M 119121] Observations of the Moon 151 



tains, the largest being estimated by him to be about four 

 miles high, a result agreeing closely with modern estimates 

 of the greatest height on the moon. The large dark spots 

 he explained (erroneously) as possibly caused by water, 

 though he evidently had less confidence in the correctness 

 of the explanation than some of his immediate scientific 

 successors, by whom the name of seas was given to 

 these spots (chapter viu., 153). He noticed also the 

 absence of clouds. Apart however from details, the really 

 significant results of his observations were that the moon 

 was in many important respects similar to the earth, that 

 the traditional belief in its perfectly spherical form had 

 to be abandoned, and that so far the received doctrine of 

 the sharp distinction to be drawn between things celestial 

 and things terrestrial was shewn to be without justification ; 

 the importance of this in connection with the Coppernican 

 view that the earth, instead of being unique, was one of 

 six planets revolving round the sun, needs no comment. 



One of Galilei's numerous scientific opponents * attempted 

 to explain away the apparent contradiction between the old 

 theory and the new observations by the ingenious sugges- 

 tion that the apparent valleys in the moon were in reality 

 filled with some invisible crystalline material, so that the 

 moon was in fact perfectly spherical. To this Galilei 

 replied that the idea was so excellent that he wished to 

 extend its application, and accordingly maintained that 

 the moon had on it mountains of this same invisible sub- 

 stance, at least ten times as high as any which he had 

 observed. 



1 20. The telescope revealed also the existence of an 

 immense number of stars too faint to be seen by the 

 unaided eye ; Galilei saw, for example, 36 stars in the 

 Pleiades, which to an ordinary eye consist of six only. 

 Portions of the Milky Way and various nebulous patches 

 of light were also discovered to consist of multitudes of 

 faint stars clustered together; in the cluster Praesepe (in 

 the Crab), for example, he counted 40 stars. 



121. By far the most striking discovery announced in the 

 Sidereal Messenger was that of the bodies now known as 



* Ludovico delle Colombe in a tract Contra II Moto della Terra, 

 which is reprinted in the national edition of Galilei's works, Vol. III. 



