There is certainly in our natural Capacities themselves, a Fitness for some Things, and Unfitness for others.  Thus whatever great Capacities a Man may have, if he is naturally timorous, or a Coward, he never can have a Warlike Genius.  If a Man has not a good Judgment, how great soever his Wit may be, or polite his Manners, he never will have the Genius of a Statesman.  Just as strong Sounds and brisk Measures can never touch the softer Passions.  Yet as the Art and Skill of the Composer, is required to the Genius of Musick, so is a Knowledge of the Force and Power of the natural Capacity, and a judicious Application of it to the best and most proper Purposes, what forms a Genius for any Thing.  This is the effect of Care, Experience and a right Improvement of every Advantage that offers.  On this Observation Horace founded his Rules for a Poetical Genius.

Versate diu quid sere recusent
Quid valeant humeri.
And,
Ego nec studium sine divite vena,
Nec rude quid profit video ingenium.

To speak my Thoughts, I hardly know
What witless Art, or artless Wit can do.

The same Observation in another kind is elegantly described by Mr. Waller.

Great Julius on the Mountains bred,
A Flock perhaps, or Herd had led. 
He that the World subdued, had been
But the best Wrestler on the Green. 
’Tis Art and Knowledge that draw forth
The hidden Seeds of Native Worth. 
They blow those Sparks, and make ’em rise
Into such Flames as touch the Skies.

The High and Martial Spirit of Casar would have inclined and fitted him, to gain the Prize of Wrestling above any Country Sport.  But it was the Circumstance of his own Birth and Fortune, the State and Condition of the Commonwealth, and the Concurrence of many other Advantages, which he improv’d with great Care and Application, that made him a finish’d Genius, both in Arms and Policy.

There is yet another Thing of Consequence to a true Genius in Musick.  A Knowledge of the Compass and peculiar Advantages of each several Instrument.  For the same Composition will very differently touch both the Ear and the Mind, as perform’d by a Flute, or Trumpet, an Organ, or a Violin.  A difference of which, all discern by the Ear, but which requires a judicious Observation in the Composer.  Mr. Hughes has thus express’d their different Powers.

Let the Trumpet’s shrill Voice,
And the Drum’s thundering Noise
Rouse every dull Mortal from Sorrow profound.
And_,
Proceed, sweet Charmer of the Ear,
Proceed, and through the mellow Flute,
The moving Lyre,
And Solitary Lute,
Melting Airs, soft Joys inspire,
Airs for drooping Hope to hear.
And again,
Now, let the sprightly Violin
A louder Strain begin: 
And now,
Let the deep mouth’d Organ blow,