Only, Alcina fairest was by far
  As is the sun more fair than every star.... 
  Milk is the bosom, of luxuriant size,
  And the fair neck is round and snowy white;
  Two unripe ivory apples fall and rise
  Like waves upon the sea-beach when a slight
  Breeze stirs the ocean. (Canto 7.)

  Now in a gulf of bliss up to the eyes
  And of fair things, to swim he doth begin. 
          (Canto 7.)

  So closely doth the ivy not enlace
  The tree where firmly rooted it doth stand,
  As clasp each other in their warm embrace
  These lovers, by each other’s sweet breath fanned. 
  Sweet flower, of which on India’s shore no trace
  Is, or on the Sabaean odorous sand. 
          (Canto 7.)

  Her fair face the appearance did maintain
  That sometimes shewn is by the sky in spring,
  When at the very time that falls the rain,
  The sun aside his cloudy veil doth fling. 
  And as the nightingale its pleasant strain
  Then on the boughs of the green trees doth sing,
  Thus Love doth bathe his pinions at those bright
  But tearful eyes, enjoying the clear light. 
          (Canto 11.)

But as more fickle than the leaf was she,
When it in autumn doth more sapless grow,
And the old wind doth strip it from the tree,
And doth before it in its fury grow. 

          
                                                                    (Canto 21.)

He uses the sea: 

As when a bark doth the deep ocean plough,
That two winds strike with an alternate blast,
’Tis now sent forward by the one, and now
Back by the other in its first place cast,
And whirled from prow to poop, from poop to prow,
But urged by the most potent wind at last
Philander thus irresolute between
The two thoughts, did to the least wicked lean. 

          
                                                                      (Canto 21.)

As comes the wave upon the salt sea shore
Which the smooth wind at first in thought hath fanned;
Greater the second is than that before
It, and the third more fiercely follows, and
Each time the humour more abounds, and more
Doth it extend its scourge upon the land: 
Against Orlando thus from vales below
And hills above, doth the vile rabble grow. 

          
                                                                          (Canto 24.)

These comparisons not only shew faithful and personal observation, but are far more subjective and subtle than, for instance, Dante’s.  The same holds good of Tasso.  How beautiful in detail, and how sentimental too, is this from Jerusalem Delivered: 

Behold how lovely blooms the vernal rose
When scarce the leaves her early bud disclose,
When, half unwrapt, and half to view revealed,
She gives new pleasure from her charms concealed. 
But when she shews her bosom wide displayed,
How soon her sweets exhale, her beauties fade! 
No more she seems the flower so lately loved,
By virgins cherished and by youths approved. 
So swiftly fleeting with the transient day
Passes the flower of mortal life away.