
per lei al ,sig4 ,keplero le lettere    
trasposte     le quali alcune settimane 
sono le inviai2  tempo dico1 giacch     
sono interamente chiaro della verit del 
fatto1 sicch non ci     resta un minimo 
scrupolo1 o dubbio4 ,sapranno dunque    
come circa a     tre mesi fa vedendosi  
,venere vespertina la cominciai ad      
osservar     diligentemente             
coll'occhiale1 per veder col senso      
stesso     quello di che non dubitava   
punto l'intelletto4 ,la vidi dunque sul 
principio di figura rotonda1 pulita e   
terminata1 ma molto picciola2     di tal
 figura si mantenne sino che cominci ad 
avvicinarsi alla     sua massima        
digressione1 ma tra tanto and crescendo 
in mole4     ,cominci poi a mancare     
dalla rotondit nella sua parte orientale
     ed avversa al ,sole1 e in pochi    
giorni si ridusse ad esser un mezzo     

cerchio perfettissimo1 e tale si        
mantenne1 senza punto alterarsi1        
finch incominci  ritirarsi verso il     
,sole1 allontanandosi     dalla         
tangente4 ,ora va calando dal mezzo     
cerchio1 e si mostra     cornicolata1 e 
ander assottigliandosi sino             
all'occultazione1     riducendosi allora
 con corna sottilissime4 ,quindi        
passando all'     apparizione mattutina1
 la vedremo pur falcata1 e sottilissima 
e     colle corna avverse al ,sole2     
ander poi crescendo fino alla massima   
digressione1 dove apparir semicircolare1
 e tale senza alterarsi si     manterr  
molti giorni1 e poi dal mezzo cerchio   
passer presto al     tutto tondo1 e cos 
rotonda si conserver poi per molti mesi4
 ,il     suo diametro adesso  circa     
cinque volte maggiore di quello1 che    
si mostrava nella sua prima apparizione 
vespertina2 dalla quale     mirabile    
esperienza abbiamo sensata1 e certa     
dimostrazione di due     gran questioni 
state fin qui dubbie tr i maggiori      

ingegni del     ,mondo4 ,l'una 1 che i  
,pianeti tutti son di lor natura        
tenebrosi     7accadendo anco a         
,mercurio l'istesso1 che a ,venere74    
,l'altra1 che     ,venere               
necessarissimamente si volge intorno al 
,sole1 come anco     ,mercurio1 cosa1   
che degli altri ,pianeti1 fu creduta da'
 ,pitagorici1     dal ,copernico1 dal   
,keplero e da' loro seguaci1 ma non     
sensatamente     provata1 come ora in   
,venere1 ed in ,mercurio4               
8,averanno dunque il ,sig4 ,keplero1 e  
gli altri ,copernicani da     gloriarsi 
di aver creduto e filosofato bene1      
sebbene ci  toccato1     e ci  per      
toccare ancora ad esser reputati dall'  
universit dei     ,filosofi in libris1  
per poco intendenti1 e poco meno che    
stolti4      8,le parole dunque1 che    
mandai trasposte1 e che dicevano1       
,haec immatura a me jam frustra         
leguntur1 o4y4      dicono ordinate     
,cynthiae figuras aemulatur mater       
amorum4      8,cio1 che ,venere imita le

 figure della ,luna4 ,osservai tre notti
     sono l'ecclisse1 nella quale non vi
  cosa notabile1 solo si vede     il    
taglio dell'ombra indistinto1 confuso e 
come annebbiato1     e questo per       
derivare essa ombra dalla ,terra        
lontanissima da     essa ,luna4 ,voleva 
scrivere altri particolari1 ma essendo  
stato     trattenuto molto da alcuni    
gentiluomini1 ed essendo l'ora          
tardissima1 son forzato a finire4       
,favoriscami salutare in mio nome     i 
,,ss4 ,keplero1 ,asdale e ,segheti1 ed a
 ,vostra ,signoria ,illustrissima       
con ogni reverenza bacio le mani1 e dal 
,signore ,dio gli prego     felicit4 ,di
 ,firenze il primo di ,gennaio #afaj4   
,ab ,incarnatione4      8,di ,vostra    
,signoria ,illustrissima e              
,reverendissima ,servidore              
obbligatissimo4      ,galileo ,galilei40
  ,such is ,galileo's letter2 but let me
 give you the substance of it3--        
8,it is time for me to disclose the     
method of reading the letters     which 

some weeks since ,i sent you as an      
anagram4 ,it is time now1 ,i     mean1  
after ,i have become quite certain about
 the matter1 so much     so that ,i have
 no longer even a shadow of doubt4 ,you 
must know then     that about three     
months ago1 when the star of ,venus     
could be seen1     ,i began to look at  
it through a telescope with great       
attention1     so that ,i might grasp   
with my physical senses an idea which ,i
 was     entertaining as certain4 ,at   
first then you must know the planet     
,venus appeared of a perfectly circular 
form1 accurately so1 and     bounded by 
a distinct edge1 but very small2 this   
figure ,venus kept     until it began to
 approach its greatest distance from the
 sun1     and meanwhile the apparent    
size of its orb kept on increasing4     
,from that time it began to lose its    
roundness on the eastern side1     which
 was turned away from the sun1 and in a 
few days it contracted     its visible  
portion into an exact semicircle2 that  

figure lasted     without the smallest  
alteration until it began to return     
towards     the sun where it leaves the 
tangent drawn to its epicycle4#bg       
,at this time it loses the semicircular 
form more and more1 and     keeps on    
diminishing that figure until its       
conjunction1 when it     will wane to a 
very thin crescent4 ,after completing   
its passage     past the sun1 it will   
appear to us1 at its appearance as a    
morning     star1 as only sickle-shaped1
 turning a very thin crescent away from 
the sun2 afterwards the crescent will   
fill up more and more until     the     
planet reaches its greatest distance    
from the sun1 in which     position it  
will appear semicircular1 and that      
figure will last     for many days      
without appreciable variation4 ,then by 
degrees1 from     being semicircular it 
will change to a full orb1 and will keep
 that     perfectly circular figure for 
several months2 but at this instant     
the diameter of the orb of ,venus is    

about five times as large as     that   
which it showed at its first appearance 
as an evening star4       8,from the    
observation of these wonderful phenomena
 we are supplied     with a             
determination most conclusive1 and      
appealing to the evidence     of our    
senses1 of two very important problems1 
which up to this     day were discussed 
by the greatest intellects with         
different     conclusions4 ,one is that 
the planets are bodies not self-luminous
     7if we may entertain the same views
 about ,mercury as we do about          
,venus74 ,the second is that we are     
absolutely compelled to say     that    
,venus 7and ,mercury also7 revolves     
round the sun1 as do also     all the   
rest of the planets4 ,a truth believed  
indeed by the     ,pythagorean school1  
by ,copernicus1 and by ,kepler1 but     
never proved     by the evidence of our 
senses1 as it is now proved in the case 
of     ,venus and ,mercury4 ,kepler     
therefore and the rest of the school    

of ,copernicus have good reason for     
boasting that they have shown           
themselves good philosophers1 and that  
their belief was not devoid     of      
foundation2 however much it has been    
their lot1 and may even     hereafter be
 their lot1 to be regarded by the       
philosophers of our     times1 who      
philosophise on paper1 with an universal
 agreement1 as     men of no intellect1 
and little better than absolute fools4  
8,the words which ,i sent with their    
letters transposed1 and which     said1 
,haec immatura a me jam frustra         
leguntur1 o4y4      when reduced to     
their proper order1 read thus1          
,cynthiae figuras aemulatur mater       
amorum3       ,the mother of the ,loves 
rivals the phases of ,cynthia3      that
 is1        ,venus imitates the phases  
of the ,moon4      8,three days ago ,i  
observed an eclipse of the moon1 but not
 anything     worthy of special notice  
occurred in it4 ,only the edge of the   
shadow appeared indistinct1 blurred1 and

 hazy2 the cause of the     phenomenon  
no doubt is that the shadow has its     
origin at the earth1     at a great     
distance from the body of the moon4     
8,i have some other particulars1 but ,i 
am prevented by time from     writing   
about them1 etc40  ,so writes ,galileo4 
#bg ,in the ,ptolemaic system the       
earth's centre was regarded as the      
centre of the universe1 and the         
movements of the heavenly bodies        
were explained by eccentrics and        
epicycles4 ,the sun was conceived     to
 describe a circle about a point not    
exactly coinciding with the     centre  
of the earth1 called the sun's          
eccentric4 ,the planets     described   
epicycles 7circles7 whose centres       
described eccentrics     7circles71 and 
the centres of these eccentrics         
coincided with the     centre of the    
sun's eccentric4 ,in the case of        
,mercury and ,venus     the centre of   
the epicycle was always on the line     
drawn from the     centre of the        

eccentric to the sun's centre4 ,in the  
case of the     other planets the       
construction was more complicated4 ,the 
stationary     points were determined by
 drawing tangents from the earth's      
centre     7or the observer7 to the     
epicycle1 as in the figure              
7#a74--7;,,gassendi1     ,institutio    
,astronomica1 #afdg47 ,this will explain
 ,kepler's     description of the       
stationary points as the points where   
the     planet leaves the tangent to its
 epicycle1 supposing that he uses       
the terms of the current 7i4e4          
,ptolemaic7 astronomy4 ,copernicus      
placed the sun instead of the earth at  
the centre of the universe1     but to  
determine the positions of the planets  
at any given time     with as much      
accuracy as was attainable with the     
,ptolemaic system1     he was obliged to
 use a similar method of eccentrics and 
epicycles1     so that ,kepler's        
expression may be understood to describe
 the     stationary points according to 

the ,copernican theory1 though it     is
 still strange that he should not       
recognise the elliptical form     of the
 planetary orbits1 which he had lately  
demonstrated after     most laborious   
reasoning in his ,commentaries on the   
,motion of the     ,planet ,mars1 #afji4
 ,galileo's own expression seems to     
describe the     stationary points      
according to the ,copernican system1 as 
would be     expected1 as the points    
where the planet leaves the tangent     
drawn     to its orbit from the earth   
7,fig4 #b74  ,what now1 dear reader1    
shall we make out of our telescope8     
,shall we make a ,mercury's magic-wand  
to cross the liquid ether with1 and1    
like ,lucian1#bh lead a colony to the   
uninhabited evening star1 allured by the
 sweetness of the place8 or shall we    
make it a ,cupid's arrow1 which1        
entering by our eyes1 has pierced our   
inmost mind1 and fired us with a love of
 ,venus8 ,for what language is too      
strong for the marvellous beauty of this

 orb1 if1 having no light of its own1 it
 can attain simply by the borrowed light
 of the sun to such splendour1 as       
,jupiter has not1 nor the moon1 though  
enjoying a proximity to the sun as close
 as ,venus2 for if the moon's light be  
compared with the light of ,venus1 it   
will be seen to be certainly greater on 
account of the apparent magnitude of the
 moon1 but1 in comparison with the light
 of ,venus1 dull1 dead1 and leaden4 ,o  
truly golden ,venus6 ,will any one doubt
 any more that the whole orb of ,venus  
is wrought most smoothly out of pure    
unalloyed gold1 since its surface1 when 
only placed in the sunlight1 reflects a 
splendour so intense6 ,and here let me  
add my experiments about the alteration 
of the light of ,venus on blinking the  
eye1 which ,i have examined in the part 
of my ,astronomy which treats of        
,optics4 ,reasoning will be able to     
conclude nothing else but this1 that the
 orb of ,venus turns on its own axis    
with an exceedingly swift rotation1     

displaying one after another different  
parts of its surface which are more or  
less capable of retaining the sun's     
light4#bi      #bh ,lucian1 ,ver4 ,hist4
 i4 #ab4      #bi ,the first scientific 
determination of the period of the      
rotation of ,venus was made by          
,dominique ,cassini in #afff1 from      
observations of spots on the planet1 and
 concluded to be about #bd     hours2   
but in #agbf ,bianchini deduced a period
 of #bd d4 #h h4 from     similar       
observations4 ,the true period is       
considered to be #bc h4 #ba     m41     
determined by ,schroeter by a series of 
observations lasting     from #aghh to  
#agic on the periodicity of the         
deformation of the     horns of         
,venus4--7,,arago1 ,astronomie          
,populaire1 #ahed47      ,kepler's      
statements can only be regarded as      
anticipations of     phenomena not yet  
actually observed4  ,but enough of my   
own conclusions4 ,let us now hear as an 
epilogue ,galileo's conclusions built up

 out of all the observations which he   
has made with his telescope1 and        
announced from time to time4 ,thus he   
writes once more3--  ,sidenote3         
,galileo's conclusions with regard to   
the inherent nature of the brightness of
 the stars4      8,illustrissimo e      
,reverendissimo ,signore mio            
colendissimo4      8,ho ricevuto gusto1 
e contento particolarissimo nella       
lettura     dell' ultima di ,vostra     
,signoria ,illustrissima e              
,reverendissima     delli #g stante1 ed 
in particolare in quella parte dove ella
     m'accenna la favorevole            
inclinazione dell' ,illustriss4 ,sig4   
,cons4 ,wackher1 verso di me1 la quale  
io infinitamente stimo1     ed apprezzo2
 e poich quella ha principalmente       
origine dall'     aver io incontrate    
osservazioni necessariamente dimostranti
     conclusioni per avanti tenute vere 
da sua ,signoria ,illustrissima     per 
confermarmi maggiormente il possesso di 
grazia tanto pregiata     da me1 prego  

,vostra ,signoria ,illustrissima e      
,reverendissima a     fargli intendere  
per mia parte come conforme alla        
credenza di     ,sua ,signoria          
,illustrissima ho dimostrazione certa1  
che siccome     tutti i ,pianeti        
ricevono il lume dal ,sole1 essendo per 
se stessi     tenebrosi1 e opachi2 cos  
le ,stelle fisse risplendono per lor    
natura1 non bisognose dell'             
illustrazione de' raggi solari1 li      
quali1 ,dio sa1 se arrivino a tanta     
altezza1 pi di quello1 che     arrivi a 
noi il lume di una di esse fisse4 ,il   
principal fondamento     del mio        
discorso  nell' osservare io molto      
evidentemente con     gli occhiali che  
quei ,pianeti di mano in mano1 che si   
trovano     pi vicini a noi1 o al ,sole1
 ricevono maggiore splendore1 e pi      
illustremente ce lo riverberano2 e perci
 ,marte perigeo1 e a noi     vicinissimo
 si vede assai pi splendido1 che ,giove2
 bench a     quello di mole assai       
inferiore2 e difficilmente se gli pu    

coll'     occhiale levare quella        
irradiazione1 che impedisce il vedere il
 suo     disco terminato1 e rotondo2 il 
che in ,giove non accade1 vedendosi     
esquisitamente circolare4 ,saturno poi  
per la sua gran lontananza     si vede  
esattamente terminato1 s la ,stella     
maggiore di mezzo1     come le due      
piccole laterali2 ed appare il suo lume 
languido1 ed     abbacinato e senza     
niuna irradiazione1 che impedisca il    
distinguere     i suoi tre piccoli globi
 terminatissimi4 ,ora poich apertamente 
veggiamo1 che il ,sole molto            
splendidamente illustra ,marte vicino1  
e che molto pi languido  il lume di     
,giove 7sebbene senza lo     strumento  
appare assai chiaro1 il che accade per  
la grandezza1 e     candore della       
,stella7 languidissimo1 e fosco quello  
di ,saturno1     come molto pi lontano1 
quali doveriano apparirci le ,stelle    
fisse lontane indicibilmente pi di      
,saturno1 quando il lume loro           
derivasse dal ,sole8 ,certamente        

debolissime1 torbide e smorte4 ,ma      
tutto l'opposito si vede1 perocch se    
rimireremo per esempio il     ,cane1    
incontreremo un fulgore vivissimo1 che  
quasi ci toglie la     vista1 con una   
vibrazione di raggi tanto fiera1 e      
possente1 che     in comparazione di    
quello rimangono i ,pianeti1 e dico     
,giove e     ,venere stessa1 come un    
impurissimo vetro appresso un           
limpidissimo     e finissimo diamante4  
,e bench il disco di esso ,cane         
apparisca non     maggiore della        
cinquantesima parte di quello di ,giove1
 tuttavia la     sua irradiazione       
grande1 e fiera in modo1 che l'istesso  
globo     tra i proprii crini s'implica1
 e quasi si perde1 e con qualche        
difficolt si distingue2 dove che ,giove 
7e molto pi ,saturno7     si vedono e   
terminati1 e di una luce languida1 e per
 cos dire     quieta4 ,e per tanto io   
stimo1 che bene filosoferemo1 referendo 
la     causa della scintillazione delle 
,stelle fisse1 al vibrare1 che elle     

fanno dello splendore proprio e nativo  
dall'intima loro sustanza2     dove che 
nella superficie de' ,pianeti termina pi
 presto1 e si     finisce               
l'illuminazione1 che dal ,sole deriva1 e
 si parte4 ,se io     sentir qualche    
particolare questione ricevuta dal      
medesimo ,sig4     ,wackher1 non rester 
d'affaticarmivi intorno1 per            
dimostrarmi1     quale io sono          
desiderosissimo di servire un tanto     
,signore1 e non     gi con isperanza di 
aggiungere al termine conseguito dal suo
     discorso1 perch benissimo          
comprendo1 che a quanto sia passato     
per lo finissimo cribro del giudizio di 
esso1 e del ,sig4 ,keplero1     non si  
pu aggiungere di squisitezza2 n io      
pretenderei altro1     che col dubitare1
 e mal filosofare1 eccitar loro al      
ritrovamento     di nuove sottigliezze4 
,gl'ingegni singolari1 che in gran      
numero     fioriscono nell',alemagna1 mi
 hanno lungo tempo tenuto in desiderio  
di vederla1 il qual desiderio ora si    

raddoppia per la nuova grazia           
dell',illustrissimo ,sig4 ,wackher1 la  
quale mi farebbe divenir     grande ogni
 picciola occasione1 che mi si          
presentasse4 ,ma ho di     soverchio    
occupata ,vostra ,signoria              
,illustrissima e ,reverendissima4       
,degnisi per fine di offerirmi e        
dedicarmi devotissimo servidore         
all',illustrissimo ,sig4 ,wackher1      
salutando anco caramente il ,sig4       
,keplero1 ed a lei con ogni riverenza   
bacio le mani1 e dal ,signore     ,dio  
le prego somma felicit4      8,di       
,firenze li #bf di ,marzo #afaa4 ,di    
,vostra ,signoria ,illustrissima     e  
,reverendissima obbligatissimo          
,servidore1      ,,galileo ,,galilei40  
,when translated1 the meaning is as     
follows3--      8,your last letter has  
exceedingly pleased me1 especially that 
part     which assures me of the        
friendly feeling entertained towards me 
by     the most illustrious ,imperial   
,counsellor1 ,wagher1 which ,i for my   

part highly appreciate4 ,and since the  
cause of this friendliness     is1 that 
,i have incontestably demonstrated by   
some observations of     mine certain   
conclusions which he had long held as   
true1 ,i wish     to confirm my         
possession of favour1 which ,i value so 
much1 and     accordingly ,i ask you to 
give him this piece of news from me2    
that     ,i have most conclusive        
arguments ready1 showing clearly that1  
just     as he holds1 all the planets   
receive their light from the sun1       
being by constitution bodies dark and   
devoid of light2#cj but that     the    
fixed stars shine by their own proper   
light1 not needing to be     illuminated
 by the sun's rays1 since ,god knows    
whether they reach     the very remote  
region of the fixed stars with intensity
 even equal     to the small intensity  
with which the rays of the fixed stars  
come     down to us4      8,my          
demonstration depends chiefly on this   
fact1 that with the     telescope ,i    

have distinctly observed that the       
planets receive     greater brightness1 
and reflect it more intensely1 in       
proportion     as each one is nearer to 
us and to the sun4 ,so ,mars in perigee1
     that is1 when nearest to the earth1
 greatly surpasses ,jupiter in          
brightness1 although in actual size it  
is far inferior to ,jupiter2     and in 
consequence it is difficult to receive  
the effulgence of     this planet in the
 telescope1 for it is so great as to    
prevent the     eye from being able to  
distinguish the circular termination of 
the     planet's disc4 ,this does not   
happen in the case of ,jupiter1 for it  
appears quite circular4 ,the next       
planet1 ,saturn1 on account of its      
great distance likewise--for indeed it  
is the most remote of the               
planets1--appears bounded by a          
well-defined edge1 both the greater     
orb in the middle and the two small orbs
 at its sides4 ,indeed1     it appears  
to shine with a faint and delicate      

light1 without any     effulgence to    
prevent an observer recognising the     
well-defined     termination of its     
three orbs4 ,since1 then1 we see that   
,mars1 the     nearest of the three1 is 
illumined by the sun with very great    
splendour1 and that the light of        
,jupiter1 at a greater distance1     is 
much more faint 7although without the   
use of an instrument it     appears     
tolerably bright1 which is due to the   
size and brilliancy     of its body71   
and that the light of ,saturn1 at the   
greatest     distance1 is most faint1   
and almost watery1 of what kind1 do you 
think1 would appear the light of the    
fixed stars1 which are at an            
immeasurable distance further from the  
sun than ,saturn1 if they     only      
received light from the sun8 ,most      
certainly1 extremely feeble1            
indistinct1 and pallid4 ,and yet we find
 quite the contrary2 for1     let us    
look with our eyes at the ,dog-,star1   
for example4 ,we shall     encounter a  

most vivid brilliancy1 which almost     
pricks the eye     with the rapid       
sparkling of its rays1 of such intensity
 that1 in     comparison with it1 the   
planets1 even ,jupiter1 and ,venus too1 
are     as thoroughly outshone as common
 and bad glass compared with a          
highly polished and most sparkling      
diamond4 ,and although the orb of       
the ,dog-,star appears no larger than   
the fiftieth part of ,jupiter's         
disc1 nevertheless its brilliancy is    
great and very strong2 so that     the  
form of its disc1 which you expect to   
see1 hides itself among     the rays of 
its own refulgence1 envelops itself in  
them1 and almost     disappears2 and it 
is not distinguished without some       
difficulty     from the rays which      
surround it4 ,whereas ,jupiter1 and     
still     more ,saturn1 are seen well   
defined2 and their light is without     
intensity1 and1 if ,i may say so1       
quiescent4 ,wherefore ,i think that     
we shall rightly apply our philosophy if

 we refer the cause of the     twinkling
 of the fixed stars to vibrations of a  
brilliancy1 which     is their own1     
belonging to their constitution1 and    
inherent in     their substance1 and    
say1 on the other hand1 that the        
illumination     of the planets1 which  
is derived from the sun1 and distributed
 to     the world1 is limited to their  
surface40  ,these are the scientific    
conclusions in ,galileo's letter2 the   
rest ,i omit4      #cj ,proctor 7,other 
,worlds than ,ours1 #ahge7 has given    
some     reasons for believing that     
,jupiter and ,saturn shine in part with 
their own light1 owing to their great   
internal heat4  ,you see then1 studious 
reader1 how the subtle mind of ,galileo1
 in my opinion the first philosopher of 
the day1 uses this telescope of ours    
like a sort of ladder1 scales the       
furthest and loftiest walls of the      
visible world1 surveys all things with  
his own eyes1 and1 from the position he 
has gained1 darts the glances of his    

most acute intellect upon these petty   
abodes of ours--the planetary spheres ,i
 mean1--and compares with keenest       
reasoning the distant with the near1 the
 lofty with the deep4       ,,vale ,,et 
,,deum ,,in ,,operibus ,,suis           
,,celebrare ,,nunquam ,,desine4         
,,kepler1 ,narratio4   ,edinburgh       
,university ,press3  ,,thomas ,,and     
,,archibald ,,constable1 ,,printers ,,to
 ,,her ,,majesty4